Preliminary insulation design for transmission line of CFETR NNBI test platform

In order to meet the requirements of China Fusion Engineering Test Reactor (CFETR) for neutral beam injector system, a Negative-ion Based Neutral Beam Injector system(NNBI) test platform will be established by Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). The high voltage Transmission Line (TL) plays an important role in the NNBI system, connecting the ion source and the power supply system. The TL will be insulated by gas insulation technology, that is, Gas Insulated Transmission Line (GITL). This paper mainly focuses on the insulation dimension design of TL2, which is the longest and main section of the TL. Firstly, the method of determining the design criteria of TL2 gas insulation is given, the gap required by gas insulation is analyzed and the condition of electric field strength to prevent the movement of conductive particles is put forward; secondly, the basic design principles of TL2 insulation design are put forward and the design method of wall thickness of TL2 central conductor and grounding shell is given. Finally, according to the above insulation requirements and design methods, some basic structural parameters of TL2 of the NNBI test platform are determined, including the outer radius and wall thickness of the central conductor and the inner radius and wall thickness of the grounding shell, which lays a foundation for the subsequent detailed design of TL.