Secondary Electron Yield of Graphite and TiC Coatings

Transmission of microwave radiation at the lower hybrid frequency may induce multipactor breakdown in the coupling structure of a tokamak machine. To increase the R.F. power throughput to a plasma, secondary electron emission on the waveguide walls and subsequent electron multiplication which cause multipactor breakdown effect must be reduced. In this work measurements of secondary electron yields δ of two kinds of coatings (graphite, TiC) on S.S. were performed as a function of primary beam energies (100 eV; 1.1 keV). Also uncoated stainless steel was measured. Results show δ to have a typical energy dependence, with a peak occuring at 200 to 300 eV for normal electron beam incidence. The graphite and TiC coatings after surface treatment give δ_max < 1, which allows to reduce multipacting in waveguide.