To reduce the operating noise in liquid hydrogen targets, the amount of material in the beam entrance and exit windows should be minimal. Lawsonite is a good material for target windows, since a sheet of Lawsonite is strong, keeps its elasticity at low temperatures, has a low density and small Z. A number of targets with Lawsonite windows have been developed at the Institute.
The inner vessel of the 50 cm target (Fig. l) is made of 144 mm diameter tubing with 1 mm wall thickness, to the end of which flanges for fixing the Lawsonite windows, 3, are soldered. The demountable vacuum jacket, 9, consists of three sections: ring 11 for fastening the inner vessel and two 168 mm diameter cylindrical containers. The design of the sealing of the Lawsonite windows to the ends of the vacuum jacket is the same as to the inner vessel. The inner vessel of the target is hung on the side tube 12 the upper part of which is soldered to the tube of the vacuum jacket. The cylindrical part of the inner vessel of the target is insulated by the multi-layer vacuum insulation, 8, which consists of 40 layers of 50 #m thick fibre glass and 40 The authors are with the Joint Institute for Nuclear Research Dubna, USSR. Prib i Tekh Eksper No 3 (1971) 52.