A double-loop helium refrigeration system is developed to stabilize the operating conditions of a liquid-hydrogen rapid-cycling bubble chamber. The system makes it possible to reduce the amount of liquid hydrogen used to a minimum and thus to localize the dangerously explosive zone within the boundaries of the vacuum housing. Under operating conditions, the system maintains temperature and pressure to an accuracy of +/-0.005 K and +/-0.01 atm, respectively, Consumption of liquid helium is within 60 1/day.

A precision liquid hydrogen bubble chamber with rapid cycling capability and a photographed volume of 150 × 70 × 50 mm3 has been constructed to study short-living elementary particles. Its refrigeration system is operated with liquid helium. The chamber body, manufactured from the polycarbonate Lexan®, is almost free of vibrations due to the innovative expansion system with two pistons operating in opposite directions. The chamber operates with 5 ms cycle time and a rate up to 30 s−1. The chamber has already been cycled 6.7 million times and about 0.3 million pictures have been taken. At the hydrogen temperature of 29.8 K a track density of 150 bubbles/cm has been achieved with bubble diameters of 25 μm.

A liquid hydrogen bubble chamber now under construction is described. It is intended for operation at the synchrophasotron in a nominal magnetic field of 15 kG. The chamber body is a steel casting with a neck welded to it to take the piston-type expansion mechanism. Synchronization of the chamber with the accelerator is achieved by means of a transistorized electronic control panel. (A.G.W.)