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

1. 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, Japan 2RIAM, 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, Japan 5Kyushu Tokai University, 9-1-1 Toroku, Kumamoto 862-8652, Japan 6Plasma Research Center, University of Tsukuba, Japan 7Department of Mechanical System Engineering, Graduate School of Engineering, Hiroshima University, Japan 8Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan 9Graduate School of Frontier Science, The University of Tokyo, Ibaragi, Japan

2. Outline Motivation Plasma Driven Permeation Schematic of Experimental System Summary of PDP results Parametric scan Conclusion

3. Motivation Future fusion reactors have two key issues density control in steady state operation Recycling 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

4. Plasma Driven Permeation PFCs Recycling (H2) P L A S M A (H) Permeation (H2) Neutral atomic flux Non PFCs (e.g. behind divertor) (eV and Sub eV range)

5. New PDP (#2) Top View of Quest New PDP (#3) Fast camera H, OII spectrum 8.2 GHz -wave (CD/heating) Surface probe IH2 -wave reflectometer Probe/ Medium camera IH2 Movable probe Hard X-ray 8.2 GHz -wave 2.45 GHz Pump VUV(Lyman) H array /medium camera Multi channel spectrometer (200 - 900 nm) PDP System Spectrometer (Fulcher spectrum for IH2 )

6. Schematic of the measurement of the Plasma Driven Permeation Ni membrane Magnetic Shield Baffle GV Q U E S T Lamp QMA Thermocouple TMP 1.7 m

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

8. 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 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 PFCsas well as far PFCs

9. Reproducibility in QPDP during discharge shotswith similar operating parameters ±3% ±8% • 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 QPDPmay be due to the variation in the plasma discharges itself. • The Qhowever shows comparatively large variation.

10. 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

11. Variation in PDP measurements during gas puff scan 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.

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

13. Variation in permeated flux, PDP during a power scan 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

14. 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.

15. 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

16. PDP measurement during a discharge width scan Permeated fluence increases linearly with the plasma discharge widths (> 5s)

17. Normalized PDP Flux for discharge pulse scan and gas puff scan Rising or decay time constants of PDPdoes not depend on the incident atomic fluence

18. Effect of the hydrogen releasing from the chamber walls 2.19 2.12 0.95 H All the operating parameter have been fixed during these three shots. A large difference in PDP during three discharges is due to the change in released flux from the wall

19. Summary & Conclusion • Permeated flux is found linearly proportional to the incident H fluence (Q)during various type of plasma discharges • A long term working of the permeation probe without any cleaning procedure is observed • 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. • During RF power scan, a threshold is observed at 50 kW in QPDP as well as various spectroscopic fluence • The Permeated fluence is linearly proportional to the discharge width

20. The released gas from the walls (recycled flux) may highly affects the permeated flux PDP • The rising or decay time constants of PDPdoes 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

21. Thanks for your kind attention