L. Moser – FuseNet PhD Event 2015 – Prague Influence of high magnetic field on plasma sputtering of ITER First Mirrors L. Moser, L. Marot, R. Steiner and E. Meyer Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland S. Alberti and I. Furno EPFL-SPC, Association Euratom-Confédération Suisse, CH-1015 Lausanne Switzerland F. Leipold and R. Reichle ITER Organization, Route de Vinon-sur-Verdon, St Paul-lez-Durance, France Service Contract ITER/CT/14/

L. Moser – FuseNet PhD Event 2015 – Prague International Thermonuclear Experimental Reactor (ITER) “The way to energy” Motivation Human size Why is the cleaning of ITER First Mirrors necessary?

L. Moser – FuseNet PhD Event 2015 – Prague ITER: About 40 diagnostics have to rely on mirrors. ITER I/O expects that 30 diagnostics will require mirror cleaning system. ITER Diagnostic subsystemsLIDAR: Plasma density and temperature Motivation

L. Moser – FuseNet PhD Event 2015 – Prague Erosion and deposition are the two main effects affecting the first mirrors reflectivity. The mirrors will be made of molybdenum or rhodium. [2] [1] [1]: D. Ivanova et al., An overview of the comprehensive First Mirror Test in JET with ITER-like wall, Physica Scripta, T159, (2014), [2]: G. De Temmerman et al., Journal of Applied Physics 102 (2007) 8 Motivation [1]

L. Moser – FuseNet PhD Event 2015 – Prague Radio-Frequency Plasma Cleaning Mirror During RF plasma, the target collects electrons and ions, avoiding any charging. A negative DC self-bias will be developed on the target. How is the cleaning performed?

L. Moser – FuseNet PhD Event 2015 – Prague Cleaning of Ø 25mm Mo mirrors : - Removal of Al/Al 2 O 3 - Al 2 O 3 - Al/Al 2 O 3 /W - W coatings with RF excitation with Ar (150 to 260eV) is successful. - In the presence of a magnetic field (0.35 T) an homogeneous removal of Al 2 O 3 film using RF excitation with Ar (200 eV) was achieved. The angle between the mirrors surface and the field lines was varied from 90 to 0°. Plasma cleaning with and without magnetic field Details: L. Moser et al., Nucl. Fusion 55 (2015) (9pp) L. Moser et al., J. Nucl. Mater. 463 (2015) pages 940–943 Cleaning of 200  300 mm 2 Mo mirrors : Removal of Al 2 O 3 film with RF excitation with Ar (200 eV) is successful and homogenous. Details: L. Moser et al., 27 th ITPA ITER, France Is the RF plasma cleaning working without magnetic field?

L. Moser – FuseNet PhD Event 2015 – Prague Magnet of gyrotron Several orientations between the mirror surface and the field. Plasma cleaning in a 3.5 T magnetic field 140mm Ø 50 mm

L. Moser – FuseNet PhD Event 2015 – Prague First cleaning results: Three Ø 18 mm SS polished mirrors (coated with 300nm NcMo) were coated with 10, 25 and 50 nm of Al 2 O 3. The cleaning was done at 1.2E-2mbar (argon) with -200V bias and 3.5 T magnetic field during 5h. The samples were fully (10 nm) or partially (25 and 50 nm) cleaned. The reflectivity was partially restored.  To fully clean the next samples, the time is increased from 5h to 7h and the Al 2 O 3 film is set to 25 nm. Cleaning in magnetic field: 90°, 3.5 T, -200V SS NcMo (300nm) Al 2 O 3 mirror B field α = 90°

L. Moser – FuseNet PhD Event 2015 – Prague The influence of the orientation of the magnetic field for cleaning at 0° was investigated and showed that this position is very sensitive for cleaning. mirror B field α = 90° Plasma cleaning in a 3.5 T magnetic field SS NcMo (300nm) Al 2 O 3 (25nm) mirror B field α = 0° -

L. Moser – FuseNet PhD Event 2015 – Prague One Ø 18 mm mirrors with 25 nm of Al 2 O 3. Cleaning at 45° with 3.5 Tesla and -200V bias (13W). Ar and 1.2E-2 mbar. The cleaning lasted 7h. Filamentation was observed during the plasma cleaning No pattern observed after cleaning on the mirror. Only the electrode had a small shadowed area CRPP_8 B field Cu Cleaning in magnetic field: 45°, 3.5 T, -200V mirror B field α = 45°

L. Moser – FuseNet PhD Event 2015 – Prague After 7h cleaning, the Al was fully removed and the Mo film was still present. XPS: No Al, only Mo Cleaning in magnetic field: 45°, 3.5 T, -200V

L. Moser – FuseNet PhD Event 2015 – Prague Cleaning at 30°Cleaning at 15°Cleaning at 0° (-85V) SS substrate after cleaning Reminder: for 45°, Mo still present. Cleaning in magnetic field: 7h plasma at 3.5 T, -200 V SS NcMo (300nm) Al 2 O 3 (25 nm)

L. Moser – FuseNet PhD Event 2015 – Prague One Ø 50 mm Cu polished electrode was coated with 25 nm of Al 2 O 3. Cleaning at 15° with 3.5 Tesla and -200V bias (18W). Ar and 1.2E-2 mbar. The cleaning lasted 1h. No filamentation was observed during the plasma cleaning B field A cleaning pattern was clearly observed on the electrode. Before After Cleaning in magnetic field: 15°, 3.5T, -200V, Big Mirror EDX measurements showed that the centre was fully cleaned. The pattern corresponds to region where the cleaning was not working. Cu Al 2 O 3 (25 nm)

L. Moser – FuseNet PhD Event 2015 – Prague Exp. 1: 0°, magnetic field Up (normal), problem with self-bias. Exp. 2: 0°, magnetic field Down (inverse), self-bias linear to RF power. Exp. 3: Exact same angle as for Exp. 2, field Up (normal), self-bias linear to RF power. Test at 0° ; 3.5 T (field inversion)

L. Moser – FuseNet PhD Event 2015 – Prague Three Cu insets in the electrode. Electrode polished before experiment. Ar and 1.2E-2 mbar. Electrode parallel to the B field. Cleaning for 2h30 (to see possible pattern on the electrode). B field 36W, 85V When the self-bias is difficult to reach (Exp. 1), large redeposition pattern can be observed in both direction (with inversion of the pattern). B field 36W, 100V When the self-bias is not difficult to reach (Exp. 2/3), no cleaning patterns are observed. The position at 0° is very sensitive to achieve a desired self-bias. 7h 2h30 Test at 0° ; 3.5 T (field inversion) 36W, 86V

L. Moser – FuseNet PhD Event 2015 – Prague 15°, B 15°, -B B field REDEPOSITION Old Design Angle between electrode and shielding: 15° New Design Angle between electrode and shielding: 0° d = 1.5 mm Outlook: New design

L. Moser – FuseNet PhD Event 2015 – Prague Outlook: Face to Face Cleaning 1 2 Two different configurations for investigation of various angles between electrode and magnetic field lines.

L. Moser – FuseNet PhD Event 2015 – Prague Conclusions For cleaning in magnetic field, the possibility to ignite the plasma (Ar and He) at 3.5 T and to perform sputtering of the Al 2 O 3 film was demonstrated for various angle. The sputtering properties are strongly dependant to the angle and the magnetic field intensity. Sputtering is much faster with a strong magnetic field and tangential angle. Questions?

L. Moser – FuseNet PhD Event 2015 – Prague Extra Slides

L. Moser – FuseNet PhD Event 2015 – Prague B field X Y A B C D EDX: Al Vs Cu A: 24.2 % B: 23.9 % C: 11.8 % D: 0.6 % Not zero in the centre but XPS measurements revealed no more Al, only Cu. Cleaning in magnetic field: 15°, 3.5 T, 200V, Big Mirror

L. Moser – FuseNet PhD Event 2015 – Prague B field Test at 0° ; 3.5 T (field inversion) E field Drift E field Drift

L. Moser – FuseNet PhD Event 2015 – Prague Reserve slide

L. Moser – FuseNet PhD Event 2015 – Prague Reserve slide L. Moser et al., Nucl. Fusion 55 (2015) (9pp)