An assessment of the lifetime of Faraday shield elements

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5837612

Ruzic, D N ^[1]; Hoffman, D J; Langley, R A; Lewis, M B; Ryan, P M ^[2]

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1. Illinois Univ., Urbana, IL (USA)
2. Oak Ridge National Lab., TN (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 a Langmuir probe. Ion energies were measured with a gridded energy analyser located below the antenna, and samples of silicon were placed on the Faraday shield surface to estimate the incident ion energy. The capacitive probe measurements 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. Plasma parameters and ion energies have been correlated with the antenna current and used in a computational model of the plasma sheath to predict the amount of erosion expected from the Faraday shield elements exposed to plasma. Predictions of light ion sputtering of candidate Faraday shield materials are presented.

• Research Organization: Oak Ridge National Lab., TN (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5837612
• Report Number(s): CONF-9009381-1; ON: DE91012228
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700205* -- Fusion Power Plant Technology-- Fuel
Heating
& Injection Systems
ANTENNAS
CARBON
ELECTRIC PROBES
ELECTRICAL EQUIPMENT
ELECTRON TEMPERATURE
ELEMENTAL MINERALS
ELEMENTS
EQUIPMENT
EROSION
GRAPHITE
HEATING
HIGH-FREQUENCY HEATING
ICR HEATING
LANGMUIR PROBE
MINERALS
NONMETALS
PLASMA HEATING
PROBES
SERVICE LIFE
SHIELDING
SPUTTERING