The distribution of ion energies incident on an ICRH (ion cyclotron resonant heating) antenna Faraday shield
In the thesis, plasma properties and ion energies were measured in the near field of an ICRH antenna to determine the effects of rf fields in a magnetized plasma sheath on the energy of ions incident on the surface of the Faraday shield. A resonant loop antenna with a two-tier Faraday shield was used on the RF Test Facility at Oak Ridge National Laboratory. The time-varying floating potential was measured with a capacitive probe and the time-averaged floating potential, electron temperature, and density were measured with a Langmuir probe. The measurements indicate that the plasma potential and electron temperature in front of the antenna clearly increase with antenna current and near field strength, and follow the rf magnetic field pattern of the antenna, indicating that the electromagnetic field is responsible for the potential formation. A computational model of a magnetized sheath with a time-varying sheath potential was developed to predict the distribution of ion energies at the shield surface, using measured data as input. The model results indicate that there will be a broadening in the distribution when the rf driving frequency approaches the local ion cyclotron frequency near the antenna. The broadening results in an increased population of ions with energies close to the maximum plasma potential. The experimental and computational results of this thesis strongly indicate that the impurity generation seen with high-power ICRH is a result of a change in the sheath potential and an increased electron temperature due to the plasma interaction with the antenna near field.
- Research Organization:
- Illinois Univ., Urbana, IL (USA)
- OSTI ID:
- 6134073
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
700205* -- Fusion Power Plant Technology-- Fuel
Heating
& Injection Systems
ANTENNAS
AUXILIARY HEATING
CONFINEMENT
ELECTRIC PROBES
ELECTRICAL EQUIPMENT
ELECTRON TEMPERATURE
EQUIPMENT
FARADAY EFFECT
FEASIBILITY STUDIES
HEATING
HIGH-FREQUENCY HEATING
ICR HEATING
INTERACTIONS
LANGMUIR PROBE
MATHEMATICAL MODELS
PLASMA CONFINEMENT
PLASMA HEATING
PLASMA SHEATH
PROBES
RF SYSTEMS
SHIELDS
SPACE HEATING
TEST FACILITIES
THERMONUCLEAR DEVICES