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

Abstract

Abstract:In this work we concentrate on the quantification of the sticking coefficient of CD 3 + on fusion relevant plasma-sprayed tungsten (PSW) surfaces in the collision energy range from about 0 up to 100 eV. PSW samples were cut from ASDEX Upgrade tiles and both untreated and electropolished surfaces are investigated. A collision energy, E coll , selected CD 3 + ion beam deposits hydrocarbon layers onto the target surfaces which are ex-situ analysed by Nuclear Reaction Analysis (NRA) via D( 3 He,p) 4 He at 800 kV and 2.5 MeV, 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 S0.1 for electro polished PSW at E coll = 10 eV. Secondary ion mass spectra of charged particles are recorded after ion-surface collisions with the polished PSW surface for collision energies up to 100 eV. While at very low collision energies below about 10 eV only simple reflection of CD 3 + 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.

Reflection properties of small hydrocarbons impinging on tungsten and carbon surfaces

“…As already mentioned, like in the previous experiment [7] the shape of the ion beam spot is found to be elliptical with an area of approximately 1 Â 1.5 mm 2 by determining the horizontal and vertical distribution function of the deuterium content around the spots exposed to the CD þ 2 beam with NRA using a 3 He beam of 1 Â 1 mm 2 size. By comparing the fluence with the areal density of deuterium, the sticking coefficient of deuterium is found not to show the same dependency on incident energy over the investigated energy range up to 100 eV.…”

“…Our first experiment concerning the question of fuel retention by deposition of hydrocarbon ions formed subsequently to impact of deuterium on carbon surfaces in an experimental fusion reactor cladded with vacuum plasma sprayed tungsten coated tiles, showed that electron-polishing of plasma-sprayed tungsten surfaces reduces the magnitude of the sticking coefficient of a hydrocarbon species known for its high adsorption probability, the methyl radical ion CD þ 3 by a factor of about 4 [7]. Our main aim was to quantify the sticking coefficients of the next smaller deuterated hydrocarbon CD þ 2 on untreated PSW and for comparison also on CFC surfaces.…”

Plasma-wall interaction: a complex combination of surface processes critical for thermo-nuclear fusion

“…At thermal energies the sticking coefficient depends strongly on the electronic configuration of the hydrocarbon molecules decreasing from sp1 to sp2 and sp3 in reasonable agreement with MD calculations, which predicting sticking coefficients close to 1 at energies above 10 eV. Data for sticking coefficients on realistic plasma-facing materials were presented recently [52] and are further studied in the framework of the EU PWI Task Force.…”

Plasma–wall interaction: Important ion induced surface processes and strategy of the EU Task Force

“…While without excitation decomposition of incident CH 4 + molecules starts only at 30 eV, indicating that the whole dissociation energy must be supplied by the surface collision, for high internal excitation sufficient to provide the decomposition energy of 1.8 eV the reemission of CH 4 + decreases monotonically with ion energy. Data for sticking coefficients on realistic plasma-facing materials were presented in this conference [61].…”