Measurement of the Plasma Driven Permeation Flux in the Spherical Tokamak QUEST

S. K. Sharma1

H. Zushi2, I. Takagi3, Y.Hisano1, M. Sakamoto2, Y. Higashizono2, T. Shikama3, S. Morita4, T. Tanabe1, N. Yoshida2, K. Hanada2, M. Hasegawa2, O. Mitarai5, K. Nakamura2, H. Idei2, K.

N. Sato2, S. Kawasaki2, H. Nakashima2, A. Higashijima2, Y. Nakashima6, N. Nishino7, Y.Hatano8, A. Sagara4, Y. Nakamura4, N. Ashikawa4, T. Maekawa3, Y. Kishimoto3, Y.

Takase9 and QUEST Group

1IGSES, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan2RIAM, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan

3Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University, Japan

4 National Institute for Fusion Science, Toki, Japan5Kyushu Tokai University, 9-1-1 Toroku, Kumamoto 862-8652, Japan

6Plasma Research Center, University of Tsukuba, Japan7Department of Mechanical System Engineering, Graduate School of Engineering,

Hiroshima University, Japan8Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan

9Graduate School of Frontier Science, The University of Tokyo, Ibaragi, Japan

1

1. Motivation2. Plasma Driven Permeation3. Schematic of Experimental System4. Summary of PDP results 5. Parametric scan6. Conclusion

Outline

2

Motivation

Future fusion reactors have two key issues

Recycling density control in steady state

operation

Particle retention

Safety Issues due to Tritium retention

Plasma Driven Permeation

Neutral atomic Hydrogen

H, CX measurement

Direct measurement of neutrals near plasma facing as well as non plasma

facing components 3

Plasma Driven Permeation

PLASMA

PFCsRecycling

Permeation

Neutral atomic flux

(H2)

(H2)

(H)

(eV and Sub eV range)

4

Non PFCs (e.g. behind divertor)

Top View of Quest

Multi channel spectrometer (200 - 900 nm)

VUV(Lyman)

Spectrometer(Fulcher spectrum for IH2 )PDP

System

NewPDP (#3)8.2 GHz -wave

(CD/heating)

Fast camera

Hard X-ray

Surface probe

-wave reflectometer

Probe/ Medium camera

Pump2.45 GHz

H array /medium camera

New PDP (#2)

IH2

IH2

8.2 GHz -wave

Movable probe

H, OII spectrum

5

Schematic of the measurement of the Plasma Driven Permeation

TMP

QMA

BaffleNi membrane

QUEST

Magnetic Shield

Lamp

Thermocouple

1.7 m

GV

60x1015

40

20

0

PDP(

H/m

2/s)

100806040200

Time (s)

Shot: 3188 - 3197 H2_3188 (87.4 kW) H2_3190 (79.2 kW) H2_3191 (69.1 kW) H2_3192 (58.4 kW) H2_3193 (48.1 kW) H2_3194 (37.4 kW) H2_3195 (27.9 kW) H2_3196 (19.0 kW) H2_3197 (11.4 kW) H2_3189 (4.65 kW)

2.0

1.5

1.0

0.5

0.0

I H (a

.u.)

0.600.500.40Time (s) 6

7

Wall conditioning during the experimental campaign (2009/06/02 to 2009/07/24)

5

4

3

2

1

0

(IO

IIdt

)/t (a

.u.)

3600320028002400Shot No.

QPDP and H fluence for > 1200 discharge shots

For more than 1200 discharges, QPDP follows H fluence and shows a linear relationship with H fluence (Q )

QPDP shows the fundamental linearly with the incident atomic fluence

0.012

4

0.12

4

12

4

10

Q(a

.u.)

3600320028002400Shot No.

10172

4

10182

4

10192

4

QPD

P (H

/m2 )

3600320028002400Shot No.

10172

4

10182

4

10192

4

QPD

P (H

/m2 )

0.012 4 6

0.12 4 6

12 4 6

10Q(a.u.)

Scattering from the linearity is to be studied in view of local plasma wall interaction as well as to understand its capabilities for

measuring atomic flux near PFCs　 as well as far PFCs8

Reproducibility in QPDP during discharge shots　 with similar operating parameters

•The QPDP is measured during plasma discharges having the similar operating condition•The QPDP shows a variation of ±3% •The part of this variation in QPDP may be due to the variation in the plasma discharges itself.•The Q however shows comparatively large variation.

4.0x10-9

3.5

3.0

2.5

2.0

QPD

P (a

.u.)

1680167516701665Shot No.

3.25308e-09±9.70699e-11 (±2.9 %)

±3% ±8%

0.30

0.20

0.10

0.00

Q(a

.u.)

1680167516701665Shot no.

0.1844 ±0.0147 ( ±7.9 %)

9

2.0x1018

1.5

1.0

0.5

QPD

P (H

/m2 )

2760275027402730Shot No.

1.085e18 ± 1.45e17 (13.3 %)

Sensitivity of PDP against local PWI(Change in magnetic configuration)

•The QPDP shows a variation of ±13% > standard•However variation in Q is ~ ± 9%•Large variation seems to be related to the change in neutrals by local PWI

0.40

0.35

0.30

0.25

0.20

Q(a

.u.)

2760275027402730Shot No.

0.287 ± 0.0268 ( 9.33 %)

10

30x1015

20

10

0 H2(H

/m2/

s)

100806040200Time (s)

Shot. 3423 - 3429 H2_3422 (15 ms) H2_3423 (20 ms) H2_3424 (30 ms) H2_3425 (50 ms) H2_3426 (90 ms) H2_3427 (150 ms) H2_3428 (200 ms) H2_3429 (300 ms) H2_3430 (15 ms)

Variation in PDP measurements during gas puff scan1.6x1018

1.2

0.8

0.4

0.0

QPD

P (H

/m2

)

300250200150100500Gas pulse (ms)

09/06/16 09/06/30 09/07/08 09/07/14 09/07/24

QPDP shows linear relationship with the Gas puff width. However the linearity with spectral fluences are relatively poor as compared to that with the gas puff times.

1.6x1018

1.2

0.8

0.4

0.0

QPD

P (H

/m2

)

0.50.40.30.20.10.0Q (a.u.)

09/06/16 09/06/30 09/07/08 09/07/14 09/07/24

1.6x1018

1.2

0.8

0.4

0.0

QPD

P (H

/m2

)

400x1033002001000Qmolecular (a.u.)

09/06/16 09/06/30 09/07/08 09/07/14 09/07/24

11

Effect of gas on plasma parameters i.e. Density and electron temperature

1.6x1018

1.2

0.8

0.4

0.0

QPD

P (H

/m2

)

300250200150100500Gas pulse (ms)

09/06/16 09/06/30 09/07/08 09/07/14 09/07/24

QPDP increases linearly with the Gas puff width (chamber pressure).

However edge plasma density does not show such relationship with gas puff width.

It indicate that the permeation is mainly related with the dissociated atomic density (flux) but not due to the plasma density itself.

300x1015

200

100

0

n wal

l (m

-3 )

3002001000Gas pulse (ms)

8

6

4

2

Te (eV

) Plasma density Te

12

60x1015

40

20

0

PDP(

H/m

2/s)

100806040200

Time (s)

Shot: 3188 - 3197 H2_3188 (87.4 kW) H2_3190 (79.2 kW) H2_3191 (69.1 kW) H2_3192 (58.4 kW) H2_3193 (48.1 kW) H2_3194 (37.4 kW) H2_3195 (27.9 kW) H2_3196 (19.0 kW) H2_3197 (11.4 kW) H2_3189 (4.65 kW)

Variation in permeated flux, PDP during a power scan

1.6x1018

1.2

0.8

0.4

0.0

QPD

P(H

/m2 )

100806040200RF Power (kW)

gas puff - 20 ms gas puff - 50 ms gas puff - 50 ms gas puff - 100 ms

At 50 kW RF power, QPDP shows a threshold value after which it rises more rapidly. Similar threshold can also be observed in H　 and molecular spectral fluences

0.5

0.4

0.3

0.2

0.1

0.0

Q(a

.u.)

100806040200RF Power (kW)

gas puff - 20 ms gas puff - 50 ms gas puff - 50 ms gas puff - 100 ms

400x103

300

200

100

0

Qm

olec

ular

(a.u

.)

100806040200RF Power (kW)

gas puff - 20 ms gas puff - 50 ms gas puff - 100 ms

13

Effect of RF power scan on plasma density and electron temperature

At 50 kW RF power, QPDP shows some threshold after which it rises more rapidly.

The similar threshold can be observed in the edge plasma density.

1.6x1018

1.2

0.8

0.4

0.0

QPD

P(H

/m2 )

100806040200RF Power (kW)

gas puff - 20 ms gas puff - 50 ms gas puff - 50 ms gas puff - 100 ms

200x1015

150

100

50

0

n w

all (

m-3

)

100806040200RF Power (kW)

5

4

3

2

1

Te (eV

)

Plasma density Te

14

QPDP as a function of H , Lyman- , molecular fluence and Density

QPDP shows a offset linear relationships with different spectral fluences and also edge plasma density

1.6x1018

1.2

0.8

0.4

0.0

QPD

P(H

/m2 )

150x101510050

Density (m-3 )

1.6x1018

1.2

0.8

0.4

0.0

QPD

P(H

/m2 )

0.50.40.30.20.10.0Q(a.u.)

gas puff - 20 ms gas puff - 50 ms gas puff - 50 ms gas puff - 100 ms

1.6x1018

1.2

0.8

0.4

QPD

P(H

/m2 )

400x1033002001000Qmolecular (a.u.)

gas puff - 20 ms gas puff - 50 ms gas puff - 100 ms

1.6x1018

1.2

0.8

0.4

0.0

QPD

P (H

/m2)

2.5x1062.01.51.00.50.0QLyman-(a.u.)

15

Permeated fluence increases linearly with the plasma discharge widths (> 5s)

PDP measurement during a discharge width scan

600x1015

400

200

0

PDP(

H/m

2/s)

100806040200Time (s)

29 s (discharge width) 20 s

10 s5 s

1s

(Shot No. 3598 - 3602)16x1018

12

8

4

0

QPD

P (H

/m2 )

3.02.01.00.0Hdt (a.u.)

Discharge Width (1 s - 29 s) (shot no. 3598 - 3602)

16x1018

12

8

4

0

QPD

P(H

/m2 )

302520151050 dis (s)

QPDP

16

600x1015

400

200

0

PDP(

H/m

2 /s)

100806040200Time (s)

30 ms @ 0.3s 80 ms @ 0.3s 80 ms @ 0.3s, 30 ms @ 10s, 20s 80 ms @ 0.3s, 30 ms @ 5,10,15,20,25 80 ms @ 0.3s, 30 ms @ 5,10,15,20,25

1.0

0.8

0.6

0.4

0.2

0.0 PDP

(Nor

mal

ised

)50403020100

Time (s)

H2_3576 H2_3577 H2_3578 H2_3579 H2_3580

600x1015

400

200

0

PDP(

H/m

2/s)

100806040200Time (s)

29 s (discharge width)

20 s10 s

5 s

1s

(Shot No. 3598 - 3602)1.0

0.8

0.6

0.4

0.2

0.0

PDP

(Nor

mal

ised

)

50403020100Time (s)

H2_3598 (29 s) H2_3599 (20 s) H2_3600 (10 s) H2_3601 (5 s)

Normalized PDP Flux for discharge pulse scan and gas puff scan

Rising or decay time constants of PDP does not depend on the incident atomic fluence

17

0.30

0.20

0.10

0.00

I H (a

.u.)

30252015105Time (s)

8000

6000

4000

2000

0

IH2 (a.u.)

30252015105 Ha__3703 H2_Q00_total_3703

0.30

0.20

0.10

0.00

I H (a

.u.)

30252015105Time (s)

8000

6000

4000

2000

0

IH2 (a.u.)

30252015105 Ha__3709 H2_Q00_total_3709

H

0.95

2.12

2.19

Effect of the hydrogen releasing from the chamber walls

600x1015

400

200

0

PDP(H

/m2 /s

)

100806040200Time (s)

H2_3703 H2_3709 H2_3716

0.30

0.20

0.10

0.00

I H (a

.u.)

30252015105Time (s)

8000

6000

4000

2000

0

IH2 (a.u.)

30252015105 Ha__3716 H2_Q00_total_3716

A large difference in PDP during three discharges is due to the change in released flux from the wall

All the operating parameter have been fixed during these three shots.

18

•Permeated flux is found linearly proportional to the incident H fluence (Q)during various type of plasma discharges

•The Permeated fluence is linearly proportional to the discharge width

•During RF power scan, a threshold is observed at 50 kW in QPDP as well as various spectroscopic fluence

•During gas puff scan the QPDP shows a linear relationship with the Gas puff width or chamber pressure. However the linearity with spectroscopic fluences are relatively poor as compared to that with the gas puff width.

Summary & Conclusion

•A long term working of the permeation probe without any cleaning procedure is observed

19

•The released gas from the walls (recycled flux) may highly affects the permeated flux PDP

•The rising or decay time constants of PDP does not depend on the incident fluence

•The PDP measurements seems to be a best estimates to know the neutral atomic flux near PFCs or far from PFCs as compared to the other spectral measurements

20

Thanks for your kind attention

21