A cross-section of the apparatus is shown in Fig. 1. The axis of rotation is horizontal. The liquid helium container, 1, is filled with 3 litres of liquid. A copper thermal shield, 2, surrounds the helium container, and is cooled with the evaporated helium gas through a sintered copper heat exchanger, 3. The vacuum insulation is provided by a third stainless steel cylinder, 4.
Each cylinder is soldered at one side onto a flange and sealed on the other side: with an indium seal, 5, for the helium dewar and with a viton seal, 6, for the vacuum jacket. The copper radiation shield is only screwed onto its flange. No problem was found with the indium seal during the different tests. The viton seal was not so satisfactory with the vibrations because a good vacuum (10 -6 mm Hg) is lost after some time of rotation. Nevertheless, once the liquid helium container filled, this imperfection does not hinder good performance of the cryostat.
Before running the cryostat was dynamically tested but no special care was taken to balance it, other than a correct construction of the flanges and cylinders. No vibration problems appeared at speeds up to 1 660 rpm. The cryostat being empty or filled with liquid helium. The helium transfer coupling is made with two special rotating seals, 7 and 8,