Plasma‐edge studies using carbon resistance probes

Characterization of erosion and hydrogen‐recycling processes occurring at the edge of magnetically confined plasmas requires knowledge of the energy and flux of hydrogen isotopes incident on the materials. A new plasma‐edge probe technique, the carbon resistance probe, has been developed to obtain this information. This technique utilizes the increase in electrical resistance caused in thin carbon films by energetic particle bombardment to characterize the flux and energy of the incident ions and neutrals. The method is relatively easy to implement and gives data in real time. Energy resolution of low dose exposures has been achieved using thin insulating films over the carbon. Calibrations using ion implantation show that the particle energies and fluxes which can be measured with resistance probes are well matched to those typically encountered near the wall in plasma devices. This paper describes the experimental technique and the model used to relate the measured resistance changes to the energy and flux of particles. Experiments are then described in which resistance probes were used to study energetic particles in the PLT and TEXTOR tokamaks and the TMX‐U tandem mirror.