Experiments about carbon removal and codeposit inhibition J.A. Ferreira, F.L. Tabarés, W. Bohmeyer...

Experiments about carbon removal and codeposit inhibition

J.A. Ferreira, F.L. Tabarés, W. Bohmeyer and J.A. Ferreira, F.L. Tabarés, W. Bohmeyer and A. Markin, I. Tanarro, V. HerreroA. Markin, I. Tanarro, V. Herrero

Introduction

Tritium Retention

Problem

Removal of Codeposits

Prevent the codeposition

Different techniques for

removal (Thermooxidation, GD cleaning, laser

ablation, etc)

Remove CFC´s

Scavenger technique

ELM’s, plasma operation?

Efficiency? Availability?

Does it work in ITER?

Cleaning (Experiments carried out at CIEMAT)

Cleaning chamber QMS chamber

Carbon layers (~200nm) were produced using a

He/CH4 or a He/C2H4 mixture by DC glow

discharge

Films were monitored using laser interferometry ( =

670 nm)

Residual gas was sampled using a differential pumped

mass spectrometer

2d

n

Cleaning with N2 GD

Nitrogen-containing DC glow discharge plasmas have shown erosion rates ~ 3 nm/min

Lower reactivity than He/O2 plasmas (similar conditions 12 nm/min)

Time (s)

0 1000 2000 3000 4000 5000 60000

0.1

0

0.5

1

1.5

2 x 10-7

16 17 25 52

18 26 27

C2N2

C2H2

HCN

H2O

a

b

Does it depend on the chemical form?

Cleaning with NH3 GD

Time (s)

Par

tial p

ress

ure

(A

.U.)

0 200 400 600 800 1000 12000

1

x 10-4 4 17 16 2

LaserH2

He

NH3

Time (s)

Par

tial p

ress

ure

(A

.U.)

0 200 400 600 800 1000 12000

1

x 10-4

Time (s)

Par

tial p

ress

ure

(A

.U.)

0 200 400 600 800 1000 12000

1

x 10-4 4 17 16 2

LaserH2

He

NH3

Time (s)

Par

tial p

ress

ure

(A.U

.)

0 200 400 600 800 1000 12000

2

4

6

8x 10

-6

182827262552

HCN

Time (s)

Par

tial p

ress

ure

(A.U

.)

0 200 400 600 800 1000 12000

2

Time (s)

Par

tial p

ress

ure

(A.U

.)

0 200 400 600 800 1000 12000

2

4

6

8x 10

-6

182827262552

HCN

He: 18,80 sccm, NH3: 13,50 sccm (42%). 200 mA, 450V

Erosion rate: 16,68 nm/min

Main product: HCN

Minor products: C2H2, C2N2

Some hydrogen of the film is released as H2

High erosion rate comparable

Rate HCN/C2H2 = 4,7318th PSI (Toledo) J.A. Ferreira et al P1-53

3 2 2 2982NH N 3H 91,86 kJ/molH

Thermooxidation with NO2

18th PSI (Toledo) I. Tanarro et al P3-51

Left: Hard a-C:H film (~100 nm), deposited on a stainless steel sample.

Right: After 1 hour thermal oxidation with O2, 50 mbar, at 400ºC, the a-C:H film was nearly completely eliminated. In the case of NO2 / N2 (1:1), the films were completely eliminated even at 300ºC.

1 mm gap

Scavenger

18th PSI (Toledo) W. Bohmeyer et al O-15

What is it?gas phase reactions of nitrogen or nitrogen

containing species with the growth precursors. Formation of non-reactive species that can be pumped

away

CxHy NX+Stable non-

reactive species

F.L.Tabarés, V. Rohde and the AUG TeamNucl. Fusion 45 (2005) L27-L31.

Scavenger (PSI-2)

No uncontrolled CxHy losses at cold walls

The behavior of re-eroded species is studied

Ions can not reach the collector plates


Scavenger (PSI-2)


20.00 40.00 60.00 80.00 100.00 120.00distance to neutra lizer p late / cm

-0.40

0.00

0.40

0.80

depo

sitio

n n

m/m

in

2 sccm m ethane

0.5 sccm m ethane

no m ethane

QMS:CH4:C2H2:C2H6=3:4:2

High sticking species

Pump Duct Deposition Profile

Scavenger (PSI-2)


220 240 260 280 300 320 340 360time (min)

54

55

56

57

58

thi c

k nes

s(n

m)

2 sccm CH4

2 sccm N2

-0.044 nm/min

-0.044 nm/min

2 sccm N2

no injection

Tcoll =330 K

+0.031nm/min -0.043 nm/min

220 240 260 280 300 320 340 360time (min)

54

55

56

57

58

thi c

k nes

s(n

m)

2 sccm CH4

2 sccm N2

-0.044 nm/min

-0.044 nm/min

2 sccm N2

no injection

Tcoll =330 K

+0.031nm/min

220 240 260 280 300 320 340 360time (min)

54

55

56

57

58

thi c

k nes

s(n

m)

2 sccm CH4

2 sccm N2

-0.044 nm/min

-0.044 nm/min

2 sccm N2

no injection

Tcoll =330 K

+0.031nm/min -0.043 nm/min

Strong influence of nitrogen during methane injection

No influence of nitrogen for clean plasma (not enhanced erosion by nitrogen)

Scavenger effect: yes, it works !

Pump duct / nitrogen

Scavenger (PSI-2)


Pump duct: Collector temperature 310 and 330 K

0 5E+3 1E+4 2E+4 2E+4 3E+4 3E+4time / s

67

68

69

70

71

72

73

74

75

76

thic

knes

s/n

m

PLASMAON

310 K 330 K

2 sccm CH4

2 sccm N2

collector temperature:

0 5E+3 1E+4 2E+4 2E+4 3E+4 3E+4time / s

67

68

69

70

71

72

73

74

75

76

thic

knes

s/n

m

PLASMAON

310 K 330 K

2 sccm CH4

2 sccm N2


0 5E+3 1E+4 2E+4 2E+4 3E+4 3E+4time / s

67

68

69

70

71

72

73

74

75

76

thic

knes

s/n

m

PLASMAON

310 K 330 K

2 sccm CH4

2 sccm N2


Nitrogen effect:Reduction of

deposition (310 K)

Shift to from deposition to erosion (330 K)

Scavenger (PSI-2)


Pump duct : deposition profile

Ex situ thickness measurement

(Tcoll not fixed , about 320 K)

Strong influence of nitrogen

Scavenger (PSI-2)


0 5000 10000 15000Time (sec)

67

68

69

70

71

72

73

74

Pro

be th

ickn

ess

(nm

)

H plasma 150A

2 sccm CH4

N2to dump(sccm)

2 1 0,5

N2to nozzle(sccm)

0,5 0,2

0 5000 10000 15000Time (sec)

67

68

69

70

71

72

73

74

Pro

be th

ickn

ess

(nm

)

H plasma 150A

2 sccm CH4

N2to dump(sccm)

2 1 0,5

N2to nozzle(sccm)

0,5 0,2

0 5000 10000 15000Time (sec)

67

68

69

70

71

72

73

74

Pro

be th

ickn

ess

(nm

)

H plasma 150A

2 sccm CH4

N2to dump(sccm)

2 1 0,5

N2to nozzle(sccm)

0,5 0,2

1.Into the pump duct:

Weak effect

2.Into the hot tube:

Stronger effect

Nitrogen injection at

different positions

Scavenger (PSI-2)


Neon injection

Neon has no influence !

8000 12000 16000 20000 24000 28000 32000time / s

60

62

64

66

68

70

72

74

fi lm

thi c

knes

s / n

m

PlasmaON

PlasmaOFF

310 K 330 K 350 K

2 sccm CH4

1.4 sccm Ne


Scavenger (PSI-2)


vacuum chamber wall

Optical system:in-situ film thickness

He/H2/D2/Ar plasma

Si collector

Injection ofCH4/N2/H2

QMS

vacuum chamber wall

Optical system:in-situ film thickness

He/H2/D2/Ar plasma

Si collector

Injection ofCH4/N2/H2

QMS

Protection of the collector area

against ions by an additional limiter Ions are not included

in the deposition process

Main chamber experimental set-up

Scavenger (PSI-2)


Main chamber. He plasma

0 25 50 75 100 225 250 275

0

10

20

30

40

50

60

70

80

90

0

10

20

30

40

50

60

70

80

90

0 25 50 75 100 225 250 275

0

10

20

30

40

50

60

70

80

90

0

10

20

30

40

50

60

70

80

90

thic

knes

s [n

m]

time [min]

CH4 N2

0.5sccm0.5 sccm 1.0 sccm

0.220 nm/min

0.466

0.4820.527

No atomic hydrogen no HCN and NHx

Deposition is not influenced no volume process

No erosion no surface effect

Scavenger (PSI-2)


Main chamber. H2 discharge, methane, nitrogen

25 50 75 100 125 150

70

80

90

100

110

120

70

80

90

100

110

120

thic

knes

s [n

m]

time [min]

CH4

N2

-0.746

2.351 nm/min

-0.303

-1.630

0.115

0.999

-0.318

substrate: 330K

1 1 sccm1 sccm

I II III IV V VI VII

25 50 75 100 125 150

70

80

90

100

110

120

70

80

90

100

110

120

25 50 75 100 125 150

70

80

90

100

110

120

70

80

90

100

110

120

thic

knes

s [n

m]

time [min]

CH4

thic

knes

s [n

m]

time [min]

CH4

N2

-0.746

2.351 nm/min

-0.303

-1.630

0.115

0.999

-0.318

substrate: 330K

1 1 sccm1 sccm

I II III IV V VI VII

Enhanced erosion Surface

Reaction

Reduced depositionSurface and volume

process

Scavenger (PSI-2)


Nitrogen molecules are stable and don’t influence film formation, but they are decomposed in the plasma.

Close to the plasma (where energetic neutrals are included) enhanced erosion was detected (surface process) as well as a reduction of the deposition rate by a volume process

Far away from the plasma was detected only a volume effect, the conversion of (high sticking) hydrocarbons to inert ones, the so called scavenger effect. Enhanced erosion was not found.

Scavengers (CIEMAT)

Tiempo (s)

Pre

sió

n p

arc

ial (

U.A

.)

1000 1500 2000 2500 3000 3500 40000

0.2

0.4

0.6

0.8

1x 10-5

521618252627282930

Tiempo (s)

Pre

sión

par

cial

(U

.A.)

1500 2000 2500 3000 350010

-10

10-9

10-8

10-7

10-6

10-5

b)a) Residual gas analysis and CTAMS spectra

show a strong production of hydrocarbons (HCN/C2=0,1 C2H2/C2H4=3)

A second peak of acetylene is also observed. Could not be explain as temperature is too high for being acetylene (unstable species???)

Contribution of acetonitrile

Time (min)

Par

tial P

ress

ure

20 30 40 50 600

1

2

3

4x 10

-8

3940414243

Carbon walls

Scavengers (CIEMAT)

Scavenger mixtures (H2:N2:CH4) on metallic walls show a very different ratio of products (ammonia and acetonitrile are the main products!)

In our small set-up surface chemistry prevails

Pa

rtia

l Pre

ssu

re (

A.U

.)

200 400 600 8000

0.5

1

1.5x 10-5

16171825262728394041

Desorption of condensible products at liquid nitrogen

temperature (CTAMS)

Conclusions

Some alternatives based on nitrogen compounds could be of interest not only for tritium recovery (codeposition cleaning) but also for inhibition of the formation of codeposits

Experiments carried out in PSI-2 have shown that nitrogen containing mixtures are able to stop codeposition in hidden areas (not reached by ions)

Nitrogen reacts to form ammonia in hydrogen plasmas. Last results suggest that ammonia related molecules (NHx) could be responsible of scavenger effect

3 3 4 2CH NH CH NH ???? 3N+CH HCN+2H????

Experiments about carbon removal and codeposit inhibition J.A. Ferreira, F.L. Tabarés, W. Bohmeyer...

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Transcript of Experiments about carbon removal and codeposit inhibition J.A. Ferreira, F.L. Tabarés, W. Bohmeyer...