l. moser – fusenet phd event 2015 – prague influence of high magnetic field on plasma sputtering...

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. MeyerDepartment 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. ReichleITER Organization, Route de Vinon-sur-Verdon, 13115 St Paul-lez-Durance, France

Service Contract ITER/CT/14/4300000953


International Thermonuclear Experimental Reactor (ITER)“The way to energy”

Motivation

Human size


ITER: About 40 diagnostics have to rely on mirrors.

ITER I/O expects that 30 diagnostics will require mirror cleaning system.

ITER Diagnostic subsystems LIDAR: Plasma density and temperature

Motivation

Moser Lucas

35 diagnostics uses mirrors, for a total of 80 mirrorsExpliquer pourquoi on a des mirroirs et pas juste des fenêtres.


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), 014011[2]: G. De Temmerman et al., Journal of Applied Physics 102 (2007) 8

Motivation

[1]

Moser Lucas

Dire pk Al et pas Be


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.


Cleaning of Ø 25mm Mo mirrors :

- Removal of Al/Al2O3 - Al2O3 - Al/Al2O3/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 Al2O3 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) 063020 (9pp) L. Moser et al., J. Nucl. Mater. 463 (2015) pages 940–943

Cleaning of 200300 mm2 Mo mirrors :

Removal of Al2O3 film with RF excitation with Ar (200 eV) is successful and homogenous.

Details: L. Moser et al., 27th ITPA ITER, France


Magnet of gyrotron

Several orientations between the

mirror surface and the field.

Plasma cleaning in a 3.5 T magnetic field

-200

-100

0100

200

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Field (T)

Po

sit

ion

z (

mm

)

Top flange position

140mm

Ø 50 mm


First cleaning results:

Three Ø 18 mm SS polished mirrors (coated with 300nm NcMo) were coated with

10, 25 and 50 nm of Al2O3. 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 Al2O3

film is set to 25 nm.

Cleaning in magnetic field: 90°, 3.5 T, -200V

SSNcMo (300nm)

Al2O3

mirror

B field

α = 90°


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

SSNcMo (300nm)Al2O3 (25nm)

mirror B field

α = 0°

Bias Angle Field Time Comments Result

90° 5h 10, 25, and 50nm Al2O3

Al film partially gone

45° Al film gone

30°Mo film

partially gone15° Mo film gone0° Mo film gone

15° Big Cu 1hAl film gone except edges

7h3.5 T200 V

Cleaning (Al2O3)

25nm Al2O3

-


One Ø 18 mm mirrors with 25 nm of Al2O3.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

Cu


mirror

B field

α = 45°


After 7h cleaning, the Al was fully removed and the Mo film was still present.XPS: No Al, only Mo


500 1000 1500 2000 250002

15

30

45

60

75

90

Specular NcMo Diffuse NcMo Specular after cleaning Diffuse after cleaning Specular Al

2O

3

Ref

lect

ivit

y (%

)

Wavelength (nm)

CRPP_8


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

SSNcMo (300nm)Al2O3 (25 nm)

500 1000 1500 2000 25000

10

20

30

40

Cleaning at 0° Cleaning at 15° Cleaning at 30°

Dif

fuse

ref

lect

ivit

y (%

)

Wavelength (nm)


One Ø 50 mm Cu polished electrode was coated with 25 nm of Al2O3.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.

CuAl2O3 (25 nm)


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.

0 50 100 150 200 250 3000

50

100

150

200

250

300

350

Sel

f-bi

as (

V)

Power (W)

Exp. 1 Exp. 2 Exp. 3

Test at 0° ; 3.5 T (field inversion)


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

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

2h30


0 50 100 150 200 250 3000

50

100

150

200

250

300

350

Sel

f-bi

as (

V)

Power (W)

Exp. 1 Exp. 2 Exp. 3

36W, 86V


15°, B

15°, -B

B field

B field

REDEPOSITION

Old DesignAngle between electrode and shielding: 15°

New DesignAngle between electrode and shielding: 0°

d = 1.5 mm

Outlook: New design


Outlook: Face to Face Cleaning

1

2

Two different configurations for investigation of various angles

between electrode and magnetic field

lines.


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 Al2O3 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?


Extra Slides


B field

XY

0 10 20 30 40 500

4

8

12

16

20

Y (mm)

ED

X:

Al V

s C

u (

%)

Before cleaning After cleaning

A

B C

D

EDX: Al Vs CuA: 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.

0 10 20 30 40 500

4

8

12

16

20

24

X (mm)

ED

X:

Al V

s C

u (

%)

Before cleaning After cleaning

Cleaning in magnetic field: 15°, 3.5 T, 200V, Big Mirror


B field

B field


E field

Drift

E field

Drift


Reserve slide


Reserve slide

L. Moser et al., Nucl. Fusion 55 (2015) 063020 (9pp)

l. moser – fusenet phd event 2015 – prague influence of high magnetic field on plasma sputtering...

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