Shielding of a Tungsten Target From Impact of a Powerful Hydrogen Plasma Flow by Means of a Nitrogen Gas Screen

Shielding of materials from the impact of powerful plasma flows is of undoubted interest for solving a wide range of fundamental and applied problems. For example, to protect the divertor from the effects of high-temperature plasma during current interruptions in tokamaks, nitrogen or neon gas injection is used directly in front of the surface of the divertor plates. Also, using a gas screen, it is possible to regulate the thermal load on materials when they are irradiated with powerful plasma flows in order to improve the performance characteristics of surface layers. The work investigated the influence of a nitrogen gas screen on the shielding of tungsten when exposed to powerful flows of hydrogen plasma and on the localization of tungsten vapor near the surface of the irradiated target. It has been established that a gas screen of nitrogen with an atomic density of 2 × 1017 cm–3 in front of a tungsten target reduces the thermal load on the target by 2‒2.5 times less than the maximum level of energy absorbed by tungsten under pulsed action of a powerful flow of hydrogen plasma without a gas screen. The dependence of the density of energy absorbed by the target on the density of particles in the screen was experimentally determined. It is shown that, under our experimental conditions, the presence of a nitrogen gas screen in front of the target prevents the propagation of tungsten over distances of more than 1 cm along the magnetic field lines toward the incident plasma flow.