Abstract
The heat load generated by an electron cloud in the cold arcs of the Large Hadron Collider (LHC) is a concern for operation near and beyond nominal beam current. We report the results of simulation studies, with updated secondary-emission models, which examine the severity of the electron heat load over a range of possible operation parameters, both for the nominal LHC and for various luminosity-upgrade scenarios, such as the so-called ``full crab crossing'' and ``early separation'' schemes, the ``large Piwinski angle'' scheme, and a variant of the latter providing ``compatibility'' with the (upgraded) LHCb experiment. The variable parameters considered are the maximum secondary-emission yield, the number of particles per bunch, and the spacing between bunches. In addition, the dependence of the heat load on the longitudinal bunch profile is investigated.
Highlights
The performance of the Large Hadron Collider (LHC) and of its possible future upgrades may be limited by the electron cloud which is built up both through photoemission from synchrotron radiation and by a beaminduced multipacting process [1,2,3,4]
At 7 TeV beam energy, the critical energy of synchrotron radiation is about 44 eV, which is close to the energy where the photoemission yield is maximum for many materials
A primary concern for the LHC is the additional heat load due to the electron cloud that is deposited on the beam screen, a perforated tube inserted into the cold bore of the superconducting magnets in order to protect the cold bore from synchrotron radiation and ion bombardment [7]
Summary
The performance of the Large Hadron Collider (LHC) and of its possible future upgrades may be limited by the electron cloud which is built up both through photoemission from synchrotron radiation and by a beaminduced multipacting process [1,2,3,4]. Some of the synchrotron radiation photons, hitting the metallic beam screen inside the beam pipe, produce photoelectrons These photoelectrons are accelerated in the field of the bunch that has emitted the photons, passing by quasisimultaneously, to up to 200 eV and they reach the opposite beam pipe wall after a few ns, before the following bunch arrives. A primary concern for the LHC is the additional heat load due to the electron cloud that is deposited on the beam screen, a perforated tube inserted into the cold bore of the superconducting magnets in order to protect the cold bore from synchrotron radiation and ion bombardment [7]. The coefficient R designates the probability for an elastic reflection in the limit of zero primary energy (0 < R < 1)
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