Beam-loss induced pressure rise of Large Hadron Collider collimator materials irradiated with158  GeV/uIn49+ions at the CERN Super Proton Synchrotron

E Mahner,H Vincke,I Efthymiopoulos,E Page,J Hansen

doi:10.1103/physrevstab.7.103202

Beam-loss induced pressure rise of Large Hadron Collider collimator materials irradiated with158 GeV/uIn49+ions at the CERN Super Proton Synchrotron

E Mahner, H Vincke + Show 3 more

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https://doi.org/10.1103/physrevstab.7.103202

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Abstract

During heavy ion operation, large pressure rises, up to a few orders of magnitude, were observed at CERN, GSI, and BNL. The dynamic pressure rises were triggered by lost beam ions that impacted onto the vacuum chamber walls and desorbed about 10 4 to 10 7 molecules per ion. The deterioration of the dynamic vacuum conditions can enhance charge-exchange beam losses and can lead to beam instabilities or even to beam abortion triggered by vacuum interlocks. Consequently, a dedicated measurement of heavy-ion induced molecular desorption in the GeV/u energy range is important for LHC ion operation. In 2003, a desorption experiment was installed at the SPS to measure the beam-loss induced pressure rise of potential LHC collimator materials. Samples of bare graphite, sputter coated (Cu, TiZrV) graphite, and 316 LN stainless steel, were irradiated under grazing angle with 158 GeV/u indium ions. After a description of the new experimental set-up, the results of the pressure rise measurements are presented, and the derived desorption yields are compared with data from other experiments.

Highlights

An intense experimental program was started at the CERN Heavy Ion Accelerator (LINAC 3) in November 2000 to measure the beam-loss induced molecular desorption of Pb53 ions at 4:2 MeV=u in order to prepare the Low Energy Ion Ring (LEIR) vacuum system for operation with heavy ions under Large Hadron Collider (LHC)-type conditions
The experiment consists of a rotatable 316 LN stainless steel vacuum chamber with an inner diameter of 400 mm and a height of 292 mm. This central chamber is pumped with a turbo molecular pumping (TMP) group, a 400 ‘=s sputter ion pump (SIP), and a 1200 ‘=s titanium sublimation pump (TSP)
Pressure measurements are made with a BayardAlpert gauge (BAG) and a quadrupole residual gas analyzer (RGA), both calibrated

Summary

Introduction

An intense experimental program was started at the CERN Heavy Ion Accelerator (LINAC 3) in November 2000 to measure the beam-loss induced molecular desorption of Pb53 ions at 4:2 MeV=u in order to prepare the Low Energy Ion Ring (LEIR) vacuum system for operation with heavy ions under Large Hadron Collider (LHC)-type conditions. Effective desorption yields of up to 2 104 molecules=ion were measured for standard stainless steel vacuum chambers [1]. At RHIC, a yield of 1:5 107 molecules=ion was reported for Au79 ions with an energy of about 10 GeV=u [6]. This value is about 3 orders of magnitude higher than the yields measured previously at LINAC 3. This latter observation, indicating a strong effect of the ion energy on the desorption rate, motivated the Super Proton Synchrotron (SPS) experiment described in this paper. The measurements were done with In49 ions at 158 GeV=u, an energy very close to the 177 GeV=u injection energy of Pb82 into the LHC

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