A Vacuum Cold Bore Test Section at the CERN ISR
A 2 m helium cooled vacuum test section has been inserted into the CERN ISR to investigate problems which could be encountered in future cold bore proton machines. The UHV bore is cooled from the helium bath via a variable pressure gas filled space which enables operation at any temperature between 2.5 K and ambient. Temperature and degree of surface contamination can be remotely controlled. First observations from nominally clean and from hydrogen contaminated surfaces operating at temperatures close to 4.2 K are presented.
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.
Correlation between Fluoride Release, Microhardness and Solubility of High viscosity Glass Ionomers
This study was to measure and compare the amount of fluoride, microhardness and solubility of high viscosity glass ionomer and resin-reinforced glass ionomer during 84 days. Fuji IX GP EXTRA, Fuji IX GP, Fuji II LC and FiltekTM Z350XT stored in deionized water for 84 days to measure fluoride release, microhardness and solubility. As a result of measurement of fluoride release, all the glass ionomers showed the highest amount of fluoride release on day 1 and gradually decreased. Fuji IX GP EXTRA showed the highest amount of fluoride release and cumulative release. And Fuji IX GP and Fuji II LC showed no significant difference. Microhardness measurements showed that all experimental groups decreased 1 day after exposure to water. After 84 days, microhardness showed no significant difference between Fuji IX GP EXTRA and Fuji IX GP, and Fuji II LC was the lowest. In the solubility measurement, Fuji IX GP EXTRA, Fuji IX GP, and Fuji II LC increased rapidly to 21 days. After 21 days, there was no significant difference in the three groups. As a result, short term fluoride release affects solubility and microhardness, but long term fluoride release has no correlation. Through this study, the amount of fluoride, microhardness, and solubility of various glass ionomers were evaluated, and these properties could be applied clinically.