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(EX/P2-12) Application of Electron Bernstein Wave Heating and Current Drive to High Beta Plasmas

P.C. Efthimion¹⁾, G. Taylor¹⁾, B. Jones¹⁾, R.W. Harvey⁴⁾, A.K. Ram³⁾, P. Smirnov⁵⁾, T. Munsat¹⁾, G. Bell²⁾, A. Bers³⁾, J. Decker³⁾, J.C. Hosea¹⁾, R. Kaita¹⁾, N. Lashmore-Davies⁶⁾, R. Majeski¹⁾, D.A. Rasmussen²⁾, J. Spaleta¹⁾, J. Wilgen²⁾, J.R. Wilson^1)
 
1) Princeton Plasma Physics Laboratory, Princeton, USA
²⁾ Oak Ridge National Laboratory, Oak Ridge, TN, U.S.A.
³⁾ Plasma Science and Fusion Center, M.I.T., Cambridge, MA, U.S.A.
⁴⁾ CompX, Del Mar, CA, U.S.A.
⁵⁾ Moscow State University, Moscow, Russia
⁶⁾ Euratom - UKAEA Fusion Assoc., Culham Science Centre, Abingdon, Oxon, U K.

Abstract.  Electron Bernstein Waves (EBW) can potentially heat and drive current in high-beta plasmas. Electomagnetic waves can convert to EBW via two paths. O-mode heating, demonstrated on W-7AS, requires waves be launched within a narrow k-parallel range. Alternately, in high-beta plasmas, the X-mode cutoff and EBW conversion layers are millimeters apart, so the fast X-mode can tunnel to the EBW branch. We are studying the conversion of EBW to the X-mode by measuring the radiation temperature of the cyclotron emission and comparing it to the electron temperature. In addition, mode conversion has been studied with an approximate kinetic full-wave code. We have enhanced EBW mode conversion to $\sim$ 100% by encircling the antenna with a limiter that shortens the density scale length at the conversion layer in the scrape off of the CDX-U spherical torus (ST) plasma. Consequently, a limiter in front of a launch antenna achieves efficient X-mode coupling to EBW. Ray tracing and Fokker-Planck codes have been used to develop current drive scenarios in NSTX high-beta ($\sim$ 40%) ST plasmas and a relativistic code will examine the potential synergy of EBW current drive with the bootstrap current.

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