Study of co-deposited carbon layers and of mixed (W+C) layers on tungsten and graphite in a plasma accelerator

In the present work samples of W and graphite were exposed in the C2H2 plasma for modelling the co-deposition process in a tokomak divertor. The energy of C2H2 ions, bombarding the surface was 300eV. This means that the H+-ion energy was lower than the threshold energy for W and C sputtering. Carbon co-deposited layers with globular structure similar to that obtained in tokamaks on W and C were produced. The structure of co-deposited films on W varied from uniformly smooth under low irradiation doses (⩽1×1023m−2) to a globular one under high doses (1024m−2). Films with a globular structure appear on graphite already at a dose of 2×1023m−2. The globular film production occurs by the appearance of separate small globules and by a gradual increase in their density and size. The film density is equal to 0.52 and 0.79 of that for crystalline graphite for the homogeneous structure and for the globular one, respectively. The integral H content in the co-deposited films is reduced with an increase in the globular structure fraction on the W surface from 7.2×1021 to 3.2×1021m−2 for a dose increase from 1×1023 to 1×1024m−2. Under simultaneous irradiation of W and C by C2H2 ions mixed (W+C) layers, 500nm thick, were produced on W and C surfaces. The integral hydrogen content in the (W+C) film on graphite is 2.3 times higher than the H content in the mixed layer on W.