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Generally, the IV characteristics of Langmuir probes are defined for unmagnetized plasma. How to estimate the electron temperature and plasma density let's say if there is some axial field inside the plasma source(50-100G).
1. Should different kinds of probes be used for measuring in such situations? (Shielded probes).
2. Or the IV traces obtained should be corrected by using some theory?
Thanks in advance
Bharat
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I'm Ali from Pakistan. I hv done my master with quantum plasma and also hv One publication about low temperature plasma. Now I want to work on 2D materials in relation plasma in my PhD research. Is it possible to work and study 2D materials with respect to Plasma. Can anyone here, Please help and guide me in this respect.
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Those who have been researching plasmoid and there interaction have up until now used the name plasma physics to describe the field and then bioactive plasma physics, low energy plasma physics or field plasma etc. to try be more specific and not get confused with high energy plasma physics. I would like to suggest the name Plasmoid physics which is close to plasma but not so close that they are easily confused.
ref:
Bostick, W. H., “Experimental Study of Plasmoids“ Electromagnetic Phenomena in Cosmical Physics, (1958) Proceedings from IAU Symposium no. 6. Edited by Bo Lehnert. International Astronomical Union. Symposium no. 6, Cambridge University Press, p.87
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How do you fundamentally distinguish between "Plasma" and "Plasmoid"?
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What is the physical meaning of Reynolds stress ? How to interpret it in plasma physics ?
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In the fluid momentum equation we have different terms guiding the change in momentum due to different processes. Now, what Reynolds suggested was that in case there are velocity fluctuations of particles present in the flow we can split the velocity term into two parts, one the mean velocity and other the fluctuation over the mean velocity. The convective momentum transport can now have two parts. First, is the convective momentum transport due to the mean velocity of the flow and the particles. The second one (which is, technically, the Reynolds stress term) is the momentum transfer due to the fluctuations in the velocities. To put it simply it is the mean transport of the fluctuating momentum by turbulent velocity fluctuations. This term therefore, complements fluid viscosity in the transport of momentum, but convectively.
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Boltzmann equation in plasma physics is a very fundamental equation in kinetic theory. What's the relation of the one in plasma physics and that in thermodynamics.
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Dear Nan Chu
You can follow the book entitled Physical Kinetics: Volume 10 by L. Pitaevskii & E. Lifshitz. Pergamon Press or Elsevier editions.
Chapters: III (collisionless plasmas), IV (collision in plasmas), and V (plasmas in a magnetic field).
In each chapter, the kinetic Boltzmann equation is obtained following a systematic increase of phenomena.
Amazon says the following, I unquote *:
"This volume is mainly concerned with a systematic development of the theory of plasmas, the authors being firmly rooted in the pioneering work of Landau. Corresponding results are also given for partially ionized plasmas, relativistic plasmas, degenerate or non-ideal plasmas and solid-state plasmas."
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I have read somewhere that
1. if the time scales of the phenomena to be observed are larger than the times scales of plasma oscillation and
2. spatial length scales are larger than the debye length than fluid theory is applied.
I couldnt understand the second condition, means what is the significance of wavelength of launched wave greater or lower than the debye length
please explain if anybody can ...
thanks in advance
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I agree with most answers, Dr. Purvi Kikani, the description using fluid dynamics serves to introduce a statistical description of plasmas and goes away from the single-particle picture.
In addition the fluid dynamics serves to introduce the physical kinetics formalism into plasmas, allowing to use of the Boltzmann equation.
Best Regards.
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There are three major equations in MHD plasma such as momentum equation, continuity equation and energy equation.
What is the physical significance or a description of energy equation in that ?
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Dr. Purvi Kikani, if the energy equation for the MHD is taken into consideration, then the kinetics of the fluid can be resolved.
I explain further, quantities such as the thermal conduction coefficient - kij and the heat-loss function L defined as the energy output minus the energy input per unit mass and time can be accounted for.
I attach a screenshot of the energy equation in MHD written in tensor notation.
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when we study plasma waves (plasma oscillations, electron waves and ion waves) we study perturbation in density, velocity and electric field and use momentum, continuity and poison equation to start with.
after introducing perturbation in each quantity we do linerization of non-linear (or higher order terms).
Please explain why is it necessary at all to do it? what if we do not linearlize the quantity ?
Thank you in advance,
Purvi Dave
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Dear Dr. Purvi Kikani, in Landau Lifshits 8 Vol on the electrodynamics of continuous media, in the chapter on magnetohydrodynamics, the linearization of the set of MHD equations allows solving in detail the more important modes, the Alfvén mode, and the 2 magnetosonic (mw) slow and fast modes.
Otherwise there will be a set of 9 values for the general eingenvalue equation.
This linealization allows small reversible adiabatic perturbation to the equilibrium values for the density, pressure and magnetic field H.
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I'm doing my Master Thesis on a new design for the Ionization Stage for a micropropulsion System and I would like to learn how to use some open source software suitable for the analysis of Plasma Physics.
In a previous discussion PIConGPU was pointed out. Do you think it could be suitable for the analysis of the plasma physics inside an hollow cathode?
If yes, how should I start to learn it?
If no, do you have any other suggestion?
Thank you very much for your help!
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Hi. You can find the XOOPIC code in the below link:
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I measured more than one megatesla close to H-B11 nuclear fuel during nuclear fusions. Must be confirmed.
Now it is open the possibility that the matter comprises quantified magnetic fields only
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Thank you Ijaz. The present technology has very low fusion power. Also, the tokamak can be improved a lot, our Miranda design allow ignition grade reactors using low cross-section fuel as Hydrogen-Boron-11 as we stated in our simulations. We obtained also 120 teslas easily using nonstatic magnetic fields and also 15 kiloteslas in other structures. Also, if you read our last paper you can see that if aligned nuclear fusions, more than one mega teslas can be reached, but can not be done in a Tokamak structure that would implode.
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When we are talking about any plasma system, the resonance in the system is satisfied by the condition (ω = k · v) without any magnetic field and by (ω − nωc = kzvz ) in a magnetic field. Why it happens so? What is its physical significance? Why only the parallel component contributes in the presence of magnetic field? What are the applications of this phenomenon in different branches of plasma physics starting from the laboratory plasma to the space and astrophysical plasmas? Kindly post your suggestions in the context of your expertise field. Thank you.
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Thanks. Please feel free to let us know if there is any more question.
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I am trying to implement PIC-code for the field emission simulation. According to PIC loop particles injected after calculation of charge density. But I stuck at the problem that at some points of an emitter a field could be accelerative but not strong enough to produce a charge that at least is not lesser than the electron's charge. What should be done in this situation? Macroparticle should not be injected and charge density at these points should be equal to zero or there is some condition that I am missing?
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If you don't have the condition to inject a full macroparticle at the given point, there is several things that you can do:
1. Gather charge in every step and when the condition is fulfilled (gathered charge >= macroparticle charge) create a particle.
2. Create macroparticle in every step based on some random number, that way in the long run you will have the average value correct.
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Magnetic mirrors are well known in plasma physics. In order to work, the mean free path of the charge carriers has to be at least as long as the helical paths under the influence of the B field. Therefore, magnetic mirrors exert no mirror effect on the conduction electrons in metals under usual conditions. However, ultra-pure metals at low temperature provide a mean free path of several millimeters. If the mean free path becomes longer than the dimensions of the specimen, the conduction is called ballistic.
If a magnetic mirror had the same effect on a "ballistic electron gas" as on a plasma, different electron densities in front and at the back of the mirror would result, and hence a voltage across the mirror would appear. This voltage would be built up by using the thermal energy of the electrons. Obviously, a voltage source based on thermal energy (in the absense of a temperature gradient) violates the 2nd law of thermodynamics.
I have to admit that I do not deal with details of solid state physics on a daily basis, so this is some kind of doing "armchair physics". But I would very much like to recognize the flaw in my thinking, and I didn't find publications dealing explicitely with this topic. (Usually this means that the matter is so obvious that a publication wouldn't be worthwhile.) I wrote a short paper on this subject; the quantitative result is that one could expect an open circuit voltage of the order of 200 microvolts under feasible conditions:
Any helpful comments will be highly appreciated!
PS The magnetic flux density is assumed to be limited to about 1 T (Fermi energy = 11.1 eV (iron), B = 0.5 T => path diameter = 45 micrometer), so the magnetic field can be provided by permanent magnets. Since ballistic transport is limited to low temperature, an alternative would be the use of superconducting coils.
In a laboratory setup, the entropy of the whole system would be increased by the means for cooling the device. Assuming for the moment that the effect under consideration occurs at all, a battery of such voltage sources would however, after initial cooling, keep itself cool, provided that both the thermal insulation and the electric load, located outside the insulation, were sufficient.
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Hello Stam Nicolis ,
thank you very much for your answer! I tried to avoid a question with a very long description, so I wrote just some prosa here but with a link to a text with some quantitative treatment (the graphic attached to the question shows the main result). The text also contains three sketches of possible implementations. Did you have a look at it?
The main idea is that there are two volumes of space (B0 and BM) separated by the mirror region. The boundaries of each volume are given by the borders of the metallic specimen and by the mirror. In equilibrium, the numbers of electrons crossing the mirror in both directions have to be equal which brought me to
A0 D0 P0 PA = AM DM PM PD
with the area A of the border between the homogeneous B field and the mirror region, the density D of charge carriers, the probability P of crossing the mirror based on the Lorentz force, and the probabilities PA and PD based on Pauli's exclusion principle. The indices 0 and M are referring to B0 and BM.
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Reportedly, zinc sufide (ZnS) doped with Ag or Al or Cu is the most energy-efficient scintillator: one estimate says it's 30 %, that is, for an optimized composition (doping, crystal size, etc.) a single 10 keV electron fully stopped in a thin layer of this material results in the emission of ~ 1500 photons of nominal ~ 2 eV, a total of 3 keV in photon energy, over 4 pi. I have found numerous references with data, for all kinds of scintillators (for short-emission time materials at e.g., scintillator.lbl.gov, which does not include ZnS because its long emission time excludes it from this list), but very few (and old) references to a theory (e.g., Klasen, 1947).
What is the best place to find such a theory, preferably starting with something primitive that a non-solid-state physicist can follow?
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can anyone tell me please my AlGaN-BASED samples not showing any optical properties by PL test, is it possible to test CL or EL please anyone knows about this, and can CL or EL will be able to characterize my samples or it will be the same
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What is special about decomposition products and additives of a cellulose-based electrode that helps an electric arc during welding to be less spread out? What would be a feasible mechanism linking this phenomena with decomposition product and plasma column composition during arc welding? Typical welding handbooks and references merely state the phenomena (i.e. punchy arc by H2/CO) without explaining the mechanism behind (e.g. what chemical characteristic of these two gases provide the "punch" and penetration of arc).
In general, what are the mode of action of chemical additives of an welding arc that modifies its welding penetration characteristics?
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The cellulosic electrode can create a punchy arc, therefore, higher penetration can be obtained (and that is due to the shielding gas creation from the flux which usually contains Hydrogen and Co2)
Having Hydrogen and Co2 will increase the heat input and form a deeper penetration weld pool) please take a look on the link below
I hope you got the benefit from my explanation
Thank you & good luck
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Dear friends and colleagues,
a wide dissemination of science and knowledge is of utmost importance. Thus, Gruenwald Laboratories (www.g-labs.eu) is proud to launch a new, fully open access online journal in the field of plasma physics, the Journal for Technological and Space Plasmas.
Please visit us at: www.jtsp.eu
We are looking forward to recieve your submissions. The first issue will be published in June 2018.
with best regards
Dr. Johannes Gruenwald (editor-in-chief)
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Is this a paid journal ? what is the indexing and how much time it takes to publish one article ?
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I have seen approximate formula depending on density and if it is fully or partially ionized.
I should add it to the excel table:
If there are several cases, I should like to add the cases to the excel table (I can use if inside excel formula), also visual basic can be used to include Bessel functions
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Dear Prof. Javier Luis López, interesting question. I found the following reference for general and discharges plasmas
also, I found instructive (for isotropic electron plasma in normal metals)
On the other hand, the most general equation comes in the case of an anomalous skin effect when Fermi surfaces are highly anisotropic. Please see:
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Altitudes like 1000m ; 2000m (mountains); 10000 (aeroplanes)
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Up to 10km, most capacitors work well. check the datasheet for high altitude usage.
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To design a bias circuit (constant current source) for a plasma discharge, is there an "equivalent circuit model" for the plasma itself to simulate the circuit?
I'm trying to do both: DC and RF plasma and I need a constant DC & RF current
Thank you
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The plasma discharge devices have specific I-V curve. It is in form of an S-Curve.
There are two types of models: the physical model and the behavioral model.
The simplest form of the behavioral model is the piece wise linear models. The I-V can be composed of the three linear pieces. The off branch, the on branch and the negative resistance part connecting the two pieces.
It has also a small signal linear model with R-C-L in parallel.
To operate the device into certain point it is advisable to use a consatnt current source. You can build this consatnt current source according to the measured characteristics of the tube.
It can be handled as any other electronic device.
Best wishes
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In a fusion reactor, after fusions or transmutations, some ions scapes at high speed. If a positive ion is ejected and a magnetic field is generated, then electrons would goes exactly in the same direction generating and opposite field that would reduced to 0 the generated electric field. Fortunately in the P+11B fusion charges goes in the opposite directions to maintain a 0 kinetic momentum, then the field is 0 and electrons could be at the start of fusion, but also could go coupled to ions and not generate any EM field
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About TOF, there is an FFT using phase instead of frequency: https://www-leland.stanford.edu/group/Zarelab/publinks/686.pdf
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Hi
In this reference ,plasma frequency determined by   Wp=(N x q2 /εzno x ε0 x m*)1/2
εzno   is the relative permittivity (εr) of undoped ZnO 
m* is the effective electron mass (0.28 m0)
There are some questions i want to ask:
1、Why take relative permittivity(εr) multiplied by  permittivity of empty space(ε0)?   (i find the permittivity of ZnO is 8.65)
2、The part of Ga content 1% in Table1
 N =2.18x1020 (cm-3)
m*= 0.28m=0.28 x 9.11 x 10-31=2.55x10-31
Wp=9.28x1014   (s-1)
To check the answer,I put the value into the formula:
Wp=(2.18x1020x(1.6x10-19)/ 8.65x8.85x10-12x2.55x10-31)1/2
But the result is not equal 9.28x1014 
Does anyone can set out the detailed calculation to help me to know whether i made any mistakes ?
Thanks
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Dear M.R. Hsu
You could find the following paper instructive for a generalization of what "plasma frequency in normal metals & electronic plasma" means:
SOME FEATURES OF COLLECTIVE ENERGY LOSSES OF FAST ELECTRONS MOVING IN AN ANISOTROPIC PLASMA I. 0. KULIK Physico-technical Low-temperature Institute, Academy of Sciences, Ukrainian S.S.R. J. Exptl. Theoret. Phys. (U.S.S.R.) 42, 543-551 (February, 1962)
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Please explain to me step by step method to calculate the Electron Density of a Low-Temperature Argon DC Glow Discharge Plasma using Optical Emission Spectroscopy.
This laboratory plasma is produced by DC Glow Discharge of
(i) Argon gas
or
(ii) Some other gas mixed with Argon gas
The applied voltage ranges from 300 - 500 volt, whereas the pressure ranges from 0.10 - 0.20 millibar.
I expect my Electron Temperature and Electron Density to be approximate of the order of1 eV and 10^14 - 10^15 per meter cube, respectively.
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with your resolution and expected density, it could be borderline. If you are unable to see H-beta, I'd suggest a higher lying line, like H6-H8, see PHYSICAL REVIEW E 75, 016401 (2007)
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I have obtained the behavior of potential as a function of distance from the probe, for different value of electronegativity, i.e., density ratio of negative ions with electrons. And, I find that potential profile initially decreases up to electronegativity equals one but later on it increases with increment in electronegativity. However, in literature I find that potential reduces with increment in electronegativity. How can I explain my results? Are they correct or not?
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Kashif Arshad Thank you for providing me the suitable research articles that are related to my problem.
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As can be seen in the image at https://www.researchgate.net/project/PULSOTRON-500k-SE-500KeV-THERMONUCLEAR-FUSION-REACTOR in the project log, there is an image captured during particle injection simulation. As can be seen when injecting particles perpendicular to the magnetic field (z-axis) the particles go through the reactor. I reduced particles speed and increased the injection angle but then I can not inject them in a pulsed manner.
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I have furder problems, it seems that the chamber reflects almost all incident beams. I am trying to focus on certain angles, but it seems that the chamber is good containing inner particles only.
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I've already asked a question like that and followed your advice. I started studying: Plasma Physics via Computer Simulation (C K Birdsall and A B Langdon) but I really think that I need again your help.
I will work on a java project: Starfish code ( https://github.com/particleincell/Starfish ).
I I should simulate the plasma generation inside a dischage chamber coupled with a hollow cathode.
I would need to understand how to determine the boundary conditions before starting to set up my simulation
The problem is that even in the plasma physics books I have not found the right equations or models could help me.
Do you have any suggestion?
Thank you! Tommaso
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The best way is visit someone who has experience in this code. Otherwise, you will take lots of time and energy!
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I am looking for physics-based measurements that can be performed in the edge plasma (upstream, not at the divertor) that yield the separatrix position or some boundary for it. Some of the methods I am working on:
- measure the profile of plasma potential, find the peak
- measure density or ion saturated current fluctuation, find zero skewness (inner boundary)
- measure the profile of electron temperature, electron density, heat flux etc., fit it with a "broken" double exponential and find the breaking point (outer boundary)
- measure the profile of poloidal velocity (cross-correlation of poloidally spaced probes, Er x B drift etc.) and find the zero
Some of the methods I have found (some thanks to the answers below):
- in H-mode, fit the pedestal Te or ne profile with the tanh function and find its center (can optionally be corrected for some fraction of the SOL width) [G. Porter, Physics of Plasmas 5, 1410 (1998)]
- (specific to field reversed configurations with a weak external plasma source) modulate the plasma source at a known frequency and measure the floating potential profile with a Langmuir probe; the region where the frequency amplitude goes down suddenly is the magnetic separatrix [answer by S. Cohen below]
- assuming pressure balance along the field line, map divertor pressure measurements to upstream (at the divertor, the strike point position is known, e.g. Eich function fit, maximum heat flux etc.) and match it to upstream pressure profile (this can also be done with the floating potential, electron temperature, heat flux...) [C. K. Tsui, Physics of Plasmas 24, 062508 (2017)]
- develop some really specialised probes [K. Uehara et al, 2006 Jpn. J. Appl. Phys. 45 L630]
- use the power balance criterion (AKA Stangeby's two-point model) to calculate the separatrix temperature, then find it on any measured Te profile [H J Sun et al 2017 Plasma Phys. Control. Fusion 59 105010]
I am open to any suggestions, links to previous research, or your personal experience (whether you've encountered the problem of not knowing exactly where the separatrix is, whether you think it's worth addressing etc.).
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Guanghui Zhu Thank you for the suggestion. Could you please elaborate it? I'm not sure how I can infer the separatrix position from radiation distribution or temperature and density profiles. In both cases, I think that I'd have to make some additional assumption, such as "upstream separatrix temperature is 70 eV" supported by the two-point model.
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My calculations with fixed probe potential for electronegative plasmas show that sheath thickness enhances with an increment in positive ions' temperature for fixed temperature of negative species, i.e. electrons and negative ions. But, I am not getting the reason why it is so.
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If you look at the total equation for the Debye length, which basically determines your sheath thickness, as you can see here: https://en.wikipedia.org/wiki/Debye_length
you will see that a larger value of T_i will increase the Debye length and that is the reason why the sheath thickness increases for a fixed potential.
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Rogue waves are an important topic in water waves, plasma physics, nonlinear optics, Bose Einstein condensate and so on
How can we predict a rogue wave?
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Are you interested in theoretical aspects? If yes, decouple your system in the form of a dinNPDE. Apply preferably numerical simulations to see the wave amplitude behaviours, and so forth. Have a needful comparison with the latest reports on it.
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I have read in a lot of papers related to numerical plasma physics that a separate equation named "Energy Balance Equation" (that looks a bit similar to continuity equation) is also taken under consideration for electrons only.
It is clear that the continuity equation gives the value of electron/ion density at the grid points and the Poisson equation gives the value of potential and electric field at the grid points. These Poisson-Continuity equations work together giving values to each other.
Could somebody explain me the use of Energy Balance equation in the simulation. I am not sure about what is calculated solving the Energy Balance equation.
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It is similar to the energy balance of lightning in the sky.
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What is the physical difference between the two and how are they used to study electromagnetic waves in parallel and perpendicular AC electric fields.
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As is known, you can use a bi-maxwellian distribution as soon as you have a temperature "anisotropy", for instance a difference between the perpandicular (Tr) and paralelle (TL) temperatures to the direction of the electromagnetic field. To use such distribution, you can simply define a transversal and longitudinal component of the velocity (Vr and VL) in order to put in the exponential term of the maxwallien distribution the sum of the square of their ratio (i.e. something like that: exp( -(VL**2/(c*TL) +Vr**2/(c*Tr))) where the product c*TL or c*Tr has the same dimension as a velocity. I hope that this short reply corresponds to what you want.
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In some lecture report[1] they say Zonal flow stands for the mode with toroidal/poloidal mode number n=m=0 mode in plasma physics. So the n=0, m!=0 Geodesic Acoustic Mode (GAM) is not Zonal flow. But in other paper[2][3], they say GAM is also a kind of Zonal flow. So who is right and who is wrong? Exactly what is zonal flow in plasma physics?
[2] L.W. Yan et al 2007 Nucl. Fusion 47 1673 Three-dimensional features of GAM zonal flows in the HL-2A tokamak
[3] L. Lachhvani, J. Ghosh, P. K. Chattopadhyay, N. Chakrabarti, and R. Pal, “Observation of geodesic acoustic mode in SINP-tokamak and its behaviour with varying edge safety factor,” Phys. Plasmas, vol. 24, no. 11, 2017.
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Dear Nan Chu,
In my view, they are nor right or wrong, it is a subject of definition. It looks like you have a tokamak in mind. Toroidal and poloidal rotations in tokamaks are analogs of the zonal flows in the atmosphere, while oscillations of plasma pressure are analogs of GAM.
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Thank you for spending your precious time:
I am working on GOLEM TOKAMAK dataset for disruption prediction using machine learning and i found the below features play a major role in disruption prediction so,below i have attached a set of features but i find hard to download the signals because i couldn't identify which data suites the exact feature mentioned
plasma current - Ip (available)
Total input power - available
mode locked amplitude - no idea
plasma internal inductance - no idea
plasma density - no idea
poloidal beta - no idea
so,could anyone please suggest me a which data signal i have to select or from which signal i have to derive the above feature.herewith i attached the page for dataset download.
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Using data-driven methodology, we exploit the time series of relevant plasma parameters for a large set of disrupted and non-disrupted discharges to develop a classification algorithm for detecting disruptive phases in shots that eventually disrupt. Comparing the same methodology on different devices is crucial in order to have information on the portability of the developed algorithm and the possible extrapolation to ITER. Therefore, we use data from two very different tokamaks, DIII-D and Alcator C-Mod. We focus on a subset of disruption predictors, most of which are dimensionless and/or machine-independent parameters, coming from both plasma diagnostics and equilibrium reconstructions, such as the normalized plasma internal inductance i and the n = 1 mode amplitude normalized to the toroidal magnetic field. Using such dimensionless indicators facilitates a more direct comparison between DIII-D and C-Mod. We then choose a shallow Machine Learning technique, called Random Forests, to explore the databases available for the two devices. We show results from the classification task, where we introduce a time dependency through the definition of class labels on the basis of the elapsed time before the disruption (i.e. 'far from a disruption' and 'close to a disruption'). The performances of the different Random Forest classifiers are discussed in terms of several metrics, by showing the number of successfully detected samples, as well as the misclassifications. The overall model accuracies are above 97% when identifying a 'far from disruption' and a 'disruptive' phase for disrupted discharges. Nevertheless, the Forests are intrinsically different in their capability of predicting a disruptive behavior, with C-Mod predictions comparable to random guesses. Indeed, we show that C-Mod recall index, i.e. the sensitivity to a disruptive behavior, is as low as 0.47, while DIII-D recall is ~0.72. The portability of the developed algorithm is also tested across the two devices, by using DIII-D data for training the forests and C-Mod for testing and vice versa.
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I have designed a thin torus to be filled with hydrogen or deuterium plasma accelerated to 80 kA.
This is not a standard tokamak design that have only one confination coil.
The problem is when going the particles inside it oscillates forward and backward the torus centre increasing the amplitude until the particles scapes.
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Well Landau-Lifshiz Textbook Vol 8 has a chapter on magnetohydrodynamics, They discuss a toroidal plasma problem, I think... read the chapter, obtain all the equations there, find a good fellow programmer and then work very hard on any question regarding plasma confinement... the chapter is a beautiful masterpiece joining magnetism and hydrodynamics.
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Dear all,
Kindly tell me as how to use FEM in dusty plasma physics. Any paper or book related to the same if you have with you please let me know.
Regards
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Dear Wahid,
Thank you very much for your advice.
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How we can explain the inverse relation-ship between plasma density and Debye length physically ?
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The explanation is not complex. Higher the density, the charge in unit volume is higher, therefore a smaller displacement produces a larger screening field.
Assuming the Debye length a measure of the equilibrium displacement, you have the answer to your question.
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I have seen in most of the plasma physics textbooks the temperature versus pressure graph as shown attached with this question.
The graph as attached in this question is useful to explain the transition of a non-thermal plasma to thermal plasma. For non-thermal plasma, Te>>Tg whereas for thermal plasma Te~Tg.
The attached graph with this graph is not a real plot. It was sketched for understanding by Prof. Alan Howling. Did anybody try to obtain it through calculations ?
I would be happy for your answers and interested to obtain it with some graphical softwares like MATLAB.
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You can derive the ratio of Te/Theavyparticle via the momentum and energy law as it was originally done by Maecker & Co. Then you obtain a quadratic equation depending on E/p. In other words: If it deals with a discharge then the pressure is not enough and you have to add E (electric field). Te/ThP then depends on repsective cross sections which builds the bridge to the species that you use. The respective equation can also be found in my habilitation (chapter 5) including a list of relevant plasma systems against which I verify the equation (on basis of measured data)
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It is known that high energy gamma photons can decay into electron-positron pairs in a strong background field via the multi-photon Breit-Wheeler process. This real photon is first emitted by an energetic electron, therefore this is a two-step process. There exist also one-step process, where the intermediate photon is virtual, thus one electron can directly create the pair in a strong laser field. For the trident production rate I found formulas in the literature, which is implemented in EPOCH for instance, but in the code the energy of newly created particles is zero. In the case of two-step process it is clear that the total energy of pair is equal to the photon energy, but I could not find any clear expression for this initial energy in the case of trident. I think it is assumed that their initial momentum is relatively small and their recoil effect is negligible, that's why it is approximated by zero in order to reduce the computation in PIC codes. However, I could not find any paper supporting this statement. Can someone help me in this ?
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Thank you for your answer! I agree, the energy of pair should be equal to the photon energy, but in the trident process the photon is virtual and it is not clear to me what is the energy of that virtual photon...
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To generate a high power discharge usually a capacitor over a coil is done, but to make it at high power a great capacitor must be used and as long that frequency is inverse proportional to square root of inductance and capacitance, large capacitors should lower the frequency.
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It seems possible to drive the off-the-shelf $40 microwave oven 2.45 GHz magnetron in a kind of pulsed mode for generating "short" bursts of CW. In some wireless power transmission experiments it was used to create low-cost a few kW sources. It could be done by modifying the standard oven power controller and AC power supply by adding a few extra circuits to enable a sort of pulse modulation. However, this approach requires a lot more mechanical work to channel the magnetron energy into a waveguide or coax to get the power out. To increase output power a bank of magnetrons could be used. Although control and synchronization of several magnetrons would be tricky.
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Our fusion reactor Miranda have dozens of parameters to adjust to obtain reactions.
Our simulator uses an easy algorithm to simulate our models running 16 threads but it is difficult to change all the parameters so we have few data to feed the learning algorithm, so we need a neural network with a very fast method that learns with few samples.
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Use Extreme Leaning Machine, no iteration. One step learning.
Simple description available:
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I heard that arc discharge with 2kv is required to ablate the surface and ionize it but i dont know the relation. i hope that this relation will help in knowing the amount of energy required to ablate various propellants
                            thank you 
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I think it depends on how the energy delivery to the teflon surface. How is the structure of the discharge device? I think the literature in Prof. Mohamed A. Abd Al-Halim can provide many useful information. Moreover, you can also search the other articles on the ablation controlled arc.
Best regards
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During my plasma treatment I observe increase in surface temperature on powered and grounded electrode in CCP-RF low pressure configuration.
At increased RF power, temperature of powered electrode increases.
In my case electron neutral collision frequency is higher than applied rf frequency i.e. 13.56 MHz. Thus ohmic heating is dominating.
Please explain me how to calculate the surface temperature on both powered and grounded electrode ? Any theory / equations help if we know the density and temperature of plasma ?
Thanks in advance,
Purvi Dave
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Please see Radio-Frequency Capacitive Discharges Raizer, Yuri P., Shneider, Mikhail N., Y ISBN 10: 0849386446 / ISBN 13: 9780849386442 Published by CRC Press, 1995 for theory and technology of capacitively coupled RF discharges. Another relevant book is Plasma Chemistry, by Alexander Fridman, Drexel University, Philadelphia, 2008.
Ohmic heating is a rough zero order estimation. Near electrode processes play a key role in electrode heating of CCP-RF discharges. Thermal flux to the electrodes may exhibit non linear dependence on pressure and power density.
The difference between grounded and powered electrodes may rise from the difference in current densities on the electrodes - some grounded parts of your chamber may also work as electrode decreasing current density on the grounded electrode.
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I was wondering if there are free access to data for plasma physics online which can be analyzed and further work with it computationally as well. I'd glad if anyone could mention possible project ideas for undergraduates related to plasma physics.
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A lot of useful он Databases for Atomic and Plasma Physics
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I am trying to search for a topic in plasma for my project and I am quite new to Plasma Physics. So if you could also suggest me on how to start with this topic,it'd probably help me a lot.
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You should go through some basic books (by reputed authors and publishers) as follows:
1. Chen, F. F., Introduction to Plasma Physics and Controlled Fusion, 2nd ed. (Plenum, New York, 1984).
2. Nicholson, D.R., Introduction to Plasma Theory (Wiley, USA, 1983).
3. Bittencourt, J. A., Fundamentals of Plasma Physics (Springer, New York, 2004).
4. Bellan, P. M., Fundamentals of Plasma Physics (Cambridge, UK, 2006).
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I am unable to understand the origin of components of CC P-RF sheath equivalent circuit components (resistor, capacitor and diode) and that of bulk plasma (resistor and inductor).
I am not getting any simple words explanation of physics over there. Can someone please explain me or help me with suitable literature ?
Thanks in advance.
with kind regards,
Purvi
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The rf sheath( its thickness) forms the the capacitor.The equivalent resistance is just that resistance which accounts for the power lost due to the ion current flowing across this rf sheath. The diode is due to the dc voltage which prevents more electrons than ions current crossing the sheath. Another way of looking at this is that the ions are much more massive than the electrons.
The plasma its self is so much more conductive that one does not normally include it except for the inductive sheath in an ICP and other heating effects. For more details see : J.H. Keller and W. B. Pennebaker, "Electrical Properties of RF Sputtering Systems", IBM Journal of research and development, Vol. 23, No.1, Jan 1979
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What exactly changes when we use 40 KHz, 13.56 MHz or 2.4 GHz plasma source for plasma surface activation of polymers at low pressure in CCP-RF type plasma ?
Why 40 KHz gives better results compared to 13.56 MHz plasma ?
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When you go to GHz (microwave discharges), the period of the electric field is too short for any particles to gain some momentum - even the electrons just "shake" and don't move much across the volume. These discharges are then closer to equilibrium having the temperatures (electron, excitation, vibrational, rotational and kinetic) rather close compared to the lower frequency.
When exciting with MHz (RF), the electrons now follow the electric field, usually managing to move across a substantial part of the reactor, forming sheaths at the edges. The ions, on the other hand, are still not able to follow and usually are considered static. The plasma is usually "on" the whole time.
In kHz, the period is already so long, that the plasma often quenches for some part of the period. The ions are now able to follow the field, but often the recombination is faster than the drift (at least for high pressure).
As for your last question - "Why 40 KHz gives better results compared to 13.56 MHz plasma ?" - to answer this for a particular case, serious effort is required. Often you need to combine extensive plasma diagnostics combined with modelling and look for correlations with the activated sample properties - making enough results for several papers. Here, the answer is almost never obvious.
If you have good results at such low frequency, I would check for thermal damage of the samples at higher frequencies, or try to arrange the treatment not be the "glowing" plasma but the afterglow.
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Thank you
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When laser light passes through the plasma it gets absorbed in it through inverse Bremesstrahlung process. In this case absorption coefficient is directly proportional to the plasma density and inversely proportional to plasma temperature. An increase in laser intensity increases the plasma density and temperature. But at higher temperature electron ion collision frequency decreases, which limits the laser absorption in plasma. This process creates a saturation after a certain laser intensity. This can be seen in one of the paper given below
Laser and Particle Beam 30 621 (2012)
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We consider small perturbation in plasma to understand the concept of plasma oscillation.
We take perturbation in velocity, density and electric field.
que-1 how do we create this perturbation (with what frequency, voltage and how ?). want to understand with physical example.
que-2 we consider small perturbation, how can we quantify this ?
que -3 what will happen if we remove the given perturbation ?
Thank you in advance,
With kind regards,
Purvi
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The "small" perturbations mean only the lowest-order harmonics on the plasma parameters are excited. The squares, products, or higher-order contributions from the perturbations are negligibly small. It is immaterial of the fact whether "local" or "global" equilibria are considered for the next step of homology transformations.
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The problem is that the isolators parts of coils heat must be removed.
Isolation materials have low power transmission coefficient (about 0.6-2.5 W/mK) with respect copper (>400W/mK).
Unfortunately attaching directly copper parts to vacuum chamber wall would shortcircuit the internal coils
This problem was detected during the thermal design of Rita and Patricia fusion reactors
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Using water as a coolant one usually is able to prevent excessive heating of the coolant simply with adequate feeding. Limitations may arise from high dielectric constant of water and chemically induced electric conductivity of the water used. If those limitations are serious water can be replaced by transformer oil. But thermal properties of oil are nowhere near so good as that of water.
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I've known that one of the unresolved problems is the Coronal heating problem and there are already many theories to explain the illogical temperature at the Corona. I need to know what are the other problems in the field of Solar Physics and what are the challenges to explain these problems?
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Mohamed,
Try as a potential starting point, the article makes many good points concerning the class of the problems you may encounter. To astrophysics in general I would add the coronal heating issue, the galactic halo velocity problem, the pioneer anomaly, and even the angular velocity of each sub-ring of Saturn's rings. From a chemistry point of view (rotational-vibrational energy coupling, etc), there seems to be a coupling of energy of some sort that applies to all of these issues. Like many good questions, yours could be the start of a lifelong conversation.
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For example: He-air chemical reaction involved.
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BOLSIG+ gives you the value of Reaction Coefficient (unit m^3/s) which has to be multiplied with neutral gas density and electron density.
Source= rate_coefficient * neutral_gas_density*electron_density
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Non-Linear waves propagating in plasmas
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It implies the shape conservation property of the propagating KdV soliton. In other words, the plasma perturbations propagate in such a way that the strength of the nonlinear wave steepening is always proportional to the linear dispersive wave broadening on the spatiotemporal scales of our observation.
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In some conditions we take average K.E. if electron in plasma as 1/2 KT and sometimes we take just 'KT'.
When should we consider what and why ?
Thank you in advance,
Purvi Dave
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It depends on the number of velocity dimensions you are considering in your system. For each dimension you have 1/2 KT. Therefore in 1D you should use 1/2 KT, in 2D KT and in 3D, as usual in plasma, it is 3/2 KT.
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Hello Community,
I am working with a CH4/H2 Plasma in a cold-wall reactor. If I use conducting substrates (like metalls) there is a homogeneous plasma visible above my substrate (roughly 1-2 cm aboce the surface of the substrate). Now if I use non-conducting or semi-conducting substrates (GaN on sapphire susbtrates) there is a clearly visible "hole" in the plasma just above the substrates surface. With my humble knowledge about plasma physics, I know that the non-emitting parts of the plasma mean that there are just positive ions and no more electrons (plasma sheath).
So my question is: what is the reason for "hole" above my substrate and what exactly happens there with the precursor molecules?
I would suggest that, because of the non existing potential drop between the substrate and the electrodes, there is no acceleration of positive ions torward the substrates surface there. But what kind of molecules/atoms define this region above the substrates surface?
Is there just a huge plasma sheath and thus I see no emission or is there simply no plasma at all and no decomposition takes place in this region?
Maybe some of you already stumbled over a similar problem.
With best regards
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Hi Pieter,
Thank you for your assessment. It could be that there is absolutely nothing happening there. But somehow I doubt that there is no dissociation due to impact ionisation. Maybe it is just a a non emitting area of the plasma
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plasma in physics contains two types especially Non-thermal plasma...what is it?
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Thank you dear ...saeed
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What is the difference between plasma blood and plasma physics?and mechanical is similar to them???
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Blood has two components - the clear liquid and the corpuscles/cells entrapped in it. The clear liquid was named "plasma" by the famous Czech medical scientist (physiologist), Johannes Purkinje (1787-1869).
In 1927, Irving Langmuir- the American chemist  was exploring ionized gases (i.e. gases subjected to strong electric field to knock out the electrons from gaseous atom). He used the analogy of blood, with the ions being the corpuscles and the remaining gas being a clear liquid and named the ionized state of a gas as plasma. Thus, this name prevailed.
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Hello, everyone, I want to know, how to interpret the results of correlation coefficients. I have noted its explanation from the links
Correlation coefficients whose magnitude are between 0.9 and 1.0 indicate variables which can be considered very highly correlated. Correlation coefficients whose magnitude are between 0.7 and 0.9 indicate variables which can be considered highly correlated. Correlation coefficients whose magnitude are between 0.5 and 0.7 indicate variables which can be considered moderately correlated. Correlation coefficients whose magnitude are between 0.3 and 0.5 indicate variables which have a low correlation. Correlation coefficients whose magnitude are less than 0.3 have little if any (linear) correlation.
But I don't know whether I can use this in Plasma physics statistical study or not?
any help will be appreciated. thanks
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Dear Abdur, Please note that the value of the correlation coefficient is very much function of the sample size. A value of 0.63 may be just sufficient to be significant for the sample size of 10 or 0.7 value of r will be significant if n=8. In view of this to attach importance without considering the pairs of data involved is meaningless. As far as  I understand as a statistician is that significant r means there is a linear relationship between the two variables x and y considered. Second, if you are interested in any predicting model that is interested in predicting y given x  then r should be significant first and then should be as high as 0.8. R^2 is always used for interpreting the results like 0.3 significant r means only 9% of the variation in y is due to x and 91% variations is coming due to many other variables. So please indicate why you want to study the correlations, only to know the relationship between various variables considered or you want to proceed further from there? I feel getting significant r is one thing and then to go for prediction is second thing. A high significant r (more than 0.8) will enable you to predict y given x with a meaning attached to it is that it can only explain about 64% or more variation in y given x.  
Your question is very general cannot be answered well unless you provide more data like X (Indenpendent variable), Y( dependent variable), n, r and its significance. You may be aware that there also exist spurious correlations like increase in sales of news paper and increase in crime rate of a given area. So, before you calculate r there should be some scientific basis or reason to believe that X and y are correlated. 
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Please help, it says that ECR plasma has bombardment effect, but where does the kinetic energy of ions come from? Does the substrate has to be negatively biased? I
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Thanks for the help. 
So the kinetic energy comes from the sheath potential and ambipolar diffusion of ions and electrons
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I try to find a relation between Power (P), Argon pressure (ppm) and probably distance (cm) between cathode and plate so as to have maximum ionisation of gas.
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you have to monitor the discharge current to know something about the ionisation, and also monitor the deposition rate, which would give an idea about the bombardment occurring on the target, the sputtering yield, and eventually the deposition rate that is achieved. You should know the film thickness that has been developed on the substrate, by meauring it accurately, either with a film thickness monitor insitu, or externally with an off line thickness profiler.
At a fixed power, and a substrate to target distance, an increasing pressure should result in increasing deposition rate, and ultimately beyond a certain pressure, the deposition rate would go down due to enhanced scattering.
An appropriate pressure for routine thin film deposition would be around 5 to 15 mTorr.
Actually DC mangnetron sputtering allows you to strike a discharge at lower sputtering ressures of 5 mTorr, and such low pressures many a times with different materials help in obtaining a better quality thin films.
There is a lot of literature available, and many good books are also there which I think you should read and consult to understand the complex inter dependence of sputtering parameters.
K. Sreenivas 
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I am currently using for the first time ICP-AES and we have encountered some ignition problem, the plasma went off suddenly and since then we haven't been able to ignite it, we get a message popping up on screen , which say magnetron voltage is too high. Can someone please highlight some of the problem they have encountered while using Agilent ICP-AES 4200 and how did you solve them?  
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We have a Perkin Elmer ICP-OES (5300 DV). I was warming up the ICP to analyze the samples and the torch was on for atleast 45 minutes. All of a sudden it went out. I tried starting it again but it won't. When trying to start the torch, I could see a spark for 1-2 seconds, but no sustained plasma. I replaced the torch, cleaned the RF coil and also checked the argon flow but in vain. Am missing out on something? Any suggestion would greatly help. Thanks!
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For plasma with Radio Frequency(RF) heating, dose higher electron density have better RF heating effect?
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The heating process depends on RF wave penetration depth into the plasma, which, if no magnetic field is applied, can be evaluated in planar incident wave approximation with Appleton equation, knowing the electron-neutrals&ions collision frequency and plasma frequency, which is related with electron density. The reflected power can be calculated numerically and sometimes evaluated analytically, also it can be measured. Then the efficiency can be derived from the absorbed power. Also the heated volume is related with penetration depth value. Here I don't mention the heat exchange in plasma via few mechanisms, which are significant for high energy density applications.
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Hello.
I've read some article that the inverse bremsstrahlung is the process that a free electron absorbs a photon while it collides with an ion, so it is 3-body process.
But I don't know how it is physically explanined. Why the electron that is in collision with the ion can absorb the photon?
And I would like to know the relationship between the laser energy and the plasma electron density. I've also read the following relations.
1. If plasma angular frequency wp < laser angular frequency w : the plasma is transparent for the laser.
2. If wp = w : the plasma becomes a perfect mirror.
3. If wp > w : the plasma becomes a good laser absorber.
I can understand the 1st case as it is easily proved in a undergraduate level plasma physics course. 2nd case...is what I may accept.. But 3rd case...how can it is physically explained?
Thanks for reading this and I look forward to get any response.
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The third points depends on the cross section of the process that increases with the frequency, The optical properties of a material, as well as that of a plasma depends on the dielectric constant that is a complex quantity, where the imaginary part is the conductivity of the material. Analyzing the response of the plasma to the frequency, Higher the conductivity at a given frequency, higher the reflectivity. All the material have response frequency that for a plasma in wp. The conductivity has a bell shape as a function of the frequency, with a maximum around wp. Reverse bremsstrahlung happens when the plasma is transparent, and because its cross section grows with the frequency, it explains the third point.
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The project theme is very interesting and I would like to learn the ionization process which takes place when the high energetic particles (electron/proton) enter to our inner magnetosphere-ionosphere-atmosphere system. I am doing the link between this ionization process and atmospheric electric field changes over south polar stations,  so that either this ionization creates a localized capacitor system at middle atmosphere or what kind of changes been expected.? 
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Dear Prof. G.F. Remenets,
           Thank you very much for your timely help, I will make use of these articles to improve my knowledge. thank you 
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I'm working in the plasma physics and trying to calculate the thermal conduction time or speed.
The plasma treated has cylindrical symmetry surrounded by the dielectric material.
Right now I need to calculate the time the energy or heat takes to move from the axis of the plasma to the wall with the given thermal conductivity.
I guess the time is function of not only conductivity but also temperature difference between two points thus let's assumed that the axis temperature is Te while dielectric is at room temperature..
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Book: Laser and electro-optics, Christopher C. Davis, 2nd edition, section 10.2, page 252
t~(D^2) /(cl)
D:diameter of tube
c:mean velocity of gas particles
l:average distance traveled by a gas particles between collisions.
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In plasma configuration, plasma is generated by top/bottom electrode and consists of positive ion and electron. And ion-electron recombination time is very short. So my question is that how can we get ion-electron recombination time or duration in the case of SF6 plasma? For designing my experiment, ion-electron recombination time of SF6 is quite important factor but I have a difficulty in this problem. I want to get some information, comments or tips about it. Thanks
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Microwaves are sometimes successfully used for such measurements. Requirements are: proper electron density and dimensions of plasma, comparable with the probing signal wavelength.
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see the surface wave plasma device of Prof. Kousaka, nowat Gifu Univesity
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good question
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In a DC sputtering diode system, the positive ions follow the electric field direction till they hit the target to eject materials, while the electrons move in the opposite direction.
- how do the electrons reach the anode if the substrate was not conductive?
- the net current direction should be in the same direction of the electric field, where is the closed path of ion and electron currents?
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electron sputtering needs really high kinetic energies in the order of several 10's of keV, so "breaking" the glass is close to impossible in your case, I would say. They should form an electron rich sheath on the surface of your glass instead.
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We are planning experiments that will involve hydrogen-boron plasma reacting with beryllium electrodes. Since very high current densities are involved, we are interested to see if any BeB compounds that are formed will have good electrical and thermal conductivity once the current heats them up.
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Dear Eric,
here are some values for electrical resistivity.
As for BeB4: 1.1 * 10^7 Ohm*cm @ T = 300 K 
As for BeB6: 1.1 * 10^7 Ohm*cm @ T = 300 K
Sources:
For other BeB compounds, you could like to have a glance at the monographic papers:
Samsonov G. V., Serebryakova T. I., Neronov V. A., "Boridy", Moskva Atomizdat 1975
Serebryakova, T. I., V. A. Neronov, and P. D. Peshev. "Vysokotemperaturnye boridy." High-Temperature Borides), Chelyabinsk: Metallurgiya (1991).
With warm regards
Andrea Di Vita
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I need the cold plasma for decontamination of the medicinal plants.
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Hello
Thanks a lot for all your answers.
regards
shabnam
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Modified Boltzmann plot is one of the widely accepted method for electron temperature estimation in atmospheric pressure plasma jets. Since, this is based on the relative emission intensities existing in the optical emission spectrum of  a particular plasma, I wanted to estimate electron temperature for Argon plasma jet. Using 14 emission lines, I obtained the value of electron temperature around 0.35 eV.
I used the same spectrums to calculate electron temperature using collisional radiative model. The electron temperature is observed to be much higher than obtained using Modified boltzmann plot. 
The plots of both methods have been attached here.
Can somebody help me why there is so much variation between the electron temperatures of modified boltzmann plot and collision radiative model although I use same spectrums for calculation ??
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Even if you call both quantities electron temperature, you are talking about two different things. It is not clear what you call collisional radiative model approach. I thing that you assume in both cases a Boltzmann distribution for levels and Maxwell distribution for electrons. This assumption is often valid in atmospheric plasmas. In flowing plasma this assumption should be taken carefully, especially for noble gases. The presence of high energy metastable (in argon is about 10 eV) not observable in the emission spectra, is a source of non-equilibrium. Both electron and internal distribution are not Maxwell/Boltzmann and therefore the concept of temperature is misleading.
Look at 
Kinetic processes for laser induced plasma diagnostic: A collisional-radiative model approach by LD Pietanza, G Colonna, A De Giacomo, M Capitelli - Spectrochimica Acta Part B: Atomic Spectroscopy, 2010 http://www.sciencedirect.com/science/article/pii/S0584854710000625
and 
Boltzmann and master equations for magnetohydrodynamics in weakly ionized gases by G Colonna, M Capitelli - Journal of Thermophysics and Heat Transfer, 2008 http://arc.aiaa.org/doi/abs/10.2514/1.33479
to see examples of non equilibrium distributions.
Typical eedf in post discharge in Ar present a long plateaux up to 10 eV due to the cooperative effect of superelastic (de-excitation of ar by electron impact)  
e(E) +Ar* > e(E+E*) +Ar
and elastic collisions. 
The Boltzmann plot technique therefore gives you the level temperature, the second one (still and excitation temperature) gives you the temperature of a Boltzmann connecting the zero energy and the emitting level. The difference in temperature shows that you have a plasma in recombination regimes, where the population of the level is not determined only by the excitation from the ground state, but also from recombination e+Ar+, which produces a plateaux also in the level distribution
see for example
Coupled solution of a time-dependent collisional-radiative model and Boltzmann equation for atomic hydrogen plasmas: possible implications with LIBS plasmas
G Colonna, LD Pietanza, M Capitelli - Spectrochimica Acta Part B: Atomic Spectroscopy, 2001 http://www.sciencedirect.com/science/article/pii/S0584854701002233
 and the book
M. Capitelli et al. Fundamental Aspects of Plasma Chemical physics: Kinetics
Hope it helps
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someone who does the research about plasma control  may know the answer
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Dear Yanli Peng,
high temperature plasmas can only be achieved when isolated from any materials. Otherwise the contact to a structure material will cause a too strong cooling of the plasma usually via impurities coming from the wall.
For the confinement 2 possibilities exist: like in the sun gravity or magnetic fields. At earth we cannot succeed with gravity but do the nect best using the inertia of a dense material while heating up (inertial confinement). The second option is a megnetic confinement of the charged particles. Due to the nature of the game the charged particles can move rather freely along the magnetic field lines while the perpendicular motion is in zero approximation inhibited by the Lorentz force. Therefore closed magnetic field lines are used to confine the plasma. Closing the field lines required a bending of the field lines.
A transport perpendicular to the field lines can happen via collisions only or by drifts in electric fields or curved magnetic fields. In any case the perpendicular transport is slow compared to the parallel one. Nevertheless, the alignment of magnetic field and vacuum vessel is not perfect and somewhere exists an outermost magnetic field line which hits the vessel wall. Particles stream with high velocity parallel to the fiel line and bombard the wall at rather high energy. The still existing perpendicular transport causes a continious filling of this field line keeping the process going.
Since this cannot be avoided it is preferable to introduce a defined contact point of plasma and wall. The limiter is a protruding wall element which can withstand high particle fluxes at rather high energies. This is supported by shallow inclination angles between wall and magnetic field to increase the area of impact therefore, reducing the incoming power density. Furthermore limiters are cooled to get rid of the energy as soon as possible. Still the incoming power density can be easily above the material limits. A limited life time due to erosion is also a concern. But even without these effects the limiter configuration has a substantial disadvantage especially when made from high Z materials: the sputtered material enters the plasma and can caus tremendous radiation losses, cooling the plasma even up to a plasma collapse.
This can be overcome by the divertor concept. Here the outermost region of the magnetic field consists of open field lines. These field lines guide the particles outside a certain plasma radius away from the confined region of closed magnetic field lines. The open field lines are connected to limiting wall structures (divertor). The  geometry is chosen in such a way that the connection length of the open field lines between the area where they are filled by the plasma to the wall structure becomes very long (~100m). This is a key feature of the divertor concept  - separating wall contact area and confined plasma - and allows the plasma to cool down.  The wall structure itself is in large fusion devices separated from the main vacuum chamber via a narrow throat. This throat allows for high neutral densities inside the divertor chamber cooling the incoming plasma further. A cold high density plasma exists in front of the divertor wall (divertor plates). The wall material can better cope with high densities than with high temperatures. This rather cold high density plasma in front of the divertor plates acts as a buffer for the material and also prevents sputtered impurities to reach the confined plasma.  This is a key feature for future fusion devices. Otherwise the impurities will cause a radiation collapse of the confined plasma. The inclination angle between magnetic field lines and divertor plates is also kept small to allow for a wide power spreading.
Hope this explanation helps.
Best regards,
Werner Müller
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Why the plasma ingredients become degenerate due to the influence of Pauli-exclusive principle and classical statistical assumptions is break dawn ?
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Dear Dr. Behnam Farid,
Thank you again.·
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I want to use RIE to etch GaN, I think I should use Cl2 and BCl3 but I need to know about the range of plasma power and working pressure.
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I used Cl2 and Ar together. Here is the recipe:
chamber pressure ~ 20 mTorr
DC signal reading: 600
Power: 175 W
Cl2: 20 sccm
Ar:6 sccm
In order to etch 900 nm GaN/Al(6%)GaN, you need 8 min around. But you should etch for few min then wait for few min then etch for few min to avoid over heating. For 900 nm, 3 min etch and 2 min wait 3 min etch 2 min waiting then finally 2 min etch worked fine for me.
Also you should clean the chamber before you start etching for about an hour with this recipe:
Cl2/Ar   4/46 sccm  ,, 300 Watts, 60 min, 20 mTorr (or any value).
Then you should run a conditioning (same recipe as etching) for the time needed for actual etch. In our system it was difficult to control CL2 flow, so after conditioning I completely turned off the CL2 flow. Whatever left in the pipe line, it was enough to use for etching.
I hope this recipe work for you, too. You may need to optimize the values for your case.
Good luck.
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in our lab, TaN electrode is deposited using DC sputter system and fabricate MOS capasitor composed of ALD-high-k thin film. However, reproducibility is not good specially at I-V measurement. so we guess because of plasma damage in sputter system. Is it possible? I want to ask you for advice.
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TaN shows metallic behaviour but the specific resistance is highly influenced by the sputter process conditions (pressure, power, N2/ratio) and base pressure and O2/H2O residual gas pressures. Furthermore the substrate and temperature of deposition have a large impact. If you sputter onto an oxide (e.g. SiO2) TaN will form Ta2O5 and your resistivity will go up. On some substrates you will form amorphous TaN layers, some substrates will give you polycrystalline or microcrystalline structure. This all has influence on the film properties. If you see variations in resistivity and all circumstances are the same I would guess the vacuum integrity (H2O/O2 levels) or the temperature control in vacuum are the most likely causes. For thin layers <150nm you can get very erratic behaviour because of defects (particles, pinholes, etc).
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The charged particled trapped in the Van-Allen belts around Earth, maybe they affected by the natural Earth's rotational or wobbling motions and their distribution get disturbed and may reflect some radio disturbances or affect the TEC distribution in the ionosphere. 
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The earth's rotation is very slow compared with the the timescales of trapped radiation (microseconds for gyration, seconds for bounce between mirror points, minutes for drift around the earth) and the periods of precession and nutation are many thousands of years. What is important is the geomagnetic field which is not symmetric as the solar wind compresses it on the day side and extends it on the night side. This leads to diurnal variations as well as large, short-term variations from geomagnetic storms arising from features in the solar wind. On long timescales the earth's field is steadily changing in strength and direction and will reverse in the future. On the timescale of years we see a steady drift which alters the trapped radiation and must be allowed for in designing space systems and planning extravehicular activity on ISS. I agree that Hargreave's book is an excellent source.
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I have a coaxial cylinder with a cooper wire inside which is corona discharge happening. (1st picture)
Corona discharge is happening after ionization in this coaxial cylinder. My question is about calculating E (electric field)and Q (Amount of charge) in ionization area(2nd picture)! Would really appreciate if your help is included the process before ionization (E and Q).
Thanks in advance for your help!
2nd picture is taken from: IJPEST_Vol2_No2_03_pp082-088
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Hi Reza Rebk
In a uniform electric field, a gradual increase in voltage across a gap produces a breakdown of the gap in the form of a spark without any preliminary discharges. On the other hand, if the field is non-uniform, an increase in voltage will first cause a localised discharge in the gas to appear at points with the highest electric field intensity, namely at sharp points or where the electrodes are curved or on transmission line conductors. This form of discharge is called a corona discharge and can be observed as a bluish luminance.
When a gradually increasing voltage is applied across two conductors, initially nothing will be seen or heard. As the voltage is increased, the air surrounding the conductors get ionised, and at a certain voltage a hissing noise is heard caused by the formation of corona. This voltage is known as the disruptive critical voltage. A further increase in the voltage would cause a visible violet glow around the conductors. This voltage is the visual corona inception voltage.
The stress surrounding the conductor is a maximum at the conductor surface itself, and decreases rapidly as the distance from the conductor increases. Thus when the stress has been raised to critical value immediately surrounding the conductor, ionisation would commence only in this region and the air in this region would become conducting.
Under ordinary conditions, the breakdown strength of air can be taken as 30 kV/cm (E max = 30 kV/cm, so that RMS = 30/√2 = 21.2 kV/cm). Knowing that:
1. Corona will of course be affected by the physical state of the atmosphere,
2. When the surface of the conductor is irregular, it is more liable to corona,
3. When the surface of the conductor is irregular, it is more liable to corona.
The critical electric field can then be written as in the following equation:
Ec = 21.2*m1*m2[1 + 0.3/√(d*r)] kV/cm (Peek's xpression)
m1: factor depending of conductor surface,
m2: factor of weather conditions,
d : a correction factor ,
r : he conductor radius.
Good Luck,
Omar