Cold Bore Experiments at CERN ISR

At the beginning of 1978 a new cryostat was installed in the ISR to study the vacuum behaviour of a cold chamber in presence of intense proton beams. The cryostat permits cooling 1.3 m of the elliptical standard ISR vacuum chamber to any temperature in the range from 2.3 K to ¿ 200 K. The connection of the `Cold Bore´ to room temperature regions is made via elliptical bellows without baffles for thermal radiation. Proton beams of intensities up to 40 A were circulating inside the Cold Bore in different experimental conditions for times of the order of 24 h. In one experiment about 10 monolayers of H2 were condensed at 2.3 K to produce the situation which, according to theoretical estimates, should provide the highest chance of observing a beam induced pressure rise. In another experiment, the Cold Bore was exposed to air and subsequently pumped and cooled without baking, to simulate the case of a cold unbaked machine. Under all conditions the vacuum remained perfectly stable. Although experiments are still in progress, the available results indicate that the vacuum of a cold bore machine would be stable to above 40 A in the ISR geometry.