He++Transport in the PDX Tokamak

A powerful new approach to the study of particle transport and helium ash confinement in high-temperature fusion plasmas is demonstrated by charge-exchange recombination spectroscopy of ${\mathrm{He}}^{++}$ in Ohmically heated PDX discharges. Time- and space-resolved measurements of ${\mathrm{He}}^{++}$ density following a short puff of helium gas into the plasma edge are fitted with use of a diffusive/convective transport model with coefficients $D=(2.1\mathrm{}\pm 0.9)\times {10}^4$ ${\mathrm{cm}}^2$ ${\mathrm{s}}^{-1\mathrm{}}$ and $\frac{v\left(r\right)\mathrm{}}{D}=\frac{(0.8\mathrm{}\pm 0.3)\partial \left(\ln n_e\right)}{\partial r}$.