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ABSTRACT: One of the most important and intriguing processes in space and laboratory plasmas is magnetic field line reconnection: it provides a mechanism to rapidly convert magnetic field energy into particle energy. For example, magnetic reconnection is considered to be a key factor in the onset and evolution of solar flares and magnetic storms. These two phenomena play a critical role in the dynamics of the near-Earth space environment, and are an integral part of "space weather" that can adversely impact communication and navigation systems.
11/2012;
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V L Kantsyrev,
A A Esaulov,
A S Safronova,
A L Velikovich, L I Rudakov,
G C Osborne,
I Shrestha,
M E Weller,
K M Williamson,
A Stafford,
V V Shlyaptseva
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ABSTRACT: The influence of an induced axial magnetic field on plasma dynamics and radiative characteristics of Z pinches is investigated. An axial magnetic field was induced in a novel Z-pinch load: a double planar wire array with skewed wires (DPWAsk), which represents a planar wire array in an open magnetic configuration. The induced axial magnetic field suppressed magneto-Rayleigh-Taylor (MRT) instabilities (with m = 0 and m = 1 instability modes) in the Z-pinch plasma. The influence of the initial axial magnetic field on the structure of the plasma column at stagnation was manifested through the formation of a more uniform plasma column compared to a standard double planar wire array (DPWA) load [V. L. Kantsyrev et al., Phys. Plasmas 15, 030704 (2008)]. The DPWAsk load is characterized by suppression of MRT instabilities and by the formation of the sub-keV radiation pulse that occurs before the main x-ray peak. Gradients in plasma parameters along the cathode-anode gap were observed and analyzed for DPWAsk loads made from low atomic number Z (Al) and mid-Z (brass) wires.
Physical Review E 10/2011; 84(4 Pt 2):046408. · 2.26 Impact Factor
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V L Kantsyrev,
A S Safronova,
A A Esaulov,
K M Williamson,
I Shrestha,
G C Osborne,
M E Weller,
M F Yilmaz,
N D Ouart,
V V Shlyaptseva,
A L Velikovich, L I Rudakov
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ABSTRACT: The shaping of the x-ray radiation pulse is very important in both radiation physics research and Inertial Confinement Fusion studies. The novel planar wire array (PWA) was found to be the effective radiator tested at the university-scale 1.6 MA, 100 ns Zebra generator. The single PWA consists of a single row of wires that are parallel to each other, while the double planar wire array (DPWA) and triple planar wire array (TPWA) include two or three parallel plane wire rows, respectively. All multi-planar geometries resulted in a cascade-type array implosion with a complicated multi-step precursor formation before plasma stagnation. The PWAs (without additional core foam target) feature a dynamic precursor evolution that is a powerful tool for x-ray pulse shaping. The shape and timing of the x-ray pulse from different PWAs were theoretically predicted and experimentally analyzed for a variety of planar wire arrays.
Journal of Physics Conference Series 09/2010; 244(3):032030.
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B Jones,
D J Ampleford,
R A Vesey,
M E Cuneo,
C A Coverdale,
E M Waisman,
M C Jones,
W E Fowler,
W A Stygar,
J D Serrano,
M P Vigil,
A A Esaulov,
V L Kantsyrev,
A S Safronova,
K M Williamson,
A S Chuvatin, L I Rudakov
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ABSTRACT: An indirect drive configuration is proposed wherein multiple compact Z-pinch x-ray sources surround a secondary hohlraum. Planar compact wire arrays allow reduced primary hohlraum surface area compared to cylindrical loads. Implosions of planar arrays are studied at up to 15 TW x-ray power on Saturn with radiated yields exceeding the calculated kinetic energy, suggesting other heating paths. X-ray power and yield scaling studied from 1-6 MA motivates viewfactor modeling of four 6-MA planar arrays producing 90 eV radiation temperature in a secondary hohlraum.
Physical Review Letters 03/2010; 104(12):125001. · 7.37 Impact Factor
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A. S. Chuvatin,
V. L. Kantsyrev, L. I. Rudakov,
M. E. Cuneo,
A. L. Astanovitskiy,
R. Presura,
A. S. Safronova,
A. A. Esaulov,
W. Cline,
K. M. Williamson,
I. Shrestha,
M. F. Yilmaz,
G. C. Osborne,
M. Weller,
T. Jarrett,
B. LeGalloudec,
V. Nalajala,
T. D. Pointon,
K. A. Mikkelson
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ABSTRACT: The Load Current Multiplier concept (LCM) was validated for the first time on a high‐voltage nanosecond pulse‐power generator. The designed new device allowed to increase the load current from the nominal 0.8–0.9 MA up to 1.6 MA in static loads with constant inductance and up to 1.4 MA in a planar wire‐array plasma loads. These results were achieved without modifying the generator energetic or architecture. LCM allowed both the load magnetic energy increase and the increase of soft X‐ray radiation from z‐pinch plasmas.
AIP Conference Proceedings. 01/2009; 1088(1):253-258.
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Edmund P. Yu,
M. E. Cuneo,
M. P. Desjarlais,
R. W. Lemke,
D. B. Sinars,
T. A. Haill,
E. M. Waisman,
G. R. Bennett,
C. A. Jennings,
T. A. Mehlhorn,
T. A. Brunner,
H. L. Hanshaw,
J. L. Porter,
W. A. Stygar, L. I. Rudakov
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ABSTRACT: The implosion phase of a wire-array Z pinch is investigated using three-dimensional (3D) simulations, which model the mass ablation phase and its associated axial instability using a mass injection boundary condition. The physical mechanisms driving the trailing mass network are explored, and it is found that in 3D the current paths though the trailing mass can reduce bubble growth on the imploding plasma sheath, relative to the 2D (r,z) equivalent. Comparison between the simulations and a high quality set of experimental radiographs is presented.
Physics of Plasmas 02/2008; 15(5):056301-056301-9. · 2.15 Impact Factor
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A. L. Velikovich,
R. W. Clark,
J. Davis,
Y. K. Chong,
C. Deeney,
C. A. Coverdale,
C. L. Ruiz,
G. W. Cooper,
A. J. Nelson,
J. Franklin, L. I. Rudakov
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ABSTRACT: A deuterium gas-puff load imploded by a multi-MA current driver from a large initial diameter could be a powerful source of fusion neutrons, a plasma neutron source (PNS). Unlike the beam-target neutrons produced in Z-pinch plasmas in the 1950s and deuterium-fiber experiments in the 1980s, the neutrons generated in deuterium gas-puffs with current levels achieved in recent experiments on the Z facility at Sandia National Laboratories could contain a substantial fraction of thermonuclear origin. For recent deuterium gas-puff shots on Z, our analytic estimates and one- and two-dimensional simulations predict thermal neutron yields ∼ 3×1013, in fair agreement with the yields recently measured on Z [
C. A. Coverdale et al., Phys. Plasmas (to be published)
]. It is demonstrated that the hypothesis of a beam-target origin of the observed fusion neutrons implies a very high Z-pinch-driver-to-fast-ions energy transfer efficiency, 5 to 10%, which would make a multi-MA deuterium Z-pinch the most efficient light-ion accelerator. No matter what mechanism is eventually determined to be responsible for generating fusion neutrons in deuterium gas-puff shots on Z, the deuterium neutron yield is shown to scale as Yn ∼ Im4, where Im is the peak current of the pinch. Theoretical estimates and numerical modeling of deuterium gas-puff implosions demonstrate that the yields of thermonuclear fusion neutrons that can be produced on ZR and the next-generation machines are sufficiently high to make PNS the most powerful, cost- and energy-efficient laboratory sources of 2.5−14 MeV fusion neutrons, just like plasma radiation sources are the most powerful sources of soft and keV x rays. In particular, the predicted deuterium-tritium thermal neutron-producing capability of PNS driven by the next-generation ZR and ZX accelerators is ∼ 5×1016 and ∼ 1018, respectively.
Physics of Plasmas 02/2007; 14(2):022701-022701-16. · 2.15 Impact Factor
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V.L. Kantsyrev, L.I. Rudakov,
A.S. Safronova,
D.A. Fedin,
V.V. Ivanov,
A.L. Velikovich,
A.A. Esaulov,
A.S. Chuvatin,
K. Williamson,
N.D. Ouart,
V. Nalajala,
G. Osborne,
I. Shrestha,
M.F. Yilmaz,
S. Pokala,
P. Laca,
T.E. Cowan
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ABSTRACT: The radiative performance of Al, Ni, and W planar wire arrays, to which little energy could be coupled via the conventional magnetic-to-kinetic conversion mechanism, is investigated. However, the planar wire arrays were shown to radiate much more energy in a short intense peak than possible due to dissipation of the kinetic energy. The planar array gives the unique possibility of seeing the evolution of the small-scale inhomogeneity of wire-array plasmas during wire ablation and implosion phases and highlights the importance of the Hall plasma phenomena and their impact on the dynamics, energy coupling, and radiation performance of wire-array Z-pinches
IEEE Transactions on Plasma Science 11/2006; · 1.17 Impact Factor
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ABSTRACT: The dynamics of inhomogeneous, reversed field current layers in the Hall limit (i.e., characteristic length scales the ion inertial length) are briefly reviewed. We demonstate that a density inhomogeneity along the current direction can dramatically redistribute the magnetic field and plasma via magnetic shock-like or rarefaction waves. The relative direction between the density gradient and current flow plays a critical role in the evolution of the current sheet. Specifically a current sheet can become very thin rapidly when the density gradient is directed opposite to the current. We also show that magnetic reconnection proceeds asymmetrically in a three dimensional system. A localized magnetic field perturbation induces a wave structure that propagates in the direction of the electron drift (i.e., opposite to the current). The propagating wave structure is a Hall phenomenon associated with magnetic field curvature. The interaction between the propagating wave structure and an evolving current layer can lead to rapid magnetic field line reconnection. We apply our results to laboratory and space plasma processes.
Physica Scripta 07/2006; 2004(T107):20. · 1.20 Impact Factor
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V.L. Kantsyrev,
A.S. Safronova,
D.A. Fedin,
V.V. Ivanov,
A.A. Esaulov,
V. Nalajala,
I. Shrestha,
S. Pokala,
K. Williamson,
N.D. Ouart,
M.F. Yilmaz,
P. Laca,
T.E. Cowan, L.I. Rudakov,
B. Jones,
C.A. Coverdale,
C. Deeney,
P.D. LePell,
A.L. Velikovich,
A.S. Chuvatin
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ABSTRACT: In the following experiments, we studied implosions of different wire arrays and X-pinches produced on the 1-MA Zebra generator at the University of Nevada, Reno. Diagnostics included both spatially-resolved and time-gated X-ray imaging and spectroscopy, and laser probing. In particular, we compared planar wire arrays, to which little energy could be coupled via the conventional magnetic-to-kinetic conversion mechanism, to cylindrical wire arrays of comparable dimensions and mass. The planar wire arrays were shown to radiate much higher peak power and more energy in subkiloelectronvolt and kiloelectronvolt spectral ranges than cylindrical wire arrays. We tested the theoretical conjecture that enhanced resistivity due to the small-scale inhomogeneity of wire-array plasmas has a major effect on dynamics, energy coupling and radiation performance of wire-array Z-pinches. The study of Al, Alumel, and W cylindrical wire arrays shows a wide variety of characteristic behaviors in plasma implosions discussed hereinafter. Additional experimental results for symmetric and asymmetric, uniform stainless steel, Cu, Mo, combined Al/Mo, Mo/Al, Al/W, W/Al, and Mo/W X-pinches are also presented. New data for the total radiation yield are obtained. The planar structures of X-pinch plasma and the corresponding electron beam was observed for most of X-pinches. The generation of hot spots along original wires positions-cooler than those from the cross-wire region-and arc structures with hot spots between wires were found for X-pinches composed from Al, Cu, and W wires.
IEEE Transactions on Plasma Science 05/2006; · 1.17 Impact Factor
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ABSTRACT: Summary form only given. We investigate the three-dimensional dynamics of X- and Z-pinches using the NRL 3D Hall MHD code VooDoo. The goal is to determine the final magnetic field structure for different initial perturbations or non-equilibrium states in both the ideal MHD and the Hall MHD limit. The VooDoo code has successfully studied the nonlinear Hall dynamics of the current layer and magnetic reconnection in both 2D and 3D simulation studies. In the current study we conclude that there is tendency for establishing a force free helical magnetic field topology in many cases. Influence of resistivity on the process of force free configuration formation will be also analyzed by 3D hybrid code Dolphin used at UNR. We will compare our results with several experimental results
Plasma Science, 2005. ICOPS '05. IEEE Conference Record - Abstracts. IEEE International Conference on; 07/2005
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IEEE Transactions on Plasma Science 07/2005; · 1.17 Impact Factor
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ABSTRACT: We discuss a new opportunity of using Z-pinch plasma radiation sources for generating Ar K-shell radiation and harder keV quanta. Our approach to keV X-ray generation is based upon an analogy with laser fusion, where the imploding shell compressionally heats the low-density inner mass. The suggested design of a Z-pinch load consists then of one or two heavy outer shell(s) with a lower mass on-axis fill (i.e., central gas jet) producing most of the radiation. The outer shell is not supposed to radiate and thus does not need to have high specific energy characterized by the large η parameter (Whitney et al., 1990). Thus, the heavy outer shell does not need to have a very large initial diameter for its implosion to be matched to the long-pulse current driver. Rather, we want to have a large amount of energy from the driver coupled to this shell by the moment when the shell collides with the low-density fill and eventually converts much of this energy to the thermal energy of the on-axis plasma. This configuration is investigated numerically in the framework of a one-dimensional radiation-magneto-hydrodynamics model for the case of Ar K-shell radiators. It is demonstrated that the Ar fill is heated in two stages. The first stage corresponds to the shock heating and thermal conduction in an initially low-density fill, and it allows preheating the fill while avoiding significant losses in soft radiation. The fill radiator is then compressed quasi-adiabatically and is heated-up to the temperature optimum for K-shell quanta generation. Diffusion of the driving magnetic field is shown to always suppress the conductive heat losses from the hot on-axis plasma to the cold outer shell. Absorption of the K-lines emitted near the axis in the surrounding plasma could be avoided by filling the outer shell with a different gas (like N-on-Ar), which allows a substantial increase in the observed keV X-ray radiation yields.
IEEE Transactions on Plasma Science 05/2005; · 1.17 Impact Factor
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ABSTRACT: Two-dimensional Hall magnetohydrodynamic simulations are used to determine the magnetic reconnection rate in the Hall limit. The simulations are run until a steady state is achieved for four initial current sheet thicknesses: L=1,5,10, and 20c/omega(pi), where c/omega(pi) is the ion inertial length. It is found that the asymptotic (i.e., time independent) state of the system is nearly independent of the initial current sheet width. Specifically, the Hall reconnection rate is weakly dependent on the initial current layer width and is partial differential Phi/ partial differential t less, similar 0.1V(A0)B0, where Phi the reconnected flux, and V(A0) and B0 are the Alfvén velocity and magnetic field strength in the upstream region. Moreover, this rate appears to be independent of the scale length on which the electron "frozen-in" condition is broken (as long as it is <c/omega(pi)) and of the system size.
Physical Review Letters 10/2004; 93(17):175003. · 7.37 Impact Factor
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ABSTRACT: Summary form only given. We discuss new opportunities of using long-implosion Z-pinch plasma radiation sources for generating Ar K-shell radiation and harder keV quanta. Until recently it was believed that multi-MA current pulses with 300 to 1000 ns rise time cannot be used for K-shell radiation production because the initial load diameter needed for matching the implosion to the generator must be very large, and the pinch plasma would be distorted by Rayleigh-Taylor instability too much to become an efficient radiator at stagnation. Recent experiments demonstrated that this does not have to be the case: implosions of structured gas-puff loads (shell-on-shell, or shell-on-shell-on gas fill) can produce high quality, tight pinches at stagnation, generating reasonable amounts of keV X-rays. In view of these new developments, the conventional limitations on the PRS performance should be reconsidered. We discuss an approach to keV X-ray generation based upon an analogy with laser fusion, where the imploding shell compressionally heats the low-density inner mass. Our design of a Z-pinch load suitable for producing outer shell(s) with low-density on-axis mass (i.e., central gas jet) producing most of the radiation. The heavy outer shell does not need to have a very large initia diameter for its implosion to be matched to the long-pulse current driver. This is because the outer shell is not supposed to radiate, and therefore does not need to have high specific energy characterized by the large eta parameter. Rather, we want to couple a large amount of energy form the driver to this heavy shell to make it slowly implode and eventually convert much of this energy to the thermal energy of the low-density on-axis plasma. 1D RMHD simulations for double-shell-Ar-on-Kr-jet demonstrate that the kinetic energy coupled to the outer shell could be efficiently converted into the thermal energy of the on-axis plasma via compressional heating and thermal conduction, achieving sufficiently high values of the effective eta parameter in this plasma rapidly enough to produce K-shell emission and to mitigate the soft X-ray energy losses.
Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts. The 31st IEEE International Conference on; 08/2004
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ABSTRACT: We demonstrate the existence of a stationary rarefaction wave in a current-carrying plasma. The result unexpectedly mismatches with the commonly accepted viewpoint about the impossibility of rarefaction shocks in gases or plasmas. The discovered wave may appear when the magnetic field has penetrated into the plasma and magnetized the electrons. At this stage, the wave front is formed at the cathode and propagates towards the anode through the magnetized quasineutral plasma. The case of low collisionality is investigated analytically. This phenomenon could explain the recent surprising experimental observations of a local plasma density drop in several laboratory plasmas.
Physical Review Letters 04/2004; 92(9):095007. · 7.37 Impact Factor
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ABSTRACT: New analytical and numerical results of the dynamics of inhomogeneous, reversed field current layers in the Hall limit (i.e., characteristic length scales ≲ the ion inertial length) are presented. Specifically, the two- and three-dimensional evolution of a current layer that supports a reversed field plasma configuration and has a density gradient along the current direction is studied. The two-dimensional study demonstrates that a density inhomogeneity along the current direction can dramatically redistribute the magnetic field and plasma via magnetic shock-like or rarefaction waves. The relative direction between the density gradient and current flow plays a critical role in the evolution of the current sheet. One important result is that the current sheet can become very thin rapidly when the density gradient is directed opposite to the current. The three-dimensional study uses the same plasma and field configuration as the two-dimensional study but is also initialized with a magnetic field perturbation localized along the current channel upstream of the plasma inhomogeneity. The perturbation induces a magnetic wave structure that propagates in the direction of the electron drift (i.e., opposite to the current). The propagating wave structure is a Hall phenomenon associated with magnetic field curvature. The interaction between the propagating wave structure and the evolving current layer can lead to rapid magnetic field line reconnection. The results are applied to laboratory and space plasma processes. © 2003 American Institute of Physics.
Physics of Plasmas 07/2003; 10(8):3139-3150. · 2.15 Impact Factor
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ABSTRACT: This paper was written for the Culham conference two years ago, but owing to circumstances beyond the control of the authors it has not been widely circulated. The paper is, in the main, the presentation of an original method for considering a weakly turbulent plasma. The virtue of this method, as compared with the normal methods which are based on perturbation theory, lies in its simplicity and physical clarity. It was first shown, using just this very method, that a weakly turbulent plasma can exhibit new types of oscillation and instability and that the propagation law for electromagnetic waves is substantially altered. There has now begun a wide experimental study of plasma turbulence. The method presented here for theoretically discussing turbulence enables new results to be easily obtained. It is relatively simple to understand and can be grasped by non-theoreticians. The authors therefore consider that the publication of this article serves a useful purpose.
Plasma Physics 12/2002; 9(6):719.
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ABSTRACT: It has been observed over the years that the energy coupled to the load
in many z-pinch experiments is larger than can be accounted for by the
sum of the jxB work and classical Ohmic heating. Moreover, this energy
enhancement appears to be a function of the generator design, increasing
as the risetime of the current is increased. In recent experiments on
the Saturn generator, for example, which was operated at current
risetimes in excess of 160 ns, observed energy enhancements were factors
of 2 to 4 times the energy input expected from JxB work alone. When
Saturn operates with risetimes of less than 90 ns, much smaller energy
enhancements over the JxB energy are seen. In the past, it was
conjectured that some form of anomalous resistivity was needed to
account for the extra energy input, while recently, a new idea was
proposed based on the buildup of internally generated tubes of magnetic
flux energy.[1,2] It was hypothesized that the growth of the
Rayleigh-Taylor instability at the surface of the z-pinch plasma would
generate bubbles of magnetic flux-tube energy that deposit their energy
in the plasma at a current-to-the-third-power rate. While 0-D modeling
of the Saturn experiments shows that an anomalously high load resistance
can input the required energy needed to match the x-ray data, an
alternate mechanism than magnetic flux-tubes exists for anomalous
heating that is based on the production of micro-instabilities at the
pinch surface. Both this and the flux-tube model are phenomenological
and require guidance from experiments to be implemented. Several issues
that arise from these enhanced energy coupling mechanisms are discussed
in this paper.
11/2002; 651:358-363.
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ABSTRACT: We present new analytical and numerical results of the dynamics of reversed field current layers in the Hall limit (i.e., characteristic length scales smaller than the ion inertial length). A rapid, localized thinning of the current layer leads to the generation of a nonlinear, shocklike structure that propagates in the B x inverted Delta(n) direction. This magnetic structure is self-supportive and can lead to a nonlocal thinning of the current layer and the release of magnetic energy.
Physical Review Letters 09/2002; 89(9):095002. · 7.37 Impact Factor
