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Part of the plasma current in a tokamak can be driven by lower hybrid (LH) waves. If such waves are launched in the direction of the electron drift, they produce a suprathermal tail in the electron distribution function by quasi-linear Landau damping. An 8 MW / 3.7 GHz LH launching system has been installed in Tore Supra. During long pulses experiments with lower hybrid current drive (LHCD), fast electrons with a large perpendicular energy can be toroidally trapped in the magnetic mirror, due to the finite number of coils. This phenomenon can be observed in a large peripheral zone of the plasma. Trapped electrons above a given energy are collisionless and are lost to the wall during their vertical drift motion. Such a phenomenon is likely to produce power losses during LHCD and first wall damages in the plasma vessel. The Fokker-Planck equation for the electron distribution function is solved using the Green's function technique and the method of images, in order to take into account the specific boundary conditions introduced by the existence of a loss cone in phase space. The first results obtained with a numerical code based on this theoretical model are in fair agreement with experimental data given by a diagnostic which measures the electron losses. From this data, it is estimated that a few percent of the injected power can be lost, and the average energy of the lost electrons is about 100 keV.

Additional information

Authors: CARRASCO J ET AL., CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Paper presented: Physiques en Herbe 92, Marseille (FR), July 5-10, 1992
Availability: Text not available
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