Observations of Lower Hybrid Wave Absorption in the Scrape Off Layer of a Diverted Tokamak

Journal Article · Thu Nov 26 00:00:00 EST 2009 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3273775· OSTI ID:21335752

Wallace, G M; Parker, R R; Bonoli, P T; Schmidt, A E; Whyte, D G; Wright, J C; Wukitch, S J ^[1]; Harvey, R W; Smirnov, A P ^[2]; Wilson, J R ^[3]

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1. MIT Plasma Science and Fusion Center, Cambridge, Massachusetts (United States)
2. CompX, Del Mar, California (United States)
3. Princeton Plasma Physics Laboratory, Princeton, New Jersey (United States)

The Lower Hybrid Current Drive (LHCD) system on Alcator C-Mod is designed to drive off-axis current in the core plasma, e.g. r/a{<=}0.8, however several interesting observations indicate that the LH waves are depositing significant power in the Scrape Off Layer (SOL) in high density L-Mode discharges. These phenomena are observed in accessible plasmas below the so-called 'density limit' attributed to Parametric Decay Instabilities as {omega}{yields}2{omega}{sub lh}. Parallel current densities of {approx}500 kA/m{sup 2} are measured on divertor Langmuir probes located just outside the separatrix during high power LH operation above n-bar{sub e}{approx}1x10{sup 20} m{sup -3}. These SOL currents rise at the same density at which the line integrated hard X-ray Bremsstrahlung emission drops sharply. Ray tracing/Fokker-Planck simulations over-estimate the line integrated X-ray emissivity by a factor of {approx}500 at n-bar{sub e} = 1.4 10{sup 20} m{sup -3} as compared to a factor of 3-4 at n-bar{sub e} = 0.6x10{sup 20} m. Ray tracing simulations including a realistic SOL show similar trends in X-ray emission compared with the experimental observations.

• OSTI ID: 21335752
• Journal Information: AIP Conference Proceedings, Vol. 1187, Issue 1; Conference: 18. topical conference on radio frequency power in plasmas, Gent (Belgium), 24-26 Jun 2009; Other Information: DOI: 10.1063/1.3273775; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALCATOR DEVICE
BREMSSTRAHLUNG
CURRENT DENSITY
DECAY INSTABILITY
DIVERTORS
EMISSIVITY
FOKKER-PLANCK EQUATION
HARD X RADIATION
LANGMUIR PROBE
L-MODE PLASMA CONFINEMENT
LOWER HYBRID CURRENT DRIVE
LOWER HYBRID HEATING
PLASMA
PLASMA DIAGNOSTICS
PLASMA SCRAPE-OFF LAYER
PLASMA SIMULATION
REACTOR ACCIDENT SIMULATION