Hybrid MHD Model for a Driven, Ion-Current FRC

Feasibility Study of Microwave Electron Heating on the C-2 Field-Reversed Configuration Device
Xiaokang Yang1, a), Alf Koehn2, Yuri Petrov3, Francesco Ceccherini1, Sean Dettrick1, Michl Binderbauer1, and the TAE Team
1Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, CA 92688, USA 2IGVP, University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany 3CompX, P.O. Box 2672, Del Mar, CA 92014, USA.
a)Corresponding author: xyang@trialphaenergy.com
Abstract. Different microwave heating scenarios for the C-2 plasmas have been investigated recently with use of both the Genray ray-racing code and the IPF-FDMC full-wave code, and the study was focused on the excitation of the electron Bernstein wave (EBW) with O-mode launch. For a given antenna position on C-2 and the fixed 2D plasma density and equilibrium field profiles, simulations have been done for six selected frequencies (2.45 GHz, 5 GHz, 8 GHz, 18 GHz, 28 GHz, and 50 GHz). Launch angles have been optimized for each case in order to achieve high coupling efficiencies to the EBW by the O-X-B mode conversion process and high power deposition. Results show that among those six frequencies, the case of 8 GHz is the most promising scenario, which has both high mode conversion efficiency (90%) and the relatively deeper power deposition.
INTRODUCTION
The FRC is a compact toroid (CT) formed with poloidal magnetic fields and zero or small self-generated toroidal fields [1]. The C-2 experiment [2] has adopted a collision-merging FRC formation scheme by colliding two high- CTs at a supersonic speed, each formed by a conventional theta-pinch. This collision-merging technique enables production of high temperature FRCs with radius rs 0.35 m, length ls 3 m, density ne 5 1019 m-3, total temperature Tt = Ti + Te up to 1 keV, external magnetic field Be 0.1 T, plasma current Ip 0.5 MA,
2 0 p Be2 ~ 90%, as expected for an FRC.
The plasma in C-2 is highly over-dense, with ɷpe ≫ ɷce inside the separatrix layer; this characteristic combined with FRC magnetic configuration makes it impossible to use conventional ECR for electron heating. One method that might overcome this limitation is to use EBW, which has no high-density cut-off and is very well absorbed at fundamental ECR and its low harmonic layers [3]. This paper reports recent study of microwave heating for the C-2 device with the focus on coupling externally injected electromagnetic waves to EBWs. To investigate different heating scenarios and assess their efficiencies, simulations have been performed with both ray tracing code Genray and the full-wave code IPF-FDMC [4]. Different heating scenarios are examined by varying microwave frequency and the launch angle, whereas plasma density profiles and background magnetic field are kept constant. Since both Genray and IPF-FDMC codes give similar results, only Genray simulations are briefly reported in this paper.
THE C-2 CONFIGURATION AND PARAMETERS
The C-2 device consists of a central confinement vessel which has cylindrical shape wall with about 4 m in length and 0.7 m in radius, as shown in Fig. 1 (a) and (b). The center of an available port for EBW heating is located at Z = -0.66 m, here z is the axial coordinate (Z = 0 is at the mid-plane) and it has same direction as the external
Radio Frequency Power in Plasmas
AIP Conf. Proc. 1689, 090008-1–090008-4; doi: 10.1063/1.4936545 © 2015 AIP Publishing LLC 978-0-7354-1336-8/$30.00
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