Abstract
Multi-megawatt Ion Cyclotron Range of Frequencies (ICRF) heating is routinely used in the JET tokamak. To increase the ICRF heating power available from the A2 antennas, the ICRF ITER-Like Antenna (ILA) was reinstalled for the 2015 JET ITER-like wall experimental campaign. The application of high levels of ICRF power typically results in increased plasma wall interaction which leads to the observation of enhanced influx of metallic impurities in the plasma edge. It is assumed that the impurity production is mainly driven by the parallel component of the Radio-Frequency (RF) antenna electric near-field, E// (parallel to the confinement magnetic field of the tokamak), that is rectified in a thin boundary layer (RF sheath). Torino Polytechnic Ion Cyclotron Antenna (TOPICA) code was used to compute E// field maps in front of the ILA and between its poloidal limiters in the presence of plasma using measured density profiles and various antenna feedings. E// field maps calculated between the poloidal limiters were used to estimate the poloidal distribution of RF-sheath Direct Current (DC) potential in this private region of the ILA and make relative comparison of various antenna electrical settings. For this purpose we used the asymptotic version of the Self-consistent Sheaths and Waves for Ion Cyclotron Heating Slow-Wave (SSWICH-SW) code. These estimations can help to study the formation of RF sheaths around the antenna and even at distant locations (∼3m away).
Highlights
Multi-megawatt Ion Cyclotron Range of Frequencies (ICRF) heating with four A2 antennae is routinely used in the JET tokamak
Application of high levels of ICRF power typically results in increased plasma wall interaction which leads to observation of enhanced influx of metallic impurities in the plasma edge [4]
With the ITER-like wall (ILW), the ITER-Like Antenna (ILA) operation with only bottom half array powered leads to improvement of around 20% in terms of lower radiated power from the bulk plasma and the RFinduced tungsten content compared to A2 antennas operations
Summary
Multi-megawatt Ion Cyclotron Range of Frequencies (ICRF) heating with four A2 antennae is routinely used in the JET tokamak. E// field maps calculated between the poloidal limiters were used to estimate poloidal distribution of RF-sheath DC potential VDC in this private region of the ILA For this purpose we used the asymptotic version of the Self-consistent Sheaths and Waves for Ion Cyclotron Heating Slow-Wave (SSWICH-SW) code with radiating boundary conditions [10]. These estimations can help to study the formation of RF sheaths around the antenna and even at distant locations (~3m away) and make association to some variations of the Be line emission that were measured spectroscopically on some of the A2 antenna limiters when the magnetic connection from observation point to the active ILA was moved via a q95 scan [7]
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