Electron Bernstein wave emission based diagnostic on National Spherical Torus Experiment (invited)

Conference · Tue Jan 01 04:00:00 EST 2008

OSTI ID:1015048

Diem, S. ^[1]; Taylor, G. ^[1]; Caughman, John B ^[2]; Efthimion, P. C. ^[1]; Kugel, H. ^[1]; LeBlanc, B ^[1]; Preinhaelter, J. ^[3]; Sabbagh, S. A. ^[4]; Urban, J ^[3]

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1. Princeton Plasma Physics Laboratory (PPPL)
2. ORNL
3. Institute of Plasma Physics, Prague, Czech Republic
4. Columbia University

National Spherical Torus Experiment (NSTX) is a spherical tokamak (ST) that operates with n(e) up to 10(20) m(-3) and B-T less than 0.6 T, cutting off low harmonic electron cyclotron (EC) emission widely used for T-e measurements on conventional aspect ratio tokamaks. The electron Bernstein wave (EBW) can propagate in ST plasmas and is emitted at EC harmonics. These properties suggest thermal EBW emission (EBE) may be used for local T-e measurements in the ST. Practically, a robust T-e(R,t) EBE diagnostic requires EBW transmission efficiencies of >90% for a wide range of plasma conditions. EBW emission and coupling physics were studied on NSTX with an obliquely viewing EBW to O-mode (B-X-O) diagnostic with two remotely steered antennas, coupled to absolutely calibrated radiometers. While T-e(R,t) measurements with EBW emission on NSTX were possible, they were challenged by several issues. Rapid fluctuations in edge n(e) scale length resulted in >20% changes in the low harmonic B-X-O transmission efficiency. Also, B-X-O transmission efficiency during H modes was observed to decay by a factor of 5-10 to less than a few percent. The B-X-O transmission behavior during H modes was reproduced by EBE simulations that predict that EBW collisional damping can significantly reduce emission when T-e < 30 eV inside the B-X-O mode conversion (MC) layer. Initial edge lithium conditioning experiments during H modes have shown that evaporated lithium can increase T-e inside the B-X-O MC layer, significantly increasing B-X-O transmission.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1015048
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ANTENNAS
ASPECT RATIO
CYCLOTRONS
DAMPING
DECAY
EFFICIENCY
ELECTRONS
FLUCTUATIONS
HARMONICS
LITHIUM
MODE CONVERSION
PHYSICS
PLASMA
PLASMA DIAGNOSTICS
RADIOMETERS