Local emission and core concentration of tungsten in TEXTOR-94 plasmas operated with tungsten test and poloidal limiters

The correlation between the local WI light emission from W limiters and the W quasi-continuum light emission from the core plasma measured by the XUV spectrometer was investigated in the TEXTOR-94 limiter tokamak. The W quasi-continuum light emission showed a linear dependence against the line spectrum emission from neutral W from the metallic test limiter immersed in neutral beam (NBI) heated plasmas. The surface of the poloidal limiter made of vacuum-plasma-spray coating of W (VPS-W) was covered by a carbon layer during the time it was kept in the shadow of graphite ALT-II limiter. As a result of the carbon coating, the contribution to the W quasi-continuum intensity by the poloidal limiter was smaller than that by the test limiter, despite the fact that the surface area of the poloidal limiter facing the plasma was about seven times larger than that of the test limiter.