Desing and construction of a horizontally placed superconducting magnet and its cryostat for an electron beam ion source

An electron beam ion source nicknamed NICE-I (Naked Ion Collision Experiments) has been constructed at IPP for studies of atomic processes in fusion plasmas. A super conducting magnet is adopted to generate a strong, stable and homogenious magnetic field to compress a high density electron beam. The solenoid is 1 m long, the inner diameter is 100 mm and the maximum magnetic field is 2T. It is placed horizontally and coaxially with a liquid nitrogen (L-N2) reservoir and a vaccum vessel. In order to fix their axes inmovable even when the reservoirs are cooled by L-N2 and He, a structure having spokes strained uniformly like a wheel is used between the vaccum vessel and the L-N2 reservoir and also between the L-N2 reservoir and the solenoid bore. The electrodes, such as the electron gun, the drift tubes and so on, are mounted on the radiation shields fixed on the L-N2 reservoir, and they are centered to the solenoid bore within the precision of 0.1 mm. The evapolation rate of L-He is about 1.4 l/h, which is not so much larger than the estimated value. This provides a continuous operation for 16 hours with a charge of 50 l L-He including the precooling of the reservoir. The ultimate pressure 4 x 10-10 Torr is achived in the vacuum vessel, and the residual gas pressure in the ionization region is expected to be much lower than 1 x 10-10 Torr. The consideration for mechanical strength and the heat conduction of the materials related to the design are described as well as the details of the structure. (author)