LHC luminosity upgrade with large Piwinski angle scheme: a recent look

TL;DR

This paper reevaluates the Large Piwinski Angle scheme for LHC luminosity upgrades, considering recent operational data, beam dynamics, and injector performance to propose new parameters and necessary upgrades.

Contribution

It provides a revised set of parameters and luminosity estimates for the LHC upgrade using the large Piwinski angle scheme based on recent beam studies.

Findings

Beam-beam tune shift exceeds initial design expectations.

New parameters suggest feasible luminosity upgrade.

Injector performance impacts scheme viability.

Abstract

Luminosity upgrade at the LHC collider using longitudinally flat bunches in combination with the large crossing angle (large Piwinski angle scheme) is being studied with renewed interest in recent years. By design, the total beam-beam tune shift at the LHC is less than 0.015 for two interaction points together. But the 2010-11 3.5 TeV collider operation and dedicated studies indicated that the beam-beam tune shift is >0.015 per interaction point. In view of this development we have revisited the requirements for the Large Piwinski Angle scheme at the LHC. In this paper we present a new set of parameters and luminosity calculations for the desired upgrade by investigating 1) current performance of the LHC injectors, 2) e-cloud issues on nearly flat bunches and 3) realistic beam particle distributions from longitudinal beam dynamics simulations. We also make some remarks on the needed upgrades on the LHC injector accelerators.