Cleaning Insertions and Collimation Challenges

Abstract

High-performance collimation systems are essential for operating efficiently modern hadron machine with large beam intensities. In particular, at the LHC the collimation system ensures a clean disposal of beam halos in the superconducting environment. The challenges of the HL-LHC study pose various demanding requests for beam collimation. In this paper we review the present collimation system and its performance during the LHC Run 1 in 2010-2013. Various collimation solutions under study to address the HL-LHC requirements are then reviewed, identifying the main upgrade baseline and pointing out advanced collimation concept for further enhancement of the performance. Present LHC CollimationIn this introductory section the present LHC collimation system is reviewed. Its main features are presented and the highlight performance achievements during the LHC Run 1 are recalled. The possible limitations and challenges for the collimation in the HL-LHC era are then discussed. Introduction to LHC multi-stage collimationThe LHC collimation system is designed to safely dispose of beam losses in order to reduce the risk of quenches of superconducting magnets and damage of accelerator components. The cleaning functionality is required in case of unavoidable transverse betatron -as well as off-momentum losses. For this purpose, two dedicated warm LHC insertions address betatron (IR7) and momentum (IR3) cleaning separately [1]. A very efficient halo cleaning, as required to operate with unprecedented stored beam energies in a superconducting collider, is achieved through a multi-stage cleaning. This is illustrated

Performance of the Large Hadron Collider cleaning system during the squeeze: Simulations and measurements

“…In section VI we evaluate the loads on the collimators in the HL-LHC, for the most pessimistic loss scenario allowed at full energy. This corresponds to a 0.2 h beam lifetime over 10 s [19,20], giving a total loss power of about 1 MW.…”

Hollow electron lenses for beam collimation at the High-Luminosity Large Hadron Collider (HL-LHC)

“…The smallest inner radius for halo control at the maximum LHC beam energy of 7 TeV was identified at 3.6 , where = √ is the RMS beam size, for which we assume a normalized emittance = 2.5 μm. This ensures a clearance of about 3 with respect to the nominal opening of 6.7 the primary collimators in Pt7 [15].…”

“…Even if the performance of the LHC collimation system so far was very good, as stored energies in excess of 300 MJ were routinely handled without quenches triggered by beam losses on the collimation system [12][13][14], uncertainties apply to the extrapolations to conditions at the HL-LHC, with doubled bunch current, smaller emittances, and higher beam energies. Various means to improve the LHC collimation performance are therefore under investigation [15]. Some important upgrades already took place in the LHC Long Shutdown 2, which covers the period 2019-2021, with a first phase of the planned low-impedance upgrade of the betatron collimators and with the improvement of the dispersionsuppressor cleaning [15].…”

“…Various means to improve the LHC collimation performance are therefore under investigation [15]. Some important upgrades already took place in the LHC Long Shutdown 2, which covers the period 2019-2021, with a first phase of the planned low-impedance upgrade of the betatron collimators and with the improvement of the dispersionsuppressor cleaning [15].…”

Heavy-Ion Operation of HL-LHC

“…Although recent quench test measurements [7,23] have indicated that the quench limit is somewhat higher than estimated in the past, quenches remain likely to occur with the upgraded Pb-Pb luminosity. For this reason, priority has been given to the installation of collimators in the dispersion suppressors on either side of the ALICE experiment as part of the High-Luminosity LHC upgrade [24].…”