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(OV/4-3) Overview of Improved Confinement and Plasma Control in the MST Reversed Field Pinch

J.S. Sarff¹⁾, A.F. Almagri¹⁾, J.K. Anderson¹⁾, T.M. Biewer¹⁾, A.P. Blair¹⁾, D.L. Brower²⁾, M.D. Carter³⁾, M. Cengher¹⁾, B.E. Chapman¹⁾, P.K. Chattopadhyay¹⁾, V.I. Davydenko⁶⁾, D.J. Den Hartog¹⁾, W.X. Ding²⁾, F. Ebrahimi¹⁾, G. Fiksel¹⁾, C.B. Forest¹⁾, J.A. Goetz¹⁾, R.W. Harvey⁴⁾, D. Holly¹⁾, B. Hudson¹⁾, A.A. Ivanov⁶⁾, T.W. Lovell¹⁾, K.J. McCollam¹⁾, P.D. Nonn¹⁾, R. O’Connell¹⁾, S.P. Oliva¹⁾, R.I. Pinsker⁵⁾, S.C. Prager¹⁾, J.C. Reardon¹⁾, S.D. Terry¹⁾, M.A. Thomas¹⁾, M.D. Wyman¹⁾, C. Xiao⁷⁾, MST Team^1)
 
1) University of Wisconsin-Madison, Madison, WI, USA ²⁾ Electrical Engineering Department, University of California, Los Angeles, California USA
³⁾ Oak Ridge National Laboratory, Oak Ridge, Tennessee USA
⁴⁾ CompX, Del Mar, California USA
⁵⁾ General Atomic, LaJolla, California USA
⁶⁾ Budker Institute of Nuclear Physics, Novosibirsk Russia
⁷⁾ University of Saskatchewan, Saskatoon, Saskatchewan Canada

Abstract.  We present an overview of the MST program’s achievement of record performance for RFP plasmas and initiation of plasma control via rf current drive, neutral beam heating, and innovative inductive current drive. Magnetic transport is reduced via optimized inductive programming for J(r) control. The electron temperature nearly triples and beta doubles. The confinement time increases ten-fold (to $\sim$10 ms), which is comparable to L/H-mode scaling values for a tokamak with the same current and heating. Fast electron confinement is evidenced by hard x-ray emission. Fokker-Planck modeling requires the electron diffusivity be velocity-independent to reproduce the x-ray spectrum, implying the residual transport is not magnetic stochasticity. To extend profile control, rf current drive and neutral beam heating are in development. Low power observations include (1) neutral beam injected fast ions slow down classically, (2) lower hybrid waves propagate in high dielectric RFP plasmas, and (3) EBW emission is detected at blackbody levels, implying possible efficient injection. Oscillating Field Current Drive (dc current sustainment using sinusoidal inductive loop voltages) is also being tested.

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