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jpl_epr_2014_noextraslides.pdf2014-08-14 09:02:48Jeffrey Levesque

Active and passive MHD stability research on the HBT-EP tokamak

Author: Jeffrey P Levesque
Requested Type: Consider for Invited
Submitted: 2014-05-30 10:17:16

Co-authors: P.E. Hughes, P.J. Byrne, Q. Peng, S. Angelini, J. Bialek, C.J. Hansen, M.E. Mauel, G.A. Navratil, D.J. Rhodes, C.C. Stoafer

Contact Info:
Columbia University
500 West 120th St., room 102
New York, NY   10027
United States

Abstract Text:
We present an overview of ongoing MHD stability research on the High Beta Tokamak -- Extended Pulse (HBT-EP) device [1]. Passive and active studies are conducted using high-resolution sets of magnetic sensors and 3D control coils. A Graphics Processing Unit (GPU)-based controller allows high-throughput, massively-parallel computations in feedback algorithms [2]. The 3D response to applied non-axisymmetric fields is studied with an adjustable ferromagnetic wall and with a variable equilibrium poloidal cross-section. Ferritic tiles (mu/mu_0 = 8) have been added to the plasma-facing side of half of the in-vessel movable wall segments in HBT-EP in order to explore Ferromagnetic Resistive Wall Mode (FRWM) stability [3]. Plasma-wall separation for alternating ferritic and non-ferritic wall segments is adjusted between discharges without opening the vacuum vessel. Amplification of applied resonant fields is observed to be at least twice as strong when the ferromagnetic wall is close to plasma surface (r/a ~ 1.07) instead of the standard stainless steel wall, and disruptivity is increased. Experiments with rapidly rotating external kink modes show wall stabilization in the presence of the close ferritic wall, extending previous observations [4]. A biased electrode is used to inject torque and strongly modify the plasma rotation. Plasmas with slowly rotating modes are expected to have reduced wall stabilization due to ferritic effects. Resonant fields are also applied while the plasma transitions from circular limited cross-sections to shaped, single-null cross-sections. Diverted plasmas are dominated by a single mode as the edge helicity resonance is removed, in agreement with DCON predictions.

[1] J. P. Levesque et al., Nuclear Fusion 53, 073037 (2013)
[2] N. Rath et al., Nuclear Fusion 53, 073052 (2013)
[3] V. D. Pustovitov and V. V. Yanovskiy, Physics of Plasmas 21, 022516 (2014)
[4] K. Tsuzuki et al., Nuclear Fusion 46, 966 (2006)

Characterization: 1.0,3.0

Comments:

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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