A diagnostic neutral beam injector based on radiofrequency ion source has been developed at BINP, Novosibirsk for plasma diagnostics in magnetic fusion devices including magnetic mirrors with pulse duration up to several seconds, plasma density up to 1020 m-3 and plasma radius ~0.5m.
It was observed that properties of the ceramic plasma box considerably changed after several hours of integrated operational time. After that, the proton specie in the beam essentially decreases. Eventually the proton component of the beam decreases approximately by 10% (from 60% down to 50% by current). This problem can be resolved by protection of the ceramic wall by a Faraday shield. We investigated the shield, which was made of aluminium tube with longitudinal slits and with a diameter close to that of the inner ceramic wall of the plasma box.
This paper discusses the results of the beam composition measurements after installation of the Faraday shield.
