Dynamic behavior of plasma space potential in toroidal helical plasmas

Summary form only given. A heavy ion beam probe (HIBP) is a unique diagnostic which can measure plasma space potential with high spatial and temporal resolution. The radial electric field can be deduced from the potential profile. We have installed a 200 keV beam HIBP on the Compact Helical System (CHS). The fast time response of this diagnostic makes it possible to study fast phenomena such as transition, collapse and fluctuations as well as static space potential profiles. In this paper, recent experimental results from the CHS HIBP will be presented, with special emphasis on the dynamic behavior of the space potential associated with electric field bifurcation and on potential oscillations during bursting MHD instabilities. These results have produced new insights for plasmas confined by toroidal helical systems.