Abstract
Erosion and re-deposition of plasma-facing components in tokamaks require the development of in-vessel optics protection and cleaning techniques. Front-end diagnostic optics in large-scale fusion machines like ITER must be cleaned by a technique adopted for the in-vessel environmental conditions. The technique based on plasma sputtering in low pressure capacitively coupled radio frequency (CCRF) discharge is considered for the removal of the deposited metal films during the maintenance periods, in scenarios with and without the strong external magnetic field of several tesla. The sputtering efficiency is strongly dependent on energy and angular distribution of ions impinging the treated surface. This paper presents a numerical study of magnetized He+ ion motion within a collisional radio-frequency (rf) sheath of CCRF discharge in a spatially uniform oblique magnetic field using one-dimensional three velocity coordinate Particle-In-Cell Monte-Carlo Collision simulations. The effect of the magnetic field of 1–2.5 T, inclined to the normal of the treated electrode surface at an angle of 0–85° on the ion energy and angular distribution functions, is analyzed. A criterion of the magnetic sheath formation within the rf sheath is formulated.
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