Erosion and retention of the target plate material in the ASDEX divertor

Abstract

In this paper we describe experiments undertaken to evaluate the retention of target produced impurities in the ASDEX divertor. The titanium divertor plates have recently been replaced by water-cooled copper plates. Since copper is a material not previously present inside the ASDEX torus, a unique possibility existed to study the transport of the target plate material from the divertor chamber into the main plasma. By spectroscopic measurement of the Cu flux emerging from the target plate and of the Cu density in the main plasma, the retention is assessed. We find a poor retention ( R = 1) for low n e ( n e < 3.0 × 10 13 cm −3) but a substantially improved one ( R > 30) at high densities. During additional heating (N1, ICRH) at the same density as in the OH case, the retention is lower, but approaches similar values at slightly higher densities. The retention seems to be independent of the heating power.