Heat and Particle Control of High-Temperature Plasmas

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A toroidal belt limiter with a pumping system have been utilize to control heat and particle fluxes from high temperature plasmas in TEXTOR.It has been confirmedwith particle balance analysis that hydrogen recycling at the wall is reduced just after the pellet injection and after helium injection.High Z test limiter experiments indicated that tungsten or molybdenum accumulation occasionally takes place in L mode discharges.But it causes a deleterious effect on plasma performance in only limited cases such as in high density, ohmically heated operation etc.Observed short range in sputterd neutral Mo atoms indicates prompt redeposition of Moions.This results in low erosion rate of the surface and little penetration of impurity atoms into plasma boundary.RF biasing to a limiter head reduced density and particle flux to the limter head.However, reduction of het flux has not yet been verified in spite of an expectation from based on a theoretical consideration.Through this collaboration study, some of beneficial effects have been confirmed experimentaly for pump-limiter combined with pellet fuelling, high Z limiter materials, RF biasing to the limiter head, as is above noted.Among the results above noted, the high Z limiter study attracts a lot of worldwide interests in these days.Many new programs of high Z study have been started in several tokamaks under direct influence of this TEXTOR collaboration.In TEXTOR,a design of an advanced limiter system is stated based on the results above noted.