A. Komori

A. Sagara

H. Suzuki

K. Tsuchiya

M. Shoji

N. Noda

N. Ohyabu

O. Motojima

National Institute for Fusion Science (NIFS-Repository)

§ 15. Characteristics of Particle Balance in the Carbon Sheet Pump Nakashima, Y., Ishimoto, Y., Kobayashi, S., Yoshikawa, M., Yatsu, K. (Plasma Research Center, Unv. ofTsukuba), Tsuchiya, K. (Naka Fusion Research Establishment, JAERI) Sagara, A., Shoji, M., Suzuki, H., Noda, N., Komori, A., Ohyabu, N., Motojima, O. Reduction of hydrogen recycling is one of the important subjects for improvement of the plasma performance. First wall of fusion revice is exposed to charge- exchange fast neutrals and a large amount of hydrogen is resorbed from the wall. Carbon Sheet Pump (CSP) [1,2], which was revel oped for the reduction of hydrogen recycling in the Large Helical Device (LHD) was newly designed and investigated for the test on the actual plasma device. The subject of this collaboration is to understand the influence of charge-exchange fast neutral on hydrogen recycling quantitatively. Recently the pumping effect of CSP on the actual plasma revice was confirmed by using hot-ion plasmas produced in the GAMMA 10 tanrem mirror [3]. However, experimental results suggest that the carbon sheet adsorbs molecular hydrogens to a certain extent unrer the actual plasma circumstance. In order to investigate the above influence we installed a gate valve between the test module and GAMMA 1 0 which opens during plasma discharge. Fig.l shows the schematic view of the CSP module. CSP is shaping in <1> 170mm disk made oftwo-dimensional C/C sheet of 1.5mm thickness. CSP is installed with radiation shield for the baking in the test module. Charge-exchange fast neutrals emitted from the GAMMAI0 plasma are introduced via extension tube of 400mm in length. In front of the CSP, a rotational shutter which intercepts the incirent charge-exchange fast neutrals is mounted and the pumping effect is examined by using the shutter (CSP-on and CSP-off) shot by shot. Impurity gases during plasma discharge is also measured by quadrupole mass spectrometer (QMS) installed in the test module. Fig.2 shows the thermal resorption spectra of hydrogen (m/e=2) pressure before and after the installation of the gate val ve. The amount of desorbed hydrogen is reduced to about 20% by improvement the vacuum condition. Since particle flux is almost constant through the each experiment, pressure difference is thought to be dominated by the adsorbed molecular hydrogen. Fig.3 shows the correlation between the number of incident charge exchange neutral particles and that of the desorbed molecular hydrogen. Desorbed particles increase with incident charge-exchange fast neutrals. The ratio of desorbed particles to incident particles is estimated to be within the range of 1-0.3. Fig.l Schematic view of the test module of CSP and the experimental setup. a x 6 ~ iE 4 CI) ~ 0.... til 2 t ro 0.... Heating (-30A) -before 1 - -before 2 ---after 1 --after 2 o--~~~~~~~~~~ o 50 100 150 Time [sec 1 Fig.2 Thermal desorption spectra of hydrogen (m1e=2) pressure before and after improvement of the vacuum condition. O~~~~~~~~~~~ o 210'7 410'7 61017 810'7 Incident charge-exchange neutrals Fig.3 Correlation between the number of incident charge exchange neutral particles and that of des orbed molecular hydrogen. The solid line shows that incident particles are equal to desorbed particles. References 1) Sagara, A. et aI., J. Nucl. Mater. 220-222 (1995) 627. 2) Suzuki, H. et al., Trans. of Fusion TechnoI. 27 (1995) 523. 3) Nakashima, Y. etaI., J. NucI. Mater. 266-269 (1999)901. 83 

Characteristics of Particle Balance in the Carbon Sheet Pump

Characteristics of Particle Balance in the Carbon Sheet Pump

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