Damage to N-NBI systems due to positive ion back-streaming

2 Sep 2020, 06:40
20m
Oral Beam lines and facilities H– and D– sources for fusion: Oral session O1

Speaker

Prof. Motoi Wada (Doshisha University)

Description

Long term stability of a plasma heating system is indispensable for realizing a DEMO nuclear fusion reactor. One possible cause for deteriorating the accelerator/ion source system of negative ion based neutral beam injection (N-NBI) heating is the damage due to energetic positive ions back-streaming from the beam produced plasma. The positive ions strike the surfaces of downstream sides of the extraction/acceleration electrodes and they can acquire the full acceleration energy to bombard the back end-plate of the ion source. The heat flux should be comparable or even greater than that to divertor as the beam energy and the current density reach ITER design goals. The robustness against the damage due to back-streaming ions should now be evaluated by taking the reactor operation life into account.

Particle retention directly affects the collision cascade of a high energy particle injected into solid materials and the resulting sputtering yields. Local temperature of the solid retaining injected particles determines the diffusion of the retained particles, and thus can largely modify the overall erosion rate of the solid. The effects due to long term exposures to intense particle injections of deuterium are studied with the computer simulation code ACAT (Atomic Collision in Amorphous Target) for molybdenum: the candidate material of the back end-plate for an ion sources of a DEMO reactor.

Summary

Sputtering erosion by back streaming ions may become larger as the deuterium retention of the ion source/accelerator components increases.

Primary authors

Prof. Motoi Wada (Doshisha University) Prof. Takahiro Kenmotsu (Doshisha University ) katsunori ikeda (National Institute for Fusion Science) Masashi Kisaki (National Institute for Fusion Science) Haruhisa Nakano (National Institute for Fusion Science, National Institutes of Natural Sciences) Katsuyoshi Tsumori (National Institute for Fusion Science)

Presentation Materials

Peer reviewing

Paper