Spatially Resolved Measurements of Fully Ionized Low-ZImpurities in the PDX Tokamak

Fully ionized oxygen and carbon in PDX plasmas are detected via charge-exchange recombination reactions between the impurities and hydrogen atoms from a low-power neutral beam. The ${\mathrm{C}}^{6+}$ and ${\mathrm{O}}^{8+}$ ions are observed out to radii beyond the limiter, which is in contrast to expectations based on coronal equilibrium but consistent with a simple diffusive transport model. Central values of $Z_{\mathrm{eff}}$ obtained with these measurements agree with values obtained from plasma resistivity and visible bremsstrahlung measurements.