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.
Beam Induced Gas Desorption in the CERN Intersecting Storage Rings
The maximum beam intensity achieved in the ISR has been limited up to now by the beam induced pressure rise which builds up with the stacked proton current. This pressure increase can be explained by ion induced gas desorption from the vacuum chamber. The pressure P, as a function of the stacked proton current I, can be described in good approximation by P = Po/[1-(k?/S)I], where Po is the pressure without beam, S the pumping speed, ? the net gas desorption coefficient in molecules per incident gas ion and ? is a constant. This concept shows the existence of a critical current at which the pressure goes to infinity. The desorption coefficient depends on the primary ion energy, the type of ions and above all, on the surface conditions. Surface treatments yielding low and even negative values of ? are discussed together with experimental results obtained.
Neurorehabilitation: A Disciplined Disciplining Discipline
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