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Title: Scenario Development During Commissioning Operations on the National Spherical Torus Experiment Upgrade
Contributors: Battaglia, D.J.
Boyer, M.D.
Gerhardt, S.
Mueller, D.
Myers, C.E.
Guttenfelder, W.
Menard, J.E.
Sabbagh, S.A.
Scotti, F.
Bedoya, F.
Bell, R.E.
Berkery, J.W.
Diallo, A.
Ferraro, N.
Jaworski, M.A.
Kaye, S.M.
LeBlanc, B.P.
Ono, M.
Park, J.-K.
Podesta, M.
Raman, R.
Soukhanovskii, V.A.
U. S. Department of Energy contract number DE-AC02-09CH11466
Keywords: Scenario development
Real-time control
Spherical tokamak
Wall conditioning
Tokamak startup
Error field correction
Issue Date: Apr-2018
Publisher: Princeton Plasma Physics Laboratory, Princeton University
Related Publication: Nuclear Fusion vol. 58 p. 046010 (April 2018)
Abstract: The National Spherical Torus Experiment Upgrade (NSTX-U) will advance the physics basis required for achieving steady-state, high-beta, and high-confinement conditions in a tokamak by accessing high toroidal field (1 T) and plasma current (1.0 - 2.0 MA) in a low aspect ratio geometry (A = 1.6 - 1.8) with flexible auxiliary heating systems (12 MW NBI, 6 MW HHFW). This paper describes progress in the development of L- and H-mode discharge scenarios and the commissioning of operational tools in the first ten weeks of operation that enable the scientific mission of NSTX-U. Vacuum field calculations completed prior to operations supported the rapid development and optimization of inductive breakdown at different values of ohmic solenoid current. The toroidal magnetic field (B_T0 = 0.65 T) exceeded the maximum values achieved on NSTX and novel long-pulse L-mode discharges with regular sawtooth activity exceeded the longest pulses produced on NSTX (tpulse > 1.8s). The increased flux of the central solenoid facilitated the development of stationary L-mode discharges over a range of density and plasma current (Ip). H-mode discharges achieved similar levels of stored energy, confinement (H98y,2 > 1) and stability (beta_N/beta_N-nowall > 1) compared to NSTX discharges for Ip < 1 MA. High-performance H-mode scenarios require an L-H transition early in the Ip ramp-up phase in order to obtain low internal inductance (li) throughout the discharge, which is conducive to maintaining vertical stability at high elongation (kappa > 2.2) and achieving long periods of MHD quiescent operations. The rapid progress in developing L- and H-mode scenarios in support of the scientific program was enabled by advances in real-time plasma control, efficient error field identification and correction, effective conditioning of the graphite wall and excellent diagnostic availability.
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Appears in Collections:NSTX-U

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