Electron Bernstein Wave Research on NSTX and PEGASUS
- Princeton Plasma Physics Laboratory, Princeton, NJ (United States)
- Oak Ridge National Laboratory, Oak Ridge, TN (United States)
- University of Wisconsin-Madison, Madison, WI (United States)
- CompX, San Diego, CA (United States)
- Czech Institute of Plasma Physics (Czech Republic)
- Columbia University, New York, NY (United States)
Spherical tokamaks (STs) routinely operate in the overdense regime ({omega}{sub pe}>>{omega}{sub ce}), prohibiting the use of standard ECCD and ECRH. However, the electrostatic electron Bernstein wave (EBW) can propagate in the overdense regime and is strongly absorbed and emitted at the electron cyclotron resonances. As such, EBWs offer the potential for local electron temperature measurements and local electron heating and current drive. A critical challenge for these applications is to establish efficient coupling between the EBWs and electromagnetic waves outside the cutoff layer. Two STs in the U.S., the National Spherical Tokamak Experiment (NSTX, at Princeton Plasma Physics Laboratory) and PEGASUS Toroidal Experiment (University of Wisconsin-Madison) are focused on studying EBWs for heating and current drive. On NSTX, two remotely steered, quad-ridged antennas have been installed to measure 8-40 GHz (fundamental, second and third harmonics) thermal EBW emission (EBE) via the oblique B-X-O mode conversion process. This diagnostic has been successfully used to map the EBW mode conversion efficiency as a function of poloidal and toroidal angles on NSTX. Experimentally measured mode conversion efficiencies of 70{+-}20% have been measured for 15.5 GHz (fundamental) emission in L-mode discharges, in agreement with a numerical EBE simulation. However, much lower mode conversion efficiencies of 25{+-}10% have been measured for 25 GHz (second harmonic) emission in L-mode plasmas. Numerical modeling of EBW propagation and damping on the very-low aspect ratio PEGASUS Toroidal Experiment has been performed using the GENRAY ray-tracing code and CQL3D Fokker-Planck code in support of planned EBW heating and current drive (EBWCD) experiments. Calculations were performed for 2.45 GHz waves launched with a 10 cm poloidal extent for a variety of plasma equilibrium configurations. Poloidal launch scans show that driven current is maximum when the poloidal launch angle is between 10 and 25 degrees, supporting a launcher placed near the midplane. Current was driven on axis primarily via the Fisch-Boozer mechanism. The PEGASUS experiment provides an attractive opportunity to investigate EBW heating and current drive physics at the fundamental electron cyclotron frequency in an ST plasma, and will complement the EBW research planned for NSTX.
- OSTI ID:
- 21032785
- Journal Information:
- AIP Conference Proceedings, Vol. 933, Issue 1; Conference: 17. topical conference on radio frequency power in plasmas, Clearwater, FL (United States), 7-9 May 2007; Other Information: DOI: 10.1063/1.2800504; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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Investigation of electron Bernstein wave (EBW) coupling and its critical dependence on EBW collisional loss in high-beta, H-mode ST plasmas
Related Subjects
ANTENNAS
ASPECT RATIO
BERNSTEIN MODE
COMPUTERIZED SIMULATION
ECR CURRENT DRIVE
ECR HEATING
ELECTRIC CURRENTS
ELECTROMAGNETIC RADIATION
ELECTRON CYCLOTRON-RESONANCE
ELECTRON TEMPERATURE
ELECTRONS
FOKKER-PLANCK EQUATION
GHZ RANGE
HARMONICS
L-MODE PLASMA CONFINEMENT
MODE CONVERSION
NSTX DEVICE
PLASMA
PLASMA SIMULATION
PLASMA WAVES