Study of negative ion surface production in caesium-free H 2 plasma PhD student: Kostiantyn Achkasov...

Study of negative ion surface production in caesium-free H2 plasma

PhD student:• Kostiantyn Achkasov

Tutors:• Gilles Cartry and Alain Simonin

3rd FUSENET PhD Eventin Fusion Science and Engineering

University of York, 23rd - 26th of July 2013

2

Fundamentals

3rd FUSENET PhD Event in York: 26th of June 2013

Controlled thermonuclear fusion is one of the most promising future energy sources

3

Fundamentals



4

Fundamentals

ITER is the world's largest experimental tokamak nuclear fusion reactor being built at the south of France



5

Fundamentals


Required electron temperature: 10 – 20 keV (~108 °C)

only 1 keV can be achieved with Ohmic heating



6

Fundamentals


Required electron temperature: 10 – 20 keV (~108 °C)

only 1 keV can be achieved with Ohmic heating


one needs additional heating methods!3rd FUSENET PhD Event in York: 26th of June 2013

7

NBI for ITERNBI - neutral beam injection


5.3 m

4.7 m

15 m

8

NBI for ITER

17 MW &1 MeV of neutrals

Total weight > 900 tons

Calorimeter

Bushing

RID Neutralizer Ion source and accelerator

NBI - neutral beam injection


9

Why to use i- ?

neutrals of 1 MeV are needed to heat the ITER plasma core and ignite the fusion reactions


10


At such an energy:D+ → 0%D- → 56% of neutralisation efficiency

Ion neutralization

Why to use i- ?

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000

Energy of D+ or D- (keV)

Fra

ctio

n (

%)

D-

D+


11

Ion neutralization

Necessary D- current: ~ 50 A (250 A∙m-2)

Why to use i- ?

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000


Fra

ctio

n (

%)

D-

D+




0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000


Fra

ctio

n (

%)

D-

D+

12

new large i- source has to be developed!

Ion neutralization

Necessary D- current: ~ 50 A (250 A∙m-2)

Why to use i- ?




Present i– source

13

i- source conceptRF Driver


• i- surface production with Cs deposition

• has many drawbacks like diffusion of Cs inside the accelerator

• is presently the only way to meet ITER requirements

14

RF Driver

Present i– sourcei- source concept


Alternative solutions to the use of Cswould be highly valuable for the future fusion i- sources!

15

Present i– source

RF Driver• i- surface production with Cs deposition

• has many drawbacks like diffusion of Cs inside the accelerator

• is presently the only way to meet ITER requirements

i- source concept


16

Helicon reactor PHISIS

• H2 and D2 plasma

• P = 20 – 900 W• no magnetic field• preactor = 0.2 – 2 Pa

• capacitively coupled plasma mode

Experimental set-up

Graphite samplePump

Pyrex tube

Antenna

Coils

Mass Spectrometer Hiden EQP 300


17

Experimental set-up

Helicon reactor PHISIS

• H2 and D2 plasma

• P = 20 – 900 W• no magnetic field• preactor = 0.2 – 2 Pa

• capacitively coupled plasma mode


18

Langmuir probe

Sample

Experimental set-up

Mass Spectrometer


19

Measurement principle

VMS Vs Vp

Mass Spectrometer Plasma Sample

E

0


VMS Vs Vp

Mass Spectrometer Plasma Sample

20

E

0 10 20 30 40 50 60 70 80

0.01

0.1

1 0.2 Pa H2,100 W,V

p=21V

Vs=-130V D=37mm,

H2

+90%, HOPG, WS

H- c

ou

nts

/s

Energy (eV)

0

Negative ion distribution function (NIDF)

Measurement principle


0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)1 Pa H2,60 W, V

p=7V,V

s=-95V

21

Modeling of the NIDF


0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)

f(E) SRIM1 Pa H

2,60 W, V

p=7V,V

s=-95V

22


SRIM: the stopping and range of ions in matter


0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)

f(E) SRIM1 Pa H

2,60 W, V

p=7V,V

s=-95V

23


×× Plasma transmissionNIDF of i- emitted by

the surface

Surface

Mass spectrometer transmission


0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)

f(E) SRIM1 Pa H

2,60 W, V

p=7V,V

s=-95V

24


SRIM


the surface

Surface



0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)

f(E) SRIM1 Pa H

2,60 W, V

p=7V,V

s=-95V

25


SRIM SIMION


the surface

Surface



0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)

f(E) SRIM f ''(E) modeling

1 Pa H2,60 W, V

p=7V,V

s=-95V

26

• good agreement between F’’(E) and Fmeasured(E)



0 10 20 300.01

0.1

1

Energy (eV)

no

rma

lis

ed

in

ten

sit

y (

arb

.u)

Fmeasured

(E)

f(E) SRIM f ''(E) modeling

1 Pa H2,60 W, V

p=7V,V

s=-95V

27

• good agreement between F’’(E) and Fmeasured(E)

• SRIM calculation: C-H layer with 30% of hydrogen on the surface



NIDF studyof different carbon materials

28

highly oriented pyrolitic graphite (HOPG)

-40 -20 0 20 40 60 80

10

100

1000

10000

100000

35 °C 200 °C 400 °C 782 °C

Vs= - 130 V

= 0°

Inte

nsity

(ar

b. u

nits

)

Energy (eV)

HOPG 50 eV


29

-10 0 10 20 30 40 50 60 70

0.01

0.1

1

35 °C

Vs= - 130 V

= 0°

Inte

nsity

(ar

b. u

nits

)

Energy (eV)

HOPG 50 eV




30

-10 0 10 20 30 40 50 60 70

0.01

0.1

1

35 °C

Vs= - 130 V

= 0°

Inte

nsity

(ar

b. u

nits

)

Energy (eV)

HOPG 50 eV

F”(E,θ)30% H




31

0

0.01

0.1

1

35 °C 200 °C

Vs= - 130 V

= 0°

Inte

nsity

(ar

b. u

nits

)

Energy (eV)

HOPG 50 eV

F”(E,θ)30% H




32

0

0.01

0.1

1

35 °C 200 °C

Vs= - 130 V

= 0°

Inte

nsity

(ar

b. u

nits

)

Energy (eV)

HOPG 50 eV

F”(E,θ)20% H

F”(E,θ)30% H




33

H coverageon HOPG decreases with temperature

0

0.01

0.1

1

35 °C 200 °C

Vs= - 130 V

= 0°

Inte

nsity

(ar

b. u

nits

)

Energy (eV)

HOPG 50 eV

F”(E,θ)20% H

F”(E,θ)30% H




34

yield comparison

0 100 200 300 400 500 600 700 800

10000

100000

1000000

Vs= - 130 V

= 0°

HOPG

Tot

al y

ield

(ar

b. u

nits

)

T,°C



35

yield comparison

0 100 200 300 400 500 600 700 800

10000

100000

1000000

Vs= - 130 V

= 0°

HOPG

Tot

al y

ield

(ar

b. u

nits

)

T,°C


-10 0 10 20 30 40 50

HOPG

H- c

ount

s/s

(arb

uni

ts)

Energy (eV)


36

yield comparison

0 100 200 300 400 500 600 700 800

10000

100000

1000000

Vs= - 130 V

= 0°

HOPG

Tot

al y

ield

(ar

b. u

nits

)

T,°C


% H


37

yield comparison

0 100 200 300 400 500 600 700 800

10000

100000

1000000

Vs= - 130 V

= 0°

HOPG BDD

Tot

al y

ield

(ar

b. u

nits

)

T,°C


% H % H

% H

Boron-doped diamond:

BDD


38

yield comparison

0 100 200 300 400 500 600 700 800

10000

100000

1000000

Vs= - 130 V

= 0°

HOPG BDD ID

Tot

al y

ield

(ar

b. u

nits

)

T,°C


% H

biasing problemsbelow 400°C

% H % H

% H

Intrinsic diamond: ID


0 100 200 300 400 500 600 700 800

10000

100000

1000000

Vs= - 130 V

= 0°

HOPG BDD ID

Tot

al y

ield

(ar

b. u

nits

)

T,°C

39

yield comparison

% H % H

% H

% H

Raman spectroscopy:

sp3/sp2 BDD

sp3/sp2 HOPG

biasing problemsbelow 400°C



40

sp3/sp2 phase ratio

J. Robertson, Materials Science and Engineering, R37 (2002)

Raman spectroscopy:

sp3/sp2 BDD

sp3/sp2 HOPG



HOPG gives the highest i- yield at Troom

ID gives the highest i- yield at elevated T: 500°C

Conclusions




proper use of MS diagnostic and modeling allows to determine H coverage on the sample surface

Conclusions





MS combined with Raman spectroscopy shows:

the phase ratio sp3/sp2 changes when increasing T which alters the H surface coverage and the i- yield

Conclusions





MS combined with Raman spectroscopy shows:

the phase ratio sp3/sp2 changes when increasing T which alters the H surface coverage and the i- yield

New materials with the optimal sp3/sp2 state have to be probed deeper understanding is crucial

Conclusions


Perspectives


Next steps

prove experimentally the H surface coverage change with T:• Infrared Spectroscopy• Temperature Programmed Desorption Spectroscopy

Perspectives


Next steps


try out new materials:• low work-function materials (Gd, Ba, ...)• large band-gap insulators (Si, GaAs,…)

Perspectives

47

Next steps


try out new materials:• low work-function materials (Gd, Ba, ...)• large band-gap insulators (Si, GaAs,…)


Final steps

Test the chosen material in a real negative ion source (Cybele) equipped with an extraction device and a particle accelerator (MANTIS) in CEA-Cadarache

The End

Thank you for your attention

and time!


Study of negative ion surface production in caesium-free H 2 plasma PhD student: Kostiantyn Achkasov...

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