Synchrotron Radiation and Beam Tube Vacuum in a Very Large Hadron Collider, Stage 1 and Stage 2 Vlhc

Synchrotron radiation induced photodesorption in particle accelerators may lead to pressure rise and to beam-gas scattering losses, finally affecting the beam lifetime [1]. We discuss the beam tube vacuum in the low field Stage 1 and Stage 2 Very Large Hadron Collider VLHC. Since VLHC Stage 1 has a room temperature beam tube, a non-evaporable getter (NEG St101 strip) pumping system located inside a pumping antechamber, supplemented by lumped ion pumps for pumping methane is considered. In Stage 2, the ~100K beam screen, or liner, illuminated by the synchrotron radiation, is inserted into the magnet cold bore. Cryo-pumping is provided by the cold bore kept at 4.2K, through slots covering the beam screen surface. Possible beam conditioning scenarios are presented for reaching design intensity, both for Stage 1 and 2. The most important results are summarized in this paper.