Conditioning of SST-1 Tokamak Vacuum Vessel by Baking and Glow Discharge Cleaning

• Published in: Fusion engineering and design 2016-02, Vol.103, p.69-73
• Main Authors: Khan, Ziauddin, George, Siju, Semwal, Pratibha, Dhanani, Kalpeshkumar R., Pathan, Firozkhan S., Paravastu, Yuvakiran, Raval, Dilip C., Babu, Gattu Ramesh, Khan, Mohammed Shoaib, Pradhan, Subrata
• Format: Article
• Language: English
• Subjects: H-GDC; Nitrogen gas baking; plasma breakdown; SST-1 tokamak; UHV
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2015.12.020

•SST-1 Tokamak was successfully commissioned.•Vacuum vessel was pumped down to 4.5 × 10–8 mbar after baking and continuous GDC.•GDC reduced the water vapour by additional 57% while oxygen was reduced by 50%.•Under this condition, an initial plasma breakdown with current of 40 kA for 75 ms was achieved. Steady-state Superconducting Tokamak (SST-1) vacuum vessel (VV) adopts moderate baking at 110±10°C and the limiters baking at 250±10°C for ∼ 200h followed by glow discharge cleaning in hydrogen (GDC-H) with 0.15 A/m2 current density towards its conditioning prior to plasma discharge experiment. The baking in SST-1 reduces the water (H2O) vapor by 95% and oxygen (O2) by 60% whereas the GDC reduces the water vapor by an additional 57% and oxygen by another 50% as measured with residual gas analyzer. The minimum breakdown voltage for H-GDC in SST-1 tokamak was experimentally observed to 300V at 8 mbar cm. As a result of these adherences, SST-1 VV achieves an ultimate of 4.5×10−8 mbar with two turbo-molecular pumps with effective pumping speed of 3250 l/s. In the last campaign, SST-1 has achieved successful plasma breakdown, impurity burn through and a plasma current of ∼ 40 kA for 75ms.