Ion energy and plasma measurements in the near field of an ICRF antenna

Abstract

Plasma properties and ion energies have been measured in the near field of an ICRF 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 (ORNL). The magnetic field near the antenna is ∼2 kG, and the plasma density is ∼1011 cm−3 with an electron temperature of 6–10 eV. The time‐varying floating potential was measured with a capacitively coupled probe, and the time‐averaged electron temperature electron density, and floating potential were measured with a Langmuir probe. Both probes were canned poloidally in front of the antenna, parallel to the current strap. Diagnostic for measuring ion energies included a gridded energy analyzer located directly below the antenna. Measured ion energies are compared with predictions from a computational model for determining the energy and angular distibution of i...