Abstract

Synchrotron radiation (SR) emission and interactions with the vacuum chamber walls have the potential to negatively impact the performance of future electron–positron colliders. The Beam Delivery System (BDS) of the Compact Linear Collider (CLIC) contains weak bending and multipole magnets that lead to less intense emissions than at circular colliders with similar centre-of-mass energies. However, the linear geometry more easily allows for multiple reflections of SR photons, that can travel further downstream in the accelerator and impact the detector region. In this study, the results of PLACET and Synrad+ simulations of photon emissions and reflections in the CLIC BDS at two energy stages of 380GeV and 3TeV are presented. Estimates are given for heating and outgassing caused by SR photons interacting with the vacuum chamber in the BDS. The occupancy levels in the tracking detectors coming from full-detector simulations in Geant4 are presented. Optimised beam pipe apertures are proposed for the forward detector region, as well as mitigation methods to ensure the safety and best possible performance of the detector.

Highlights

  • Synchrotron radiation (SR) is emitted by charged particles undergoing acceleration

  • The impact of SR was found to be a significant issue at Compact Linear Collider (CLIC), at both energy stages studied, especially when the reflections of the radiation are taken into account

  • The materials that can be used for the vacuum chamber walls have nonnegligible reflection probability up to a photon energy of about 30 keV

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Summary

Introduction

Synchrotron radiation (SR) is emitted by charged particles undergoing acceleration. This phenomenon is used in synchrotron light sources, such as ESRF [1], to study new materials, biological systems, and chemical reactions. The high energy of the electron and positron beams leads to the emission of a broad spectrum of synchrotron radiation, reaching MeV energies, in the bending and multipole magnets These emissions are less intense than at circular colliders with similar centre-of-mass energies. The linear geometry and low grazing angles increase the probability of SR photons reflecting from the beam pipe surface and travelling further downstream into the detector region. These particles could leave significant energy deposits in the CLIC detector (CLICdet) [11] and need to be studied carefully as a source of background that might degrade the detector performance. The beam pipe apertures in the detector region are revisited and methods to mitigate the occupancies determined are discussed

Photon interactions
Simulation treatment
Heating of the beam pipe
Photo-desorption and outgassing
C Beam pipe end in front of BeamCal
Impact in the detector region
Beam pipe aperture optimisation in the detector region
Photon distributions at the QD0 exit
Geometric acceptance of the photons
Hit densities and occupancies in tracking detectors
Mitigation methods
Findings
Summary and conclusions

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