Characteristics of the DC separator in the TRISTAN main ring

A TRISTAN main ring equipped with a total of 16 DC separators are designed and constructed. The main ring requires a maximum electrostatic field of about 30 kV/cm, and the pressure should be maintained on the order of 109 Torr or less. This report describes the structures of the DC separators and test results on them. Two types of high-voltage feedthroughs, the Al type and HP type, are used to improve the efficiency of heat dissipation. A test of the air-tightness of the feedthroughs are performed. They are also subjected to a high voltage resistance test after performing direct current discharge cleaning with nitrogen gas at 1018 ions/cm2. Effect of discharge cleaning on breakdown frequency is examined to determine the optimum ion dose for the conditioning of the feedthroughs. The frequency obviously decreases at ion dose of above 1 x 1018 ions/cm2. Discharge cleaning with hydrogen gas has been considered to be effective for removing organic contaminants from separators. Thus measurement is made to see the behaviours of major gas components during H2 glow discharge cleaning. It is suggested that chemical reactions involving hydrogen atoms, in addition to hydrogen ions, are serving for the cleaning, whereas only the sputtering of ions plays the cleaning role in the case of helium. Other measurements including the pressure rise and leakage current for a set of four separators are also made. Performance of the DC separators is discussed based on the test results obtained. (Nogami, K.)