Design of vacuum system for NCST spherical tokamak

The NanChang Spherical Tokamak (NCST) is a new compact tokamak with an aspect ratio of R/a = 1.67. The vacuum system is one of the most important sub-systems of the tokamak device and has been designed especially for the NCST device. It consists of three main parts: a pumping system, a gas puffing system, and a wall conditioning system. The pumping system includes two turbo-molecular pumps, a cryopump, and two rotary pumps. The gas puffing system consists of a gas supply, transfer lines, a gas reservoir, pressure gauges, and piezoelectric valves. The wall conditioning system includes baking and glow discharge cleaning functions. The vacuum system and related experimental results are described in detail in this paper. The test results indicate that the NCST vacuum system is reliable. Inside the vessel, the ultimate pressure reached 4.2 × 10−6 Pa after 307 h of pumping. The upgraded gas puffing system can accurately control the gas entering the vacuum vessel. The wall conditioning systems, such as those for baking and glow discharge cleaning, also play a very important role in plasma operation. The plasma discharge results show that the basic function of the vacuum system meets the essential requirements of the present experiments on the NCST tokamak.