DocumentCode :
158958
Title :
Comparative study of glow discharge wall conditioning using H2 and Ar-H2 gas mixture of ADITYA Tokamak vacuum vessel
Author :
Jadeja, K.A. ; Patel, K.M. ; Tanna, R.L. ; Sangwan, Deepak ; Acharya, K.S. ; Patel, N.D. ; Raval, M.K. ; Kumar, Pranaw ; Bhatt, S.B. ; Ghosh, Joydeb
Author_Institution :
Inst. for Plasma Res., Bhat, India
fYear :
2014
fDate :
Sept. 28 2014-Oct. 3 2014
Firstpage :
673
Lastpage :
676
Abstract :
Low temperature glow discharge wall conditioning (GDC) using H2 gas is effective in reduction of oxygen and carbon (low-Z) contain impurities on near surface region of vessel wall. The high retention of hydrogen in vessel wall/components due to long operation of H2 GDC increases hydrogen out-gassing during tokamak operation and affects the production of high temperature plasma. The hydrogen retention can be reduced using inert gas GDC by sputter cleaning for short duration. But in that case the out-gassing rate of inert gas increases, that again impairs the plasma performance. To overcome above problems, the GDC with hydrogen-inert gas mixture can be used for better removal of C and O surface contaminants and low hydrogen retention in surface. In ADITYA tokamak, H2-GDC is carried out regularly after plasma operation, while the GDC with argon-hydrogen (Ar-H2) mixture has been experimentally tested to observe the reduction of oxygen and carbon impurities along with low hydrogen retention. In Ar-H2 GDC, the reason being the formation of ArH+ hydride ions, which has quite long life and more energy compared to H2+ ions formed in H2 GDC for breaking the bond of wall molecules. A systematic comparative study of H2 GDC and Ar-H2 Mixture GDC by changing the mixture ratio has been carried out in ADITYA tokamak. The relative levels of oxygen and carbon contain impurities have been measured using residual gas analyzer in both GDC´s. We have observed a substantial reduction in oxygen and carbon impurities with a significant improvement in wall condition with Ar-H2 GDC compared to the H2 GDC. The effect of wall conditioning by Ar-H2 GDC on the performance of high temperature plasma operation will be presented in this paper.
Keywords :
Tokamak devices; argon; carbon; gas mixtures; glow discharges; hydrogen; oxygen; plasma impurities; plasma toroidal confinement; ADITYA tokamak vacuum vessel; Ar-H2; Ar-H2 gas mixture GDC; C; C surface contaminant; H2-GDC; O surface contaminant; O2; carbon impurity; high-temperature plasma operation; hydrogen out-gassing; hydrogen retention; hydrogen-inert gas mixture; low-temperature glow discharge wall conditioning; oxygen impurity; plasma performance; sputter cleaning; tokamak operation; Argon; Carbon; Discharges (electric); Hydrogen; Impurities; Plasma temperature;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Discharges and Electrical Insulation in Vacuum (ISDEIV), 2014 International Symposium on
Conference_Location :
Mumbai
Print_ISBN :
978-1-4799-6750-6
Type :
conf
DOI :
10.1109/DEIV.2014.6961772
Filename :
6961772
Link To Document :
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