1 Deuterium retention and release in tungsten co- deposited layers G. De Temmerman a,b, and R.P. Doerner a a Center for Energy Research, University of California at San Diego, USA b Present address: EURATOM/UKAEA Fusion Association, Culham Science Centre, UK G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain

2 Motivation  Co-deposition of material eroded from PFCs (C,Be,W) with tritium will contribute to the global tritium retention in ITER  Deuterium retention in Be co-deposited layers depends on Be deposition rate, energy of D particles and substrate temperature [1]  Although the erosion rate of tungsten will be much lower than that of Be/C, knowledge of the possible retention in codeposited W layers is required  Also, thermal release behaviour of hydrogen isotopes needs to be studied to determine the efficiency of fuel removal methods G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain 1 G. De Temmerman, Nucl. Fusion, in press

3 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain Ar +,D W Atomss Copper substrate Tungsten target  Tungsten layers formed by DC-magnetron sputtering using a tungsten target  D 2 /Ar mixtures Experimental (1/2) DC power supply, -400V on target W target T substrate =RT-300C P=20mTorr Copper substrate Deposition rate: QMB+weight measurement Retention: TDS Morphology: SEM

4 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain Cu substrate B field W target ion flux: ·10 22 m 2 s -1 T e ~ 6 eV target bias –50/-150 V T target ~ 600°C Copper substrate  PISCES-B is a linear plasma device  Steady state plasma generated by an arc discharge initiated by a heated LaB 6 cathode Deposition rate Retention: TDS Morphology: SEM Experimental (2/2)

5 Influence of the substrate temperature during deposition  Layers prepared with different substrate temperatures (15% Ar)  Layer thickness: nm (magnetron), nm (PISCES-B) D/W decreases with increasing substrate temperature D/W  0.03 at room temperature G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain

6 Influence of the tungsten deposition rate (1/3)  2 ways of varying the deposition rate: 1.Vary the power to the magnetron (mainly change current to target, not voltage) Factor of 2 increase of deposition rate for 4 times the power No clear effect on the retention RT

 2 ways of varying the deposition rate: 2.Vary the Ar fraction in the gas mixture Influence of the tungsten deposition rate (2/3) 2 orders of magnitude variation of deposition rate Decrease of the retention with increasing deposition rate RT 7 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain

8 Influence of the tungsten deposition rate (3/3)  If we assume that the Ar fraction only affects the deposition rate (flux of D to the surface higher than flux of W) General trend is a decrease of D retention for increasing deposition rate

9 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain Combined effect of deposition conditions  Regression analysis of the data Retention in co-deposited tungsten layers depends on the energy of the incident D particles, the W deposition rate and substrate temperature  For beryllium:

10 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain Layer morphology 15% Ar, RT 5% Ar, RT 5% Ar, RT, 45deg tilt  Dense and smooth layer formed with 15% Ar  At lower Ar concentration, formation of blister-like structures  large size distribution

 TDS measurements made with thermocouple against the sample back Deuterium thermal desorption 2 distinct desorption stages at 200C and 800C 11 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain

Desorption kinetics  Comparison of the desorption kinetics of co-deposited W and Be layers  Temperature ramped up to 250C and then held for a given time For Be: desorption stops at target temperature and restarts when temperature is ramped again For W: exponential fall of desorption rate: diffusion limited process 12 G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain W Be

 Retention in co-deposited tungsten layers generally pretty low  D/W=0.15 has been measured for very low deposition rate (implantation of D in the layer ?). Similar observations in [2]  Retention decreases with increasing deposition rate and temperature  Retention increases with energy of the incident particles  Variation with deposition conditions similar to what is observed for Be  Deuterium desorption is a diffusion limited process: duration of the bakeout is important Conclusions 2 K. Katayama, et al, Fus. Eng. Des., 82 (2007) G. De Temmerman9 th Int. workshop on H isotopes in FRM, June , Salamanca, Spain