The effect of a radial electric field on ripple-trapped ions observed by neutral particle fluxes

The effect of a radial electric field on nonthermal ripple-trapped ions is investigated using toroidal Monte Carlo simulations for edge tokamak plasmas. The increase in the neutral particle flux from the ions trapped in local magnetic wells observed by the charge exchange (CX) detector at a low confinement to high confinement transition at ASDEX (Axially Symmetric Divertor Experiment). Upgrade tokamak [Proceedings of the 20th European Conference on Controlled Fusion and Plasma Physics, Lisbon (European Physical Society, Petit-Lancy, Switzerland, 1993), Vol. 17C, Part I, p. 267] is reproduced in the simulations by turning on a radial electric field near the plasma periphery. The poloidal and toroidal angles at which the CX detector signal is most sensitive to the radial electric field are determined. A fast response time of the signal in the range of 50-100 mu s to the appearance of the electric field can be found in the simulations with a relatively large half-width of the negative electric field region. (C) 1997 American Institute of Physics.