Floating potential measurements in the near field of an ion cyclotron resonance heating antenna
Large variations in the plasma potential can lead to large sheath potentials at the surface of the Faraday shield of an ion cyclotron resonance heating (ICRH) antenna. This sheath can accelerate ions to energies where sputtering is significant, resulting in impurity generation. The time-varying floating potential is being measured in the near field of an ICRH antenna by using the Radio Frequency Test Facility (RFTF) at Oak Ridge National Laboratory. The antenna used is a resonant loop antenna that has a two-tier Faraday shield with a layer of graphite on the outer tier. The electron cyclotron heated plasma in RFTF is produced by a 10.6-GHz klystron. The magnetic field at the antenna is /similar to/2 kG, with a plasma density of /similar to/10/sup 10/ cm/sup -3/ with an electron temperature of /similar to/6 eV. Ionization by rf power from the antenna produces a local plasma of /similar to/10/sup 11/ with an electron temperature of 12 to 20 eV. The rf floating potential is measured by using a capacitively coupled probe that is scanned in front of the antenna, parallel to the current strap. A stationary Langmuir probe is used to measure the time-averaged floating potential. Measurements indicate that the potential scales with the antenna current and increases with plasma density to values of up to 300 V peak-to-peak. The rf component of the floating potential seems to follow the near field pattern of the antenna, indicating that these fields may be responsible for the potential formation.
- Research Organization:
- Department of Nuclear Engineering, University of Illinois, Urbana, Illinois 61801
- OSTI ID:
- 6317292
- Journal Information:
- J. Vac. Sci. Technol., A; (United States), Vol. 7:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PLASMA HEATING
PLASMA DIAGNOSTICS
ANTENNAS
ELECTRIC FIELDS
ELECTRIC POTENTIAL
ELECTRON DENSITY
ELECTRON TEMPERATURE
EXPERIMENTAL DATA
FARADAY CUPS
ION CYCLOTRON-RESONANCE
LANGMUIR PROBE
MAGNETIC FIELDS
RF SYSTEMS
BEAM MONITORS
CYCLOTRON RESONANCE
DATA
ELECTRIC PROBES
ELECTRICAL EQUIPMENT
EQUIPMENT
HEATING
INFORMATION
MEASURING INSTRUMENTS
MONITORS
NUMERICAL DATA
PROBES
RESONANCE
700102* - Fusion Energy- Plasma Research- Diagnostics