ELECTRON THERMAL TRANSPORT IN A SCAN OF THE EFFECTIVE ION CHARGE IN THE RTP TOKAMAK

A transport analysis is reported of a series of discharges in the Rijn huizen Tokamak Project (RTP) tokamak, in which Z(eff) was varied by us ing mixtures of helium and neon as the filling gas. Z(eff) was scanned over the range 5.1 to 9.5. As a reference, pure deuterium plasmas wit h Z(eff) less than or similar to 2 were used. Only a very weak depende nce of chi(e) on Z(eff) is observed, both in ohmic and in ECH discharg es. The scaling of chi(e) with n(e) and Z(eff) is consistent with the scaling of the global tau(Ee), both showing an absence of scaling with Z(eff). Scaling with the collisionality shows chi(e) similar to nu(e) (0.4) in ohmic discharges. A comparison is made with the predictions of transport models. Some models correlate with either the ohmic or th e ECH data set. None of the tested models, however, predicts the obser ved Z(eff) dependence of chi(e) in both ohmic plasmas and during ECH, It is noted that the ohmic discharges are in the plateau regime, while the ECH discharges are largely in the banana regime.