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

Journal Article · Wed Oct 15 04:00:00 EDT 2008 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.2953592· OSTI ID:21266593

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

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1. Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 (United States)
2. Fusion Energy Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6169 (United States)
3. EURATOM/IPP.CR Association, Institute of Plasma Physics, 18200 Prague 8 (Czech Republic)
4. Department of Applied Physics and Applied Mathematics, Columbia University, New York 10027 (United States)

National Spherical Torus Experiment (NSTX) is a spherical tokamak (ST) that operates with n{sub e} up to 10{sup 20} m{sup -3} and B{sub T} less than 0.6 T, cutting off low harmonic electron cyclotron (EC) emission widely used for T{sub 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{sub e} measurements in the ST. Practically, a robust T{sub 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{sub e}(R,t) measurements with EBW emission on NSTX were possible, they were challenged by several issues. Rapid fluctuations in edge n{sub 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{sub 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{sub e} inside the B-X-O MC layer, significantly increasing B-X-O transmission.

• OSTI ID: 21266593
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 10 Vol. 79; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ANTENNAS
ASPECT RATIO
BERNSTEIN MODE
BOUNDARY LAYERS
CYCLOTRONS
EFFICIENCY
ELECTRONS
EMISSION
FLUCTUATIONS
H-MODE PLASMA CONFINEMENT
LITHIUM
NSTX DEVICE
PLASMA
PLASMA WAVES
RADIOMETERS
SPHERICAL CONFIGURATION
TRANSMISSION