Experimental Investigation of RF Sheath Rectification in ICRF and LH Heated Plasmas on Alcator C-Mod

Journal Article · Fri Dec 23 00:00:00 EST 2011 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3664961· OSTI ID:21612480

Ochoukov, R; Whyte, D G; Faust, I; LaBombard, B; Lipschultz, B; Meneghini, O; Wallace, G; Wukitch, S ^[1]; Myra, J ^[2]

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1. MIT Plasma Science and Fusion Center, Cambridge (United States)
2. Lodestar Research Corporation, Boulder, Colorado (United States)

Radio frequency (RF) rectification of the plasma sheath is being actively studied on C-Mod as a likely mechanism that leads to prohibitively high molybdenum levels in the plasma core of ion cyclotron RF (ICRF) heated discharges. We installed emissive, ion sensitive, Langmuir, and 3-D B-dot probes to quantify the plasma potentials ({Phi}{sub P}) in ICRF and lower hybrid (LH) heated discharges. Two probe sets were mounted on fixed limiter surfaces and one set of probes was mounted on a reciprocating (along the major radius) probe. Initial results showed that RF rectification is strongly dependent on the local plasma density and not on the local RF fields. The RF sheaths had a threshold-like appearance at the local density of {approx}10{sup 16} m-{sup 3}. Radial probe scans revealed that the RF sheaths peaked in the vicinity of the ICRF limiter surface, agreeing with a recent theory. The highest {Phi}{sub P}'s were observed on magnetic field lines directly mapped to the active ICRF antenna. Measurements in LH heated plasmas showed a strong {Phi}{sub P} dependence on the parallel index of refraction n{sub ||} of the launched LH waves: {Phi}{sub P} is greater at lower n{sub ||}. Little dependence was observed on the local plasma density.

• OSTI ID: 21612480
• Journal Information: AIP Conference Proceedings, Vol. 1406, Issue 1; Conference: 9. topical conference on radio frequency power in plasmas, Newport (United States), 1-3 Jun 2011; Other Information: DOI: 10.1063/1.3664961; (c) 2011 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
ANTENNAS
ELECTRIC DISCHARGES
ICR HEATING
ION CYCLOTRON-RESONANCE
IONS
LIMITERS
LOWER HYBRID CURRENT DRIVE
LOWER HYBRID HEATING
MAGNETIC FIELDS
MOLYBDENUM
PLASMA
PLASMA DENSITY
PLASMA POTENTIAL
PLASMA SHEATH
PLASMA WAVES
PROBES
RADIOWAVE RADIATION
REFRACTIVE INDEX
SURFACES
CHARGED PARTICLES
CLOSED PLASMA DEVICES
CYCLOTRON RESONANCE
ELECTRIC POTENTIAL
ELECTRICAL EQUIPMENT
ELECTROMAGNETIC RADIATION
ELEMENTS
EQUIPMENT
HEATING
HIGH-FREQUENCY HEATING
METALS
NON-INDUCTIVE CURRENT DRIVE
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PLASMA HEATING
RADIATIONS
REFRACTORY METALS
RESONANCE
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TRANSITION ELEMENTS