Abstract
Preliminary studies performed with the cold bore superconducting undulator installed in the ANKA (Angstrom source Karlsruhe) storage ring suggest that the beam heat load is mainly due to the electron wall bombardment. Electron bombardment can both heat the cold vacuum chamber and induce an increase in the pressure because of gas desorption. In this contribution we compare the measurements of the pressure in a cold bore performed in the electron storage ring ANKA with the predictions obtained using the equations of gas dynamic balance in a cold vacuum chamber exposed to synchrotron radiation and electron bombardment. The balance results from two competing effects: the photon and electron stimulated desorption of the gas contained in the surface layer of the chamber wall and of the gas cryosorbed, and the cryopumping by the cold surface. We show that photodesorption alone cannot explain the experimental results and that electron multipacting is needed to reproduce the observed pressure rise. Electron bombardment can at the same time explain the observed beam heat load.
Highlights
In order to produce synchrotron radiation of highest brilliance, third generation synchrotron sources make use of insertion devices (IDs)
One of the key issues for the development of superconducting insertion devices (SCIDs) is the understanding of the beam heat load to the cold vacuum chamber
We show that the observed pressure rise can be explained by the occurrence of electron multipacting and not by photodesorption alone
Summary
In order to produce synchrotron radiation of highest brilliance, third generation synchrotron sources make use of insertion devices (IDs). The state of the art available today for IDs is the permanent magnet technology with magnet blocks placed inside the vacuum of the storage ring. Superconducting undulators can reach, for the same gap and period length, higher fields even with respect to CPMU devices, allowing to increase the spectral range and the brilliance. At ANKA (Angstrom source Karlsruhe) we are running a research and development program on superconducting insertion devices (SCIDs). One of the key issues for the development of SCIDs is the understanding of the beam heat load to the cold vacuum chamber. The beam heat load is a fundamental input parameter for the design of SCIDs since it is needed to specify the cooling power
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