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64. Characteristics of low-q disruptions in PBX

Author

Kaye, SM, Jahns, GL, Morris, AW, Sesnic, S, Bol, K, Chance, MS, Couture, P, Fonck, RJ, Gammel, G, Heidbrink, WW, Kaita, R, Kugel, HW, LeBlanc, B, Manickam, J, Ohyabu, N, Okabayashi, M, Reusch, MF, and Takahashi, H

Subjects
Atomic, Molecular, Nuclear, Particle and Plasma Physics, Fluids & Plasmas
Abstract

At low qψ (2.3 ≤ qψ ≤ 4.5), in the Princeton Beta Experiment, the discharges are limited by a hard disruption following the growth and sawtooth-like 'crash' of a ≤25 kHz precursor oscillation. The disruption, which occurs even in discharges with ⟨t⟨ well below the first stability regime boundary (2.5 μ0IpaBt), follows the crash of this precursor mode either immediately or with a delay of several milliseconds, with the immediate disruptions primarily occurring in the discharges with ⟨t⟩ close to the first regime limit. The highest ⟨t⟩ discharges also exhibit the fastest growth times and the highest level of edge MHD activity. Associated with the precursor mode crash is a loss of up to 30% of the plasma energy; thus, for non-zero delay shots, it is the crash and not the actual disruption that is the ⟨t⟩ limiting process. The delay period is interpreted as a period during which a locked mode, consisting of several toroidal components of comparable amplitude, grows. Because of the energy loss associated with the crash, the plasma goes vertically unstable during the delay period. The results of this study indicate that even within the relatively narrow low-qψ operating space, there is a continuum in the characteristics of the low-q^ disruptions with a primary dependence on the value of ⟨t⟩. While the ideal external kink instability may give rise to the growing oscillations that lead up to the ultimate disruption, the instabilities are weighted towards the edge only at the lowest qψ (≤3) and highest ⟨t⟩. The results of this study indicate that effects outside the scope of ideal MHD theory may play a significant role in low-qψ disruptions. © 1988 IOP Publishing Ltd.

Published
1988

65. High-temperature plasmas in a tokamak fusion test reactor

Author

Strachan, JD, Bitter, M, Ramsey, AT, Zarnstorff, MC, Arunasalam, V, Bell, MG, Bretz, NL, Budny, R, Bush, CE, Davis, SL, Dylla, HF, Efthimion, PC, Fonck, RJ, Fredrickson, E, Furth, HP, Goldston, RJ, Grisham, LR, Grek, B, Hawryluk, RJ, Heidbrink, WW, Hendel, HW, Hill, KW, Hsuan, H, Jaehnig, KP, Jassby, DL, Jobes, F, Johnson, DW, Johnson, LC, Kaita, R, Kampershroer, J, Knize, RJ, Kozub, T, LeBlanc, B, Levinton, F, La Marche, PH, Manos, DM, Mansfield, DK, McGuire, K, McNeill, DH, Meade, DM, Medley, SS, Morris, W, Mueller, D, Nieschmidt, EB, Owens, DK, Park, H, Schivell, J, Schilling, G, Schmidt, GL, Scott, SD, Sesnic, S, Sinnis, JC, Stauffer, FJ, Stratton, BC, Tait, GD, Taylor, G, Towner, HH, Ulrickson, M, von Goeler, S, Wieland, R, Williams, MD, Wong, K-L, Yoshikawa, S, Young, KM, and Zweben, SJ

Subjects
Mathematical Sciences, Physical Sciences, Engineering, General Physics
Abstract

Neutral-beam heating of plasmas in the Tokamak Fusion Test Reactor at low preinjection densities [ne(0)1019 m-3] were characterized by Te(0)=6.5 keV, Ti(0)=20 keV, ne(0)=7×1019 m-3, E=170 msec, theta=2, and a d(d,n)3He neutron emission rate of 1016 sec-1. The ion temperature and the deuterium-fusion neutron yields were significantly higher than for previous tokamak experiments. The low initial densities were achieved by operation of the Tokamak Fusion Test Reactor with low plasma currents (1 MA) and by extensive limiter conditioning. © 1987 The American Physical Society.

Published
1987

66. Tangential Neutral-Beam-Driven Instabilities in the Princeton Beta Experiment

Author

Heidbrink, WW, Bol, K, Buchenauer, D, Fonck, R, Gammel, G, Ida, K, Kaita, R, Kaye, S, Kugel, H, LeBlanc, B, Morris, W, Okabayashi, M, Powell, E, Sesnic, S, and Takahashi, H

Subjects
Mathematical Sciences, Physical Sciences, Engineering, General Physics
Abstract

During tangential neutral-beam injection into the PBX tokamak, bursts of two types of instabilities are observed. One instability occurs in the frequency range 120-210 kHz and the other oscillates predominantly near the frequency of bulk plasma rotation (20-30 kHz). Both instabilities correlate with drops in neutron emission and bursts in charge-exchange neutral flux, indicating that beam ions are removed from the center of the plasma by the instabilities. The central losses are comparable to the losses induced by the fishbone instability during perpendicular injection. © 1986 The American Physical Society.

Published
1986

67. Initial results from the scoop limiter experiment in PDX

Author

Budny, R, Bell, MG, Bol, K, Boyd, D, Buchenauer, D, Cavallo, A, Couture, P, Crowley, T, Darrow, DS, Dylla, HF, Fonck, RJ, Gilpin, R, Goldston, R, Grek, B, Heidbrink, W, Heifetz, D, Jaehnig, K, Johnson, D, Kaita, R, Kaye, SM, Knize, RJ, Kugel, H, LeBlanc, B, Manos, D, Mansfield, D, Mazzucato, E, McBride, T, McCann, R, McCune, D, McGuire, K, Mueller, D, Okabayashi, M, Okano, K, Owens, DK, Post, DE, Reusch, M, Schmidt, G, Sesnic, S, Slusher, D, Strachan, J, Surko, C, Takahashi, H, Tenney, F, Towner, H, Ulrickson, M, and Valley, J

Subjects
Energy, Materials Engineering
Abstract

A particle scoop limiter with a graphite face backed by a 50 liter volume for collecting particles was used in PDX. Experiments were performed to test its particle control and power handling capabilities with up to 5 MW of D° power injected into D+ plasmas. Line average plasma densities of up to 8 × 1013 cm-3 and currents up to 450 kA were obtained. Plasma densities in the scoop channels greater than 2 × 1013 cm-3 and neutral densities in the scoop volume greater than 5 × 1014 cm-3 were observed. There is evidence that recycling may have occurred in the scoop channels for several discharges with large line-averaged plasma density. At beam powers up to 2.5 MW, energy confinement times above 40 ms were deduced from magnetics measurements and from transport analysis. Pressures in the vacuum vessel were in the 10 -5 Torr range, and recycling source neutral densities in the central plasma were low. © 1984.

Published
1984

88. Simulation Of Microtearing Turbulence In NSTX

Author

Guttenfelder, W, primary, Kaye, S M, additional, Nevins, W M, additional, Wanag, E, additional, Zhang, J, additional, Bell, R E, additional, Crocker, N A, additional, Hammett, G W, additional, LeBlanc, B P, additional, Mikkelsen, D R, additional, and Ren, Y, additional

Published
2012
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89. L-H Threshold Studies in NSTX

Author

Kaye, S M, primary, Battaglia, D, additional, Bell, R E, additional, Chang, C S, additional, Hosea, J, additional, Kugel, H, additional, LeBlanc, B P, additional, Meyer, H, additional, and Park, G Y, additional

Published
2011
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98. Advances in High-harmonic Fast Wave Physics in the National Spherical Torus Experiment

Author

Taylor, G, primary, Hosea, J C, additional, LeBlanc, B P, additional, Phillips, C K, additional, Podesta, M, additional, Valeo, E J, additional, Wilson, J R, additional, Ahn, J -W, additional, Chen, G, additional, Green, D L, additional, Jaeger, E F, additional, Maingi, R, additional, Ryan, P M, additional, Wilgen, J B, additional, Heidbrink, W W, additional, Liu, D, additional, Bonoli, P T, additional, Brecht, T, additional, and Choi, M, additional

Published
2009
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