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Plasma surface interactions - Operations

Aims and scientific program

  

The PSI-Operations group is responsible for construction and operation of the new linear plasma device Magnum-PSI. This device will operate in steady-state with a 3-T superconducting magnet with a 10-cm diameter plasma beam. For hydrogen plasmas, flux densities of ~1024 m-2s-1 should be reachable at low electron temperatures (<10 eV). Basic operation of the device will start in fall 2010. This includes operation of several techniques for plasma and surface diagnostics.

The research program of the group involves technical studies relevant for construction and operation of the device and for plasma diagnostics. In addition, hydrogenic retention in refractory metals exposed to high-flux plasmas is studied; this research line will include experiments with novel plasma-facing materials.

 

Personnel

 

Function

Name

E-mail

Group Leader

P.A. Zeijlmans van Emmichoven

P [dot] A [dot] Zeijlmans [in_the_middle] Rijnhuizen [dot] nl

Research Engineer

H.J. van der Meiden

H [dot] J [dot] vanderMeiden [in_the_middle] Rijnhuizen [dot] nl

Research Technicians 

P.H.M. Smeets

P [dot] H [dot] M [dot] Smeets [in_the_middle] Rijnhuizen [dot] nl

 

H.J.N. van Eck

H [dot] J [dot] N [dot] vanEck [in_the_middle] Rijnhuizen [dot] nl

 

S. Brons

S [dot] Brons [in_the_middle] Rijnhuizen [dot] nl

 

P.R. Prins

P [dot] R [dot] Prins [in_the_middle] Rijnhuizen [dot] nl

 

O.G. Kruyt

O [dot] G [dot] Kruyt [in_the_middle] Rijnhuizen [dot] nl

 

J. Scholten

J [dot] Scholten [in_the_middle] Rijnhuizen [dot] nl

 

R.S. Al

R [dot] S [dot] Al [in_the_middle] Rijnhuizen [dot] nl

 

A.R. Lof

A [dot] R [dot] Lof [in_the_middle] Rijnhuizen [dot] nl

 

T. Oyevaar

T [dot] Oyevaar [in_the_middle] Rijnhuizen [dot] nl

 

C.A.J. van der Geer

C [dot] A [dot] J [dot] vanderGeer [in_the_middle] Rijnhuizen [dot] nl

PhD Student

M.H.J. ’t Hoen

Hoen [in_the_middle] Rijnhuizen [dot] nl

 

Research Highlights

 

Hydrogenic retention in tungsten exposed to ITER divertor relevant plasma flux densities

To better understand the effect of high-flux plasmas on refractory metals, tungsten (W) targets were exposed to high density, low temperature deuterium plasmas in Pilot-PSI. This investigation measured the amount of plasma-implanted deuterium that was trapped and retained in the tungsten target for a range of plasma exposure times (4 – 160 s). The plasma conditions were similar to what is expected in the ITER divertor (ne ~ 1020 m-3, Te ~ 2 eV, heat load ~ MW∙m-2) and the W target surface temperature was ~1600 K at the center of the target and decreased to ~1000 K at the edges. Deuterium retention was measured locally in the first 3 µm of the surface by nuclear reaction analysis (NRA). A 2-D NRA scan of the surface revealed significantly higher retention at the cooler edges (6 mm off center, Tw ~ 1000 K) of the target as compared to the center of the target. This indicated that surface temperature was playing a dominant role in determining hydrogenic retention properties as compared to plasma flux density or plasma fluence. Thermal desorption spectroscopy (TDS) measured the global retained deuterium inventory in the exposed W targets. TDS analysis showed very low retained fractions (10-5-10-7 Dretained/Dincident) and overall D inventory (Dretained = 0.5-1.5 x 1016 D). TDS also revealed that polishing the surface of the target enhances retention by a factor of ~2 while annealing the target at 1300 K for 30 minutes has little effect on hydrogenic retention under these conditions. Both TDS analysis and NRA showed no clear dependence of retained D on incident plasma fluence possibly indicating the absence of plasma-driven trap production under these exposure conditions. These results indicate that when operating at surface temperatures of 1000-1600 K, the W strikepoints of the ITER divertor will not retain significant amounts of deuterium (or tritium) due to the bombardment of the surface by the high flux of low energy plasma hydrogenic ions.

 

The left graph shows the results from the 2-D NRA scan of the W target exposed to D plasma for a total of 80 s (~1022 D total fluence). This clearly shows a minimum in retention at the hot center of the target and the highest retention at the cooler edges. The low retention seen at some of the 8 mm off center locations may be a shadowing effect from the target clamping ring. The right graphs show a) the total retained fluence as a function of incident fluence integrated across the entire exposed surface, and b) the retained fraction as a function of total incident fluence. The steep decrease and then flattening of the retained fraction in b) may indicate saturation in the W target.

Read more in: G.M Wright et al., J. Nuc. Mat., accepted for publication

 

Recent publications

 

'Modeling and experiments on differential pumping in linear plasma generators operating at high gas flows', H.J.N. van Eck et al., Journal of Applied Physics 105 (2009) 063307

 

'Hydrogenic retention in tungsten exposed to ITER divertor relevant plasma flux densities', G.M. Wright et al., Journal of Nuclear Materials 390-391 (2009) 610