Sticking coefficient and SIMS of hydrocarbons on fusion relevant plasma-sprayed tungsten surfaces

Abstract

In this work we concentrate on the quantification of the sticking coefficient of CD3+ on fusion relevant plasma-sprayed tungsten (PSW) surfaces in the collision energy range from about 0 up to 100eV. PSW samples were cut from ASDEX Upgrade tiles and both untreated and electropolished surfaces are investigated. A collision energy, Ecoll, selected CD3+ ion beam deposits hydrocarbon layers onto the target surfaces which are ex-situ analyzed by nuclear reaction analysis (NRA) via D(3He,p)4He at 800kV and 2.5MeV, respectively. The sticking coefficient, S, for deuterium has been found to be collision energy dependent, decreasing with increasing energy. It is in the order of S∼0.4 for PSW and S∼0.1 for electro polished PSW at Ecoll=10eV. Secondary ion mass spectra of charged particles are recorded after ion–surface collisions with the polished PSW surface for collision energies up to 100eV. While at very low collision energies below about 10eV only simple reflection of CD3+ is observed, at higher collision energies both fragmentation of the projectile and fragmentation of ion–surface reaction products are observed. Concerning the stability of the layers we prove that hydrogen exchange plays a role on the time scale of weeks.