Abstract

During the past decade, intense experimental studies on the heavy-ion induced molecular desorption were performed in several particle accelerator laboratories worldwide in order to understand and overcome large dynamic pressure rises caused by lost beam ions. Different target materials and various coatings were studied for desorption and mitigation techniques were applied to heavy-ion accelerators. For the upgrade of the CERN injector complex, a coating of the Super Proton Synchrotron (SPS) vacuum system with a thin film of amorphous carbon is under study to mitigate the electron cloud effect observed during SPS operation with the nominal proton beam for the Large Hadron Collider (LHC). Since the SPS is also part of the heavy-ion injector chain for LHC, dynamic vacuum studies of amorphous carbon films are important to determine their ion induced desorption yields. At the CERN Heavy Ion Accelerator (LINAC 3), carbon-coated accelerator-type stainless steel vacuum chambers were tested for desorption using $4.2\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Pb}}^{54+}$ ions. We describe the experimental setup and method, present the results for unbaked and baked films, and summarize surface characterizations such as secondary electron yield measurements, x-ray photoemission spectroscopy, and scanning electron microscopy studies. Finally, we present a high-energy scaling of lead-ion induced desorption yields from the $\mathrm{MeV}/\mathrm{u}$ to $\mathrm{GeV}/\mathrm{u}$ range.

Highlights

  • The electron cloud (EC) effect [1] is one important limitation for existing and future high-intensity particle accelerators with positively charged beams of short bunch spacing, as for the Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) at CERN

  • Desorption yield measurements of amorphous carbon. Both amorphous carbon coated vacuum chambers were investigated and effective ion-induced desorption yields have been measured for a fixed impact angle of  1⁄4 89:2 using 4:2 MeV=u Pb54þ ions

  • It is obvious that the measured amorphous carbon films show a much higher desorption yield than bare stainless steel

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Summary

Introduction

The electron cloud (EC) effect [1] is one important limitation for existing and future high-intensity particle accelerators with positively charged beams of short bunch spacing, as for the Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) at CERN. At CERN, clearing electrodes [2] and surface coatings [3] are presently explored in order to find and apply a suitable electron cloud mitigation technique to the SPS vacuum system. A promising mitigation technique is the coating of beam pipes with a thin film of amorphous carbon which exhibits a SEY close to 1.0. In the specific case of the SPS, several dipole vacuum chambers have been coated with amorphous carbon and are presently

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