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Title: Gas Jet Disruption Mitigation Studies on Alcator C-Mod and DIII-D

Authors:
 [1];  [2];  [3];  [4];  [5];  [4];  [3];  [6];  [5];  [7];  [4];  [8];  [5];  [9];  [7];  [9];  [5];  [7];  [1];  [5] more »;  [7];  [1];  [7];  [7];  [10];  [5] « less
  1. Plasma Sciences and Fusion Center, Massachusetts Institute of Technology (MIT)
  2. University of California
  3. University of Wisconsin, Madison
  4. Massachusetts Institute of Technology (MIT)
  5. University of California, San Diego
  6. ORNL
  7. General Atomics, San Diego
  8. Oak Ridge National Laboratory (ORNL)
  9. Lawrence Livermore National Laboratory (LLNL)
  10. Los Alamos National Laboratory (LANL)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1118765
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Fusion; Journal Volume: 47; Journal Issue: 9
Country of Publication:
United States
Language:
English

Citation Formats

Granetz, R. S., Hollmann, E.M., Whyte, D. G., Izzo, V. A., Antar, G. Y., Badar, A., Bakhtiari, M., Biewer, Theodore M, Boedo, J., Evans, T. E., Hutchinson, I., Jernigan, T. C., Gray, D. S., Groth, M., Humphreys, D. A., Lasnier, C. J., Moyer, R. A., Parks, P. B., Reinke, M. L., Rudakov, D. L., Strait, E. J., Terry, J. L., Wesley, J., West, W. P., Wurden, G., and Yu, J.. Gas Jet Disruption Mitigation Studies on Alcator C-Mod and DIII-D. United States: N. p., 2007. Web. doi:10.1088/0029-5515/47/9/003.
Granetz, R. S., Hollmann, E.M., Whyte, D. G., Izzo, V. A., Antar, G. Y., Badar, A., Bakhtiari, M., Biewer, Theodore M, Boedo, J., Evans, T. E., Hutchinson, I., Jernigan, T. C., Gray, D. S., Groth, M., Humphreys, D. A., Lasnier, C. J., Moyer, R. A., Parks, P. B., Reinke, M. L., Rudakov, D. L., Strait, E. J., Terry, J. L., Wesley, J., West, W. P., Wurden, G., & Yu, J.. Gas Jet Disruption Mitigation Studies on Alcator C-Mod and DIII-D. United States. doi:10.1088/0029-5515/47/9/003.
Granetz, R. S., Hollmann, E.M., Whyte, D. G., Izzo, V. A., Antar, G. Y., Badar, A., Bakhtiari, M., Biewer, Theodore M, Boedo, J., Evans, T. E., Hutchinson, I., Jernigan, T. C., Gray, D. S., Groth, M., Humphreys, D. A., Lasnier, C. J., Moyer, R. A., Parks, P. B., Reinke, M. L., Rudakov, D. L., Strait, E. J., Terry, J. L., Wesley, J., West, W. P., Wurden, G., and Yu, J.. Mon . "Gas Jet Disruption Mitigation Studies on Alcator C-Mod and DIII-D". United States. doi:10.1088/0029-5515/47/9/003.
@article{osti_1118765,
title = {Gas Jet Disruption Mitigation Studies on Alcator C-Mod and DIII-D},
author = {Granetz, R. S. and Hollmann, E.M. and Whyte, D. G. and Izzo, V. A. and Antar, G. Y. and Badar, A. and Bakhtiari, M. and Biewer, Theodore M and Boedo, J. and Evans, T. E. and Hutchinson, I. and Jernigan, T. C. and Gray, D. S. and Groth, M. and Humphreys, D. A. and Lasnier, C. J. and Moyer, R. A. and Parks, P. B. and Reinke, M. L. and Rudakov, D. L. and Strait, E. J. and Terry, J. L. and Wesley, J. and West, W. P. and Wurden, G. and Yu, J.},
abstractNote = {},
doi = {10.1088/0029-5515/47/9/003},
journal = {Nuclear Fusion},
number = 9,
volume = 47,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Measurements of the radiation dynamics during an Alcator C-Mod disruption induced by a high pressure He/Ar gas jet are presented. Data are analysed from four 22-channel Absolute eXtreme UltraViolet diode arrays viewing on horizontal planes from different toroidal and vertical locations, both towards and away from the gas jet. Prior to the loss of the core plasma stored energy, strong emission is seen from a shell at the plasma edge that expands toroidally and poloidally away from the the gas jet at 650 m s -1, consistent with neutral expansion rates. Both the energy loss from this region and frommore » the bulk plasma are shown to be of comparable magnitudes and important in dissipating the electron thermal energy outside the q = 2 surface. During the thermal quench, line-integrated brightnesses exceed 100 MW m -2. But while the brightness ratio of equivalent toroidally/vertically spaced views varies from 0.4 to 4.0, energy loss integrated over the disruption is shown to be symmetric to within 25%. Radiative energy loss local to the gas jet is shown to preheat nearby surfaces making them more susceptible to melting when the bulk of the thermal energy is lost.« less
  • Disruption mitigation experiments using massive gas injection (MGI) on Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] and DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] have shown that magnetohydrodynamics (MHD) plays an important role. The three-dimensional MHD code NIMROD [Sovinec et al., J. Comput. Phys. 195, 355 (2004)] has been extended to include atomic physics taken from the KPRAD code to perform simulations of MGI. Considerable benchmarking of the code has been done against Alcator C-Mod for neon and helium gas jet experiments. The code successfully captures the qualitative sequence of events observed in MGI experimentsmore » up to the end of the thermal quench. Neon jet simulations also show quantitative agreement with the experimental thermal quench onset time. For helium gas jets, we show that a small percent boron density can significantly alter the results even in the presence of a helium jet with three orders of magnitude higher density. The thermal quench onset time is considerably overpredicted unless boron radiation is included. A DIII-D helium jet simulation shows a faster rise time for total radiated power than the experiment, but comparable amplitude. Similar to the important role of boron in C-Mod, carbon radiation is a significant factor in DIII-D helium jet simulations and experiments.« less
  • Injection of massive quantities of gas is a promising technique for fast shutdown of ITER for the purpose of avoiding divertor and first wall damage from disruptions. Previous experiments using massive gas injection (MGI) to terminate discharges in the DIII-D tokamak have demonstrated rapid shutdown with reduced wall heating and halo currents (relative to natural disruptions) and with very small runaway electron (RE) generation [1]. Figure 1 shows time traces which give an overview of shutdown time scales. Typically, of order 5 x 10{sup 22} Ar neutrals are fired over a pulse of 25 ms duration into stationary (non-disrupting) discharges.more » The observed results are consistent with the following scenario: within several ms of the jet trigger, sufficient Ar neutrals are delivered to the plasma to cause the edge temperature to collapse, initiating the inward propagation of a cold front. The exit flow of the jet [Fig. 1(a)] has a {approx} 9 ms rise time; so the quantity of neutrals which initiates the edge collapse is small (<10{sup 20}). When the cold front reaches q {approx} 2 surface, global magnetohydrodynamic (MHD) modes are destabilized [2], mixing hot core plasma with edge impurities. Here, q is the safety factor. Most (>90%) of the plasma thermal energy is lost via impurity radiation during this thermal quench (TQ) phase. Conducted heat loads to the wall are low because of the cold edge temperature. After the TQ, the plasma is very cold (of order several eV), so conducted wall (halo) currents are low, even if the current channel contacts the wall. The plasma current profile broadens and begins decaying resistively. The decaying current generates a toroidal electric field which can accelerate REs; however, RE beam formation appears to be limited in MGI shutdowns. Presently, it is thought that the conducted heat flux and halo current mitigation qualities of the MGI shutdown technique will scale well to a reactor-sized tokamak. However, because of the larger RE gain from avalanching and the presence of a RE seed population due to Compton-scattered fast electrons, it is possible that a RE beam can be formed well into the CQ, after the flux surfaces initially destroyed by the TQ MHD have had time to heal. Crucial MGI issues to be studied in present devices are therefore the formation, amplification, and transport of RE and the transport of impurities into the core plasma (important because the presence of impurities can, via collisional drag, help suppress RE amplification). In the study of impurity transport, both neutral delivery (directly driven into the core by the jet pressure) and ion delivery (mixed into the core by MHD) are of interest, as both contribute to RE drag.« less
  • Local measurements of line emission of either intrinsic or gas puffed impurities will be performed around and below the X point. Such spectroscopic measurements, together with divertor Thomson scattering and bolometric imaging will enable estimates of divertor impurity particle distributions and power losses. A proposed multilayer mirror (MLM) diagnostic mounted inside the tokamak vessel will measure XUV (100{endash}200 {Angstrom}) emission from impurities at multiple locations in the divertor region of the C-Mod tokamak. A prototype of this instrument measuring NV at 162.6 {Angstrom} is scheduled to be installed on C-Mod with a single chordal view of the X point. Amore » multichordal/multispectral device using MLMs and gratings has been designed for the DIII-D tokamak. The instrument will measure the resonance emission of CII to CVI from 40{endash}2000 {Angstrom}, thus enabling a more direct and reliable estimate of the impurity content in the divertor. At DIII-D, the device will be mounted on a port below the mid plane avoiding spectroscopic contamination from the core plasma. {copyright} {ital 1997 American Institute of Physics.}« less