Design of an ICRH antenna for RF-plasma interaction studies

The interaction between an ion cyclotron resonant heating antenna and the near-field plasma can lead to rectified (high voltage) sheath formation and subsequent material erosion. This issue will be studied by using a simple loop antenna operated on the Physics Integration eXperiment (PhIX) at ORNL, which is a linear plasma device that uses an ECH heated helicon plasma source to create a high-density plasma suitable for use in a plasma-material interaction test stand. The antenna consists of a single strap with a single-tier Faraday shield. The antenna is $\sim $one-quarter wavelength long at 50 MHz and grounded at one end, which will allow for strap voltages of $>$20 kV to be located near the plasma. The PhIX edge plasma near the antenna is similar to typical edge conditions, with n$_{e}\sim $1-2x10$^{18}$/m$^{3}$ and T$_{e}$=5-10 eV, with a magnetic field of 0.1-0.2 Tesla. Several diagnostics will be used to characterize the near-field interaction, including Langmuir and capacitive probes, energy analyzers, Stark effect spectroscopy, and local/remote material erosion measurements. Details of the antenna design and initial characterization will be presented.