High speed massive matter injection in ultrahigh vacuum environment for magnetic fusion devices

Thermonuclear fusion devices operate with hydrogen plasma at temperatures in the range of 100 - 200 million K. Conversely, the plasma density is very low (10²⁰ particles/m³). In order to achieve this low density and a high purity of the plasma, the pressure in the plasma vessel must be below 10^-4 Pa. Efficient plasma fuelling without impairing the quality of the vacuum is therefore often done by injecting pellets composed of cryogenic hydrogen. These pellets are injected into the plasma at speeds of about 1000 m/s, allowing particle deposition in the plasma core without degrading the surrounding vacuum. Furthermore, fusion devices of the Tokamak type rely on a very high electrical current (several MA) within the plasma. This bares the risk that the plasma disrupts within milliseconds which can cause severe damage to the fusion device. Hence, these disruptions have to be mitigated which is done by injecting massive amounts of noble gas. High speed gas valves, that operate inside or outside of the vacuum vessel, hold large amounts of noble gas which is released completely into the vacuum vessel within milliseconds (typical flow rate 10⁵ Pam³/s), putting a serious load on the vacuum system.