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ABSTRACT: This paper describes a generally applicable technique for simultaneously measuring offset and gain of 64 analog fiber optic data links used for the DIII-D fixed Langmuir probes by embedding a reference voltage waveform in the optical transmitted signal before every tokamak shot. The calibrated data channels allow calibration of the power supply control fiber optic links as well. The array of fiber optic links and the embedded calibration system described here makes possible the use of superior modern data acquisition electronics in the control room.
The Review of scientific instruments 10/2012; 83(10):10D710. · 1.52 Impact Factor
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ABSTRACT: A new pair of in situ reciprocating Mach probes termed swing probes has been deployed on the DIII-D centerpost for the 2012 experimental campaign. When not deployed, the entire assembly is housed in a <5 cm space underneath the centerpost tiles. This design is unique in that the probe swings vertically through the edge plasma, taking measurements along a 180° arc with a 20 cm radius. The motion is powered by actuator coils that interact with the tokamak's magnetic field. Two electrodes maintain a Mach-pair orientation throughout the swing and provide measurements of saturation current, electron temperature, and parallel flow speeds up to the separatrix.
The Review of scientific instruments 10/2012; 83(10):10D723. · 1.52 Impact Factor
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ABSTRACT: The quality of plasma produced in a magnetic confinement fusion device is influenced to a large extent by the neutral gas surrounding the plasma. The plasma is fueled by the ionization of neutrals, and charge exchange interactions between edge neutrals and plasma ions are a sink of energy and momentum. Here we describe a diagnostic capable of measuring the spatial distribution of neutral gas in a magnetically confined fusion plasma. A high intensity (5 MW/cm(2)), narrow bandwidth (0.1 cm(-1)) laser is injected into a hydrogen plasma to excite the Lyman β transition via the simultaneous absorption of two 205 nm photons. The absorption rate, determined by measurement of subsequent Balmer α emission, is proportional to the number of particles with a given velocity. Calibration is performed in situ by filling the chamber to a known pressure of neutral krypton and exciting a transition close in wavelength to that used in hydrogen. We present details of the calibration procedure, including a technique for identifying saturation broadening, measurements of the neutral density profile in a hydrogen helicon plasma, and discuss the application of the diagnostic to plasmas in the DIII-D tokamak.
The Review of scientific instruments 10/2012; 83(10):10D701. · 1.52 Impact Factor
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J. Howard,
A. Diallo,
M. Creese,
S.L. Allen,
R.M. Ellis,
W. Meyer,
M.E. Fenstermacher,
G. D. Porter,
N. H. Brooks,
M. E. Van Zeeland, R. L. Boivin
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ABSTRACT: Various spatial heterodyne polarization interferometers for spectrally-resolved optical imaging of edge and core parameters in high temperature magnetized plasmas are described. Applications for such “coherence imaging” (CI) systems include imaging motional Stark effect and Zeeman effect polarimetry for determination of the magnetic field pitch angle, and passive and active (charge exchange recombination spectroscopy - CXRS) Doppler imaging of plasma temperature and flow. In this paper we describe spatial heterodyne coherence imaging systems and present first results of Doppler flow imaging in the DIII-D divertor.Instruments have been installed for imaging flows in the divertor and scrape-off-layer in the DIII-D tokamak and also for Doppler imaging on the H-1 heliac [1]. In the former case, single snapshot interferometric images of the plasma in CII 514nm, and CIII 465nm emission have been demodulated to obtain flow and ion temperature projections in both the scrape-off-layer and divertor. Flow field amplitudes in the divertor are found to be broad agreement with UEDGE modeling [2], and point the way towards experiments that address important divertor transport issues in future (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Beiträge aus der Plasmaphysik 03/2011; 51(2‐3):194 - 200.
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B. Tobias,
C. W. Domier,
T. Liang,
X. Kong,
L. Yu,
G. S. Yun,
H. K. Park,
I. G. J Classen,
J. E. Boom,
A. J. H. Donné,
T. Munsat,
R. Nazikian,
M. Van Zeeland, R. L. Boivin,
N. C. Luhmann
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ABSTRACT: A new electron cyclotron emission imaging diagnostic has been commissioned on the DIII-D tokamak. Dual detector arrays provide simultaneous two-dimensional images of Te fluctuations over radially distinct and reconfigurable regions, each with both vertical and radial zoom capability. A total of 320 (20 vertical×16 radial) channels are available. First data from this diagnostic demonstrate the acquisition of coherent electron temperature fluctuations as low as 0.1% with excellent clarity and spatial resolution. Details of the diagnostic features and capabilities are presented.
Review of Scientific Instruments 10/2010; 81(10):10D928-10D928-4. · 1.37 Impact Factor
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J Howard,
A Diallo,
M Creese,
B D Blackwell,
S L Allen,
R M Ellis,
G D Porter,
W Meyer,
M E Fenstermacher,
N H Brooks,
M E Van Zeeland, R L Boivin
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ABSTRACT: This article describes the results of spatial heterodyne Doppler "coherence imaging" of carbon ion flows in the divertor region of the DIII-D tokamak. Spatially encoded interferometric projections of doubly ionized carbon emission at 465 nm have been demodulated and tomographically inverted to obtain the spatial distribution of the carbon ion parallel flow and emissivity. The operating principles of the new instruments are described, and the link between measured properties and line integrals of the flow field are established. An iterative simultaneous arithmetic reconstruction procedure is applied to invert the interferometric phase shift projections, and the reconstructed parallel flow field amplitudes are found to be in reasonable agreement with UEDGE modeling.
The Review of scientific instruments 10/2010; 81(10):10E528. · 1.52 Impact Factor
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D L Rudakov,
J H Yu,
J A Boedo,
E M Hollmann,
S I Krasheninnikov,
R A Moyer,
S H Muller,
A Yu Pigarov,
M Rosenberg,
R D Smirnov, [......],
C P C Wong,
A L Roquemore,
C H Skinner,
W M Solomon,
S Ratynskaia,
M E Fenstermacher,
M Groth,
C J Lasnier,
A G McLean,
P C Stangeby
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ABSTRACT: Dust production and accumulation present potential safety and operational issues for the ITER. Dust diagnostics can be divided into two groups: diagnostics of dust on surfaces and diagnostics of dust in plasma. Diagnostics from both groups are employed in contemporary tokamaks; new diagnostics suitable for ITER are also being developed and tested. Dust accumulation in ITER is likely to occur in hidden areas, e.g., between tiles and under divertor baffles. A novel electrostatic dust detector for monitoring dust in these regions has been developed and tested at PPPL. In the DIII-D tokamak dust diagnostics include Mie scattering from Nd:YAG lasers, visible imaging, and spectroscopy. Laser scattering is able to resolve particles between 0.16 and 1.6 microm in diameter; using these data the total dust content in the edge plasmas and trends in the dust production rates within this size range have been established. Individual dust particles are observed by visible imaging using fast framing cameras, detecting dust particles of a few microns in diameter and larger. Dust velocities and trajectories can be determined in two-dimension with a single camera or three-dimension using multiple cameras, but determination of particle size is challenging. In order to calibrate diagnostics and benchmark dust dynamics modeling, precharacterized carbon dust has been injected into the lower divertor of DIII-D. Injected dust is seen by cameras, and spectroscopic diagnostics observe an increase in carbon line (CI, CII, C(2) dimer) and thermal continuum emissions from the injected dust. The latter observation can be used in the design of novel dust survey diagnostics.
The Review of scientific instruments 11/2008; 79(10):10F303. · 1.52 Impact Factor
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ABSTRACT: Two modular arrays of Langmuir probes designed to handle a heat flux of up to 25 MW/m(2) for 10 s exposures have been installed in the lower divertor target plates of the DIII-D tokamak. The 20 pyrolytic graphite probe tips have more than three times higher thermal conductivity and 16 times larger mass than the original DIII-D isotropic graphite probes. The probe tips have a fixed 12.5 degree surface angle to distribute the heat flux more uniformly than the previous 6 mm diameter domed collectors and a symmetric "rooftop" design to allow operation with reversed toroidal magnetic field. A large spring-loaded contact area improves heat conduction from each probe tip through a ceramic insulator into a cooled graphite divertor floor tile. The probe tips, brazed to molybdenum foil to ensure good electrical contact, are mounted in a ceramic tray for electrical isolation and reliable cable connections. The new probes are located 1.5 cm radially apart in a staggered arrangement near the entrance to the lower divertor pumping baffle and are linearly spaced 3 cm apart on the shelf above the in-vessel cryopump. Typical target plate profiles of J(sat), T(e), and V(f) with 4 mm spatial resolution are shown.
The Review of scientific instruments 11/2008; 79(10):10F125. · 1.52 Impact Factor
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ABSTRACT: A tangential viewing, 10.59 microm CO(2) laser polarimeter for electron density measurements based on plasma induced Faraday rotation has been installed on DIII-D. The system uses colinear right- and left-hand circularly polarized beams with a difference frequency of 40 MHz to generate the necessary signal for heterodyne phase detection. The high-resolution phase information required to adequately resolve degree level polarization rotation is obtained using an all-digital "real-time" phase demodulation scheme based on modern digital signal processing techniques. Initial application of the system to DIII-D disruption mitigation experiments utilizing "massive gas jet" injection exhibits reliable operation and excellent agreement with CO(2) interferometer measurements; interestingly, the obtained Faraday rotation angles are in the range of those expected in ITER plasmas.
The Review of scientific instruments 11/2008; 79(10):10E719. · 1.52 Impact Factor
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A. Litnovsky,
D.L. Rudakov,
G. De Temmerman,
P. Wienhold,
V. Philipps,
U. Samm,
A.G. McLean,
W.P. West,
C.P.C. Wong,
N.H. Brooks, [......],
M.E. Fenstermacher,
M. Groth,
C.J. Lasnier, R.L. Boivin,
A.W. Leonard,
A. Romanyuk,
T. Hirai,
G. Pintsuk,
U. Breuer,
A. Scholl
Fusion Engineering and Design 01/2008; 83(1):79-89. · 1.49 Impact Factor
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ABSTRACT: Langmuir probes are commonly used plasma diagnostics measuring localized floating potential, electron temperature, particle flux, and electron density. A major upgrade of DIII-D's lower divertor required an improved design of Langmuir probe arrays to accommodate the higher heat fluxes incident on the new divertor plasma facing components. It was also advantageous to decrease the linear spacing between electrodes and to improve the ease of maintenance. The new electrode design distributes the heat flux almost uniformly over its surface because of the fixed angle roof-top shape. The advanced design features 16 x increased thermal mass half the peak heat flux. Thermal coupling of the probe to the surrounding tile was greatly enhanced by increasing the thermal contact area. A novel probe mounting system has the entire probe array supported in a single tray. After an annual operational period, the probes yielded reliable data and showed little or no erosion.
Fusion Engineering, 2007. SOFE 2007. 2007 IEEE 22nd Symposium on; 07/2007
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D L Rudakov,
W Jacob,
K Krieger,
A Litnovsky,
V Philipps,
W P West,
C P C Wong,
S L Allen,
R J Bastasz,
J A Boedo, [......],
M Groth,
E M Hollmann,
C J Lasnier,
A G McLean,
R A Moyer,
P C Stangeby,
W R Wampler,
J G Watkins,
P Wienhold,
J Whaley
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ABSTRACT: A strong effect of a moderately elevated surface temperature on net carbon deposition and deuterium co-deposition in the DIII-D divertor was observed under detached conditions. A graphite DiMES sample with a 2 mm wide, 18 mm deep gap lined with silicon catcher plates was exposed to lower-single-null (LSN) L-mode plasmas first at room temperature, and then pre-heated to 200 °C by a built-in electrical heater. At the elevated temperature, deuterium co-deposition in the gap was reduced by an order of magnitude. At the plasma-facing surface of the pre-heated sample net carbon erosion was measured at a rate of 3 nm s−1, whereas without pre-heating net deposition is normally observed under detachment. In a related experiment three sets of molybdenum mirrors recessed 2 cm below the divertor floor were exposed to identical LSN ELMy H-mode discharges. The first set of mirrors exposed at ambient temperature exhibited net carbon deposition at a rate of up to 3.7 nm s−1 and suffered a significant drop in reflectivity. In contrast, two other mirror sets exposed at elevated temperatures between 90 and 175 °C exhibited practically no carbon deposition and their optical reflectivity in the wavelength range above 500 nm was essentially preserved.
Physica Scripta 03/2007; 2007(T128):29. · 1.20 Impact Factor
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ABSTRACT: A fiber optic, heterodyne, two-color interferometer utilizing wavelength division multiplexing technology has been developed for measuring electron density in plasmas. Vibration compensation is accomplished via common path 1.31 and 1.55 μ m distributed feedback laser interferometers. All beam combining, splitting, frequency modulation, and collimation are accomplished by shared single-mode fiber optic components. Measurements of an argon radio-frequency generated plasma with electron densities of 10<sup>20</sup> m <sup>-3</sup> show effective vibration compensation and typical line-density resolution of approximately 2×10<sup>19</sup> m <sup>-2</sup> .
Review of Scientific Instruments 11/2006; · 1.37 Impact Factor
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ABSTRACT: The spatial structure of toroidal Alfvén eigenmodes and reversed shear Alfvén eigenmodes in DIII-D is obtained from electron-cyclotron-emission measurements. Peak measured temperature perturbations are of similar magnitude for both toroidal Alfvén eigenmodes and reversed shear Alfvén eigenmodes and found to be deltaT(e)/T(e) approximately equal to 0.5%. Simultaneous measurements of density fluctuations using beam-emission spectroscopy indicate deltan(e)/n(e) approximately equal to 0.25%. Predictions of the measured temperature and density perturbation profiles as well as deltaT(e)/deltan(e) from the ideal magnetohydrodynamic code NOVA are in close agreement with experiment.
Physical Review Letters 10/2006; 97(13):135001. · 7.37 Impact Factor
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ABSTRACT: We present various aspects of the calibration of the TFTR lost alpha diagnostic. The diagnostic consists of four detectors, forming a poloidal array at the bottom of TFTR inside the vacuum vessel. The detector is composed of a ZnS(Ag) scintillator and a pair of collimating apertures which permit pitch angle, energy, and time resolution of the escaping flux of high‐energy ions (MeV range). The first goal of this study was to establish the absolute calibration of the diagnostic for different particle types and energies. This enables us to compare for the first time, measured losses with loss calculations based on a first‐orbit model. However, the factor of 2 uncertainty in the final calibration is still too large for full, quantitative comparisons of the data with the theory based on absolute flux measurements alone. We also present some of the aspects related to the detector’s resolution capabilities, its temperature dependence, and its time response.
Review of Scientific Instruments 11/1992; · 1.37 Impact Factor
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R. K. Fisher,
D. C. Pace,
M García-Muñoz, R L Boivin,
E. D. Frederickson,
W. W. Heidbrink,
C. M. Muscatello,
R. Nazikian,
C. C. Petty,
M A Van Zeeland,
Y. B. Zhu
McKenna, C.: 37th European Physical Society Conference on Plasma Physics. Contributed Papers, European Physical Society (2010).
