N. Ohyabu

T. Watanabe

T. Watari

Watanabe,  T.

Watari,  T.

Ohyabu,  N.

NIFS-Repository (National Institute for Fusion Science)

§32. Advanced Divertor Concept - RF Diver-tor Watanabe, T., Watari, T., Ohyabu, N. The design of divertor is one of the most diffi-cult problems of the fusion reactor systems. The roles of divertor are safe heat removal from core plasma region, particle control and improving of core plasma confinement. The application of radio-frequency (RF) forces to divertor plasma is proposed for the improve-ment of its relevance to reactors. RF fields are applied at the entrance of closed divertor rooms. Ponderomotive forces sustain high den-sity scrape-off plasma which screens the pene-tration of neutral atoms into core plasma re-gions, and create positive electrostatic potential in scrape-off plasma region which suppresses the penetration of impurity ions from divert or rooms. Ponderomotive force for electron is also applied to prevent the upstream flow of cold electrons from divertor rooms to scrape-off regions. We introduce simplified 1-D model for the LHD divertor as shown in Fig.1(b) to study the features of rf divertor plasma flow analyti-cally and numerically. As basic equations, we use the multi-fluid equations and Poisson equa- . (a) LHD Helical Divertor stagnation point (b) 1-D model R(m) baffle plate divertor plate tion. Time evolution of divertor plasma flow is neutralgas solved numerically with ponderomotive force ef- ~ir;=-·==--=~~~~~im~pun;·;,ty.JI-,. fects. Potential barrier to stop the upstream flow f! of impurity is sustained at entrance of divertor j '-room. Density of scrape-off plasma is also sus- 1 "" cold electron X • stagnation point tained in high level compared to the case of no 1 RF Plug rf fields. These results are summarized in [1]. 1 1 Reference 1) Watanabe,T., Watari, T. and Ohyabu, N., Fusion Engineering and Design, 26 (1995) 365. 0 2 4 6 x(m) Fig.l (a) Magnetic field configuration of LHD including divertor field lines. (b) 1-D model for divert or plasma flow. Coordinate x represents the distance from the stagnation point to divertor plate. Divertor plasma is as-sumed to be symmetric with the stagnation point (x == 0). 161 

Advanced Divertor Concept - RF Divertor

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