Ion cyclotron resonance heating of a tokamak plasma using an antenna without a Faraday shield

An experiment was performed on the TEXTOR tokamak which proves that the plasma can be heated by ion cyclotron resonance using antennas without a Faraday shield.The heating performance of the unshielded antenna was found to be similar to that of a shielded antenna.Although the radiated power was somewhat higher with the unshielded antenna, no impurity problems were encountered.These results are explained on the basis of radiofrequency sheath theory and by the almost perfect shielding of parallel electric fields by the plasma.Implementation criteria for unshielded antennas were obtained.ABSTRACT.Preliminary experiments in the TORE SUPRA tokamak using the ergodic divertor configuration have shown a strong effect on plasma impurities.The result is a decontamination of the central plasma which is due to a decreased carbon content.This is the consequence of a screening effect of the peripheral ergodic layer which is due to an important increase of the recycling impurity flux, as well as of a modification of the impurity source terms.