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Title: Electron Bernstein Wave Research on NSTX and PEGASUS

Abstract

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 efficienciesmore » 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.« less

Authors:
;  [1]; ; ; ;  [2];  [3];  [4]; ;  [5];  [6]
  1. Princeton Plasma Physics Laboratory, Princeton, NJ (United States)
  2. Oak Ridge National Laboratory, Oak Ridge, TN (United States)
  3. University of Wisconsin-Madison, Madison, WI (United States)
  4. CompX, San Diego, CA (United States)
  5. Czech Institute of Plasma Physics (Czech Republic)
  6. Columbia University, New York, NY (United States)
Publication Date:
OSTI Identifier:
21032785
Resource Type:
Journal Article
Journal Name:
AIP Conference Proceedings
Additional Journal Information:
Journal Volume: 933; Journal 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); Journal ID: ISSN 0094-243X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 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

Citation Formats

Diem, S J, LeBlanc, B P, Taylor, G, Caughman, J B, Bigelow, T, Wilgen, J B, Garstka, G D, Harvey, R W, Preinhaelter, J, Urban, J, and Sabbagh, S A. Electron Bernstein Wave Research on NSTX and PEGASUS. United States: N. p., 2007. Web. doi:10.1063/1.2800504.
Diem, S J, LeBlanc, B P, Taylor, G, Caughman, J B, Bigelow, T, Wilgen, J B, Garstka, G D, Harvey, R W, Preinhaelter, J, Urban, J, & Sabbagh, S A. Electron Bernstein Wave Research on NSTX and PEGASUS. United States. https://doi.org/10.1063/1.2800504
Diem, S J, LeBlanc, B P, Taylor, G, Caughman, J B, Bigelow, T, Wilgen, J B, Garstka, G D, Harvey, R W, Preinhaelter, J, Urban, J, and Sabbagh, S A. Fri . "Electron Bernstein Wave Research on NSTX and PEGASUS". United States. https://doi.org/10.1063/1.2800504.
@article{osti_21032785,
title = {Electron Bernstein Wave Research on NSTX and PEGASUS},
author = {Diem, S J and LeBlanc, B P and Taylor, G and Caughman, J B and Bigelow, T and Wilgen, J B and Garstka, G D and Harvey, R W and Preinhaelter, J and Urban, J and Sabbagh, S A},
abstractNote = {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.},
doi = {10.1063/1.2800504},
url = {https://www.osti.gov/biblio/21032785}, journal = {AIP Conference Proceedings},
issn = {0094-243X},
number = 1,
volume = 933,
place = {United States},
year = {2007},
month = {9}
}