Beam heat load and pressure rise in a cold vacuum chamber

Abstract

The beam heat load and the pressure in the vacuum chamber of the cold bore superconducting undulator installed at ANKA (ANgstrom source KArlsruhe) have been monitored for almost two years. Possible sources of the observed heat load could be synchrotron radiation from upstream magnets, image currents, electron and ion bombardment. In this paper, the various possible contributions to the heat load are discussed and compared with experimental results. The dynamic pressure increases nonlinearly with the average beam current. The current where it assumes a maximum varies both with the bunch intensity and with the initial vacuum pressure. A correlation between the heat load and the dynamic pressure has been observed. This study suggests that electron bombardment could explain the beam heat load and pressure rise observed for a bunch length of 10 mm.

COLDDIAG: A Cold Vacuum Chamber for Diagnostics

“…Studies performed with the cold bore superconducting undulator installed at the synchrotron radiation source ANKA suggest that the main contribution to the beam heat load is due to secondary electron bombardment. The electron bombardment model appears to be consistent with the beam heat load and the dynamic pressure rise observed for bunch lengths of about 10 mm [2]. Low energy electrons (few eV) are accelerated by the electric field of the beam towards the wall of the vacuum chamber, introducing heat to the cold liner and causing nonthermal desorption of gas from the cryogenic surface.…”

Can electron multipacting explain the pressure rise in a cold bore superconducting undulator?

“…Studies performed on the cold bore superconducting undulator installed at ANKA indicate that a simple model of electron bombardment could explain the beam heat load and observed pressure rise during normal user operation [6]. In this paper we go a step further solving the equations of gas dynamic balance in a cold vacuum chamber exposed to synchrotron radiation and electron bombardment.…”

Measurements of x-ray scattering from accelerator vacuum chamber surfaces, and comparison with an analytical model

“…The distribution of photon absorption sites, as well as the photon energy spectrum, is an important input into the computation of quantities such as the distribution and energy of primary photoelectrons which seed the electron cloud, and the distribution of heat load on the chamber wall [2][3][4][5][6][7]. This subject is also important for other areas of accelerator physics and engineering, such as long-range coherent synchrotron radiation wakefield in accelerator vacuum chambers [8] and performance of superconducting rf cavities [9].…”