An assessment of the lifetime of Faraday shield elements

Conference · Sun Jan 01 00:00:00 EST 1989

OSTI ID:5327229

Ruzic, D N; Hoffman, D J; Langley, R A; Lewis, M B; Ryan, P M ^[1]

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1. Illinois Univ., Urbana, IL (USA)

The interaction of plasma with rf fields from an ion cyclotron range of frequencies (ICRF) antenna has been studied to estimate the amount of Faraday shield erosion expected in normal ICRF heating operation. Plasma parameters and ion energies have been measured in the near field of an antenna and used in a model to estimate the erosion rate of the Faraday shield surface. Experiments were conducted on the RF Test Facility, a magnetic mirror device at Oak Ridge National Laboratory, using a single-strap resonant loop antenna with a two-tier Faraday shield. The outer tier, facing the plasma, was layered with graphite tiles. The antenna was operated at currents and voltages within 50% of those expected in tokamaks. The time-varying floating potential was measured with a capacitively coupled probe, and the time-averaged floating potential, electron temperature, and electron density were measured with Langmuir probe. Both probes were scanned in front of the antenna. Ion energies were measured with a gridded energy analyzer located below the antenna, and samples of silicon were placed on the Faraday shield surface to estimate the incident ion energy. The capacitive probe measurement show that the rf floating potential follows the magnetic field pattern of the antenna, indicating that the electromagnetic fields are responsible for the potential formation. Electron temperatures increase with rf power and can reach values {ge}60 eV for an rf power of {approximately}25 kW. Incident ion energies {ge}300 eV have been measured for the same power level. Predictions of light ion sputtering of candidate Faraday shield materials are presented. 19 refs., 6 figs., 1 tab.

• Research Organization: Oak Ridge National Lab., TN (USA)
• Sponsoring Organization: DOE/ER
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5327229
• Report Number(s): CONF-891007-83; ON: DE90002714; CNN: 19X-SB359V; TRN: 89-029865
• Resource Relation: Conference: 13. international symposium on fusion engineering, Knoxville, TN (USA), 2-6 Oct 1989
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ANTENNAS
MAGNETIC SHIELDING
ELECTRON DENSITY
ELECTRON TEMPERATURE
EROSION
ICR HEATING
LANGMUIR PROBE
MAGNETIC FIELD CONFIGURATIONS
SPUTTERING
SURFACES
TOKAMAK DEVICES
CLOSED PLASMA DEVICES
ELECTRIC PROBES
ELECTRICAL EQUIPMENT
EQUIPMENT
HEATING
HIGH-FREQUENCY HEATING
PLASMA HEATING
PROBES
SHIELDING
THERMONUCLEAR DEVICES
700205* - Fusion Power Plant Technology- Fuel
Heating
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