Measurement of the Plasma Driven Permeation Flux in the Spherical Tokamak QUEST S. K. Sharma 1 H. Zushi 2, I. Takagi 3, Y.Hisano 1, M. Sakamoto 2, Y. Higashizono 2, T. Shikama 3, S. Morita 4, T. Tanabe 1, N. Yoshida 2, K. Hanada 2, M. Hasegawa 2, O. Mitarai 5, K. Nakamura 2, H. Idei 2, K. N. Sato 2, S. Kawasaki 2, H. Nakashima 2, A. Higashijima 2, Y. Nakashima 6, N. Nishino 7, Y.Hatano 8, A. Sagara 4, Y. Nakamura 4, N. Ashikawa 4, T. Maekawa 3, Y. Kishimoto 3, Y. Takase 9 and QUEST Group 1 IGSES, Kyushu University, Kasuga, Fukuoka, , Japan 2 RIAM, Kyushu University, Kasuga, Fukuoka, , Japan 3 Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University, Japan 4 National Institute for Fusion Science, Toki, Japan 5 Kyushu Tokai University, Toroku, Kumamoto , Japan 6 Plasma Research Center, University of Tsukuba, Japan 7 Department of Mechanical System Engineering, Graduate School of Engineering, Hiroshima University, Japan 8 Hydrogen Isotope Research Center, Toyama University, Toyama , Japan 9 Graduate School of Frontier Science, The University of Tokyo, Ibaragi, Japan 1

1.Motivation 2.Plasma Driven Permeation 3.Schematic of Experimental System 4.Summary of PDP results 5.Parametric scan 6.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 PLASMAPLASMA PFCs Recycling Permeation Neutral atomic flux (H 2 ) (H) (eV and Sub eV range) 4 Non PFCs (e.g. behind divertor)

Top View of Quest Multi channel spectrometer ( nm) VUV(Lyman) Spectrometer (Fulcher spectrum for I H2 ) PDP System New PDP (#3) 8.2 GHz  -wave (CD/heating) Fast camera Hard X-ray Surface probe  -wave reflectometer Probe/ Medium camera Pump 2.45 GHz H  array /medium camera New PDP (#2) I H2 8.2 GHz  -wave Movable probe H , OII spectrum 5

Schematic of the measurement of the Plasma Driven Permeation TMP QMA Baffle Ni membrane QUESTQUEST Magnetic Shield Lamp Thermocouple 1.7 m GV 6

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

Q PDP and H  fluence for > 1200 discharge shots For more than 1200 discharges, Q PDP follows H  fluence and shows a linear relationship with H  fluence (Q  ) Q PDP 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 PFCs as well as far PFCs 8

Reproducibility in Q PDP during discharge shots with similar operating parameters The Q PDP is measured during plasma discharges having the similar operating condition The Q PDP shows a variation of ± 3% The part of this variation in Q PDP may be due to the variation in the plasma discharges itself. The Q  however shows comparatively large variation. ± 3% ± 8% 9

Sensitivity of PDP against local PWI (Change in magnetic configuration) The Q PDP shows a variation of ±1 3% > standard However variation in Q  is ~ ± 9% Large variation seems to be related to the change in neutrals by local PWI 10

Variation in PDP measurements during gas puff scan Q PDP 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. 11

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

Variation in permeated flux,  PDP during a power scan At 50 kW RF power, Q PDP shows a threshold value after which it rises more rapidly. Similar threshold can also be observed in H  and molecular spectral fluences 13

Effect of RF power scan on plasma density and electron temperature At 50 kW RF power, Q PDP shows some threshold after which it rises more rapidly. The similar threshold can be observed in the edge plasma density. 14

Q PDP as a function of H , Lyman- , molecular fluence and Density Q PDP shows a offset linear relationships with different spectral fluences and also edge plasma density 15

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

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

HH Effect of the hydrogen releasing from the chamber walls 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 Q PDP as well as various spectroscopic fluence During gas puff scan the Q PDP 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

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