Abstract
The beam heat load is an important input parameter needed for the cryogenic design of superconducting insertion devices. Theoretical models taking into account the different heating mechanisms of an electron beam to a cold bore predict smaller values than the ones measured with several superconducting insertion devices installed in different electron storage rings. In order to measure and possibly understand the beam heat load to a cold bore, a cold vacuum chamber for diagnostics (COLDDIAG) has been built. COLDDIAG is equipped with temperature sensors, pressure gauges, mass spectrometers as well as retarding field analyzers which allow to measure the beam heat load, total pressure, and gas content as well as the flux of particles hitting the chamber walls. COLDDIAG was installed in a straight section of the Diamond Light Source (DLS). In a previous paper the experimental equipment as well as the installation of COLDDIAG in the DLS are described [S. Gerstl et al., Phys. Rev. ST Accel. Beams 17, 103201 (2014)]. In this paper we present an overview of all the measurements performed with COLDDIAG at the DLS and their detailed analysis, as well as impedance bench measurements of the cold beam vacuum chamber performed at the Karlsruhe Institute of Technology after removal from the DLS. Relevant conclusions for the cryogenic design of superconducting insertion devices are drawn from the obtained results.
Highlights
Superconducting insertion devices (SCIDs) are employed in different synchrotron light sources in order to increase the offered photon flux and brilliance with respect to permanent magnet based insertion devices
The cold section of COLDDIAG is studied in three steps, allowing to differentiate between the impedance generated by the liner itself (490 mm), the thermal transitions from the cold liner to the 50 K shield (554 mm) and the finger bellows from the 50 K shield to the warm sections (850 mm, see Fig. 14)
No correlation between the beam heat load and the pressure has been observed. This is different from the observations performed at ANKA with the superconducting undulator developed with ACCEL GmbH [2], where a correlation between beam heat load and pressure rise, which can be explained only by electron multipacting [23], was observed
Summary
The beam heat load is an important input parameter needed for the cryogenic design of superconducting insertion devices. Theoretical models taking into account the different heating mechanisms of an electron beam to a cold bore predict smaller values than the ones measured with several superconducting insertion devices installed in different electron storage rings. In order to measure and possibly understand the beam heat load to a cold bore, a cold vacuum chamber for diagnostics (COLDDIAG) has been built. COLDDIAG is equipped with temperature sensors, pressure gauges, mass spectrometers as well as retarding field analyzers which allow to measure the beam heat load, total pressure, and gas content as well as the flux of particles hitting the chamber walls. In a previous paper the experimental equipment as well as the installation of COLDDIAG in the DLS are described [S. Relevant conclusions for the cryogenic design of superconducting insertion devices are drawn from the obtained results
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