Study of impurity transport in ohmically and neutral beam heated divertor discharges in JT-60

Abstract

The impurity transport characteristics of ohmically and neutral beam heated diverted plasmas in JT-60 have been studied. In sawtoothfree, ohmically heated plasmas with Ip = 1.5 MA, n̄e = (2−3) × 1019 m−3, q(a) = 3.2, no radiation buildup is observed. The temporal evolution of injected titanium has been measured by VUV and X-ray crystal spectrometers and PIN diodes. The spectral lines of Ti XX (259.3 Å) and Ti XXI (2.6097 Å) are compared with one-dimensional diffusive/convective impurity transport calculations. The transport calculations for Ohmic discharges with Ip = 1.5−2 MA, n̄e = (1–3) × 1019 m–3, q(a) = 3−3.7, show that DA =(1−2) m2⋅s−1 and that the inward convective velocity is small. In neutral beam heated plasmas with Ip = 1.5 MA, n̄e = 4 × 1019 m–3, q(a)= 3.6, Pb = 8 MW, no difference is observed in the global time evolution of the Ti XXI line emissions between co- and counter-injected discharges. The experimental observations are well represented by choosing DA = (1–2) m2⋅s−1 and a small inward velocity.