Probe measurements of the density and temperature profiles in the JET plasma boundary

Abstract

A series of measurements of the plasma boundary parameters have been made on JET using an array of Langmuir probes and heat flux probes. The profiles decay exponentially, with typical e-folding lengths of 30–60 mm for the density and 50–100 mm for the temperature. The cross-field diffusion coefficient estimated from these data is 0.5–1 m2·s−1. Using the particle fluxes and energies, the calculated impurity production is generally consistent with that observed spectroscopically. The measured profiles have also been used to calculate the screening of impurities from the wall due to ionization in the boundary layer. It is found that metals from the wall are ionized in the boundary layer but are likely to be deposited on the limiter from where they will be re-sputtered into the plasma. The light impurities from the wall, such as carbon and oxygen, are not well screened. From the data, estimates of the electric field in the plasma have been made which indicate significant × drifts in the poloidal direction.