Z sub eff measurements in ATF using visible bremsstrahlung

Measurements of the effective charge Z{sub eff} in plasmas with electron cyclotron heating (ECH) and neutral beam injection (NBI) in the Advanced Toroidal Facility (ATF) have been carried out using visible bremsstrahlung. The electron temperature needed for the analysis is calculated from the measured stored energy and electron density. The value of Z{sub eff} varies widely depending on experimental conditions. In ECH plasmas it is between 2 and 8. In NBI plasmas, which are subject to radiation collapse, Z{sub eff} is between 3 and 5 at the time the stored energy reaches a maximum. However, Z{sub eff} is less than 2.5 in quasi-steady medium-density plasmas and is close to 1.2 in the highest-density plasmas, where the average electron density {bar n}{sub e} is of the order of 10{sup 14} cm{sup {minus}3}. 12 refs., 29 figs., 1 tab.