Uncontrolled Longitudinal Emittance Blow-Up during rf Manipulations in the CERN PS

A Lasheen,G Favia,H Damerau

doi:10.1088/1742-6596/1067/6/062018

Abstract

The CERN Proton Synchrotron (PS) determines the basic bunch spacing for the Large Hadron Collider (LHC) by means of rf manipulations. Several rf systems in a frequency range from 2.8 MHz to 200 MHz are available for beam acceleration and manipulations. Each of the six bunches injected from the PS Booster is split in several steps into 12 bunches spaced by 25 ns, yielding a batch of 72 bunches at transfer to the Super Proton Synchrotron (SPS). In the framework of the LHC Injector Upgrade (LIU) project the bunch intensity must be doubled. However, with most of the planned upgrades already in place this intensity has not yet been achieved due to collective effects. One of them is uncontrolled longitudinal emittance blowup during the bunch splittings. In this contribution, measurements of the blow-up during the splitting process are presented and compared with particle simulations using the present PS impedance model. Beam-based measurements of the impedances of the rf cavities have been performed. They revealed that to reproduce the instability an additional impedance source is required in the PS impedance model.

Highlights

One of the requirements of the High Luminosity-Large Hadron Collider (LHC) (HL-LHC) project at CERN is to double the beam intensity
One of the requirements of the High Luminosity-LHC (HL-LHC) project at CERN is to double the beam intensity. This target is challenging for the injectors, which are being upgraded in the framework of the LHC Injector Upgrade (LIU) project
The beam intensity extracted from the Proton Synchrotron (PS) for the LHC is Nb = 1.3 × 1011 protons per bunch (p/b), and the LIU target is Nb = 2.6 × 1011 p/b with the same longitudinal emittance

Summary

Introduction

One of the requirements of the High Luminosity-LHC (HL-LHC) project at CERN is to double the beam intensity. Several rf cavities of different harmonics, h, are available to perform rf manipulations like bunch splitting or merging, batch compression and controlled longitudinal emittance blow-up. During Machine Development (MD) sessions, a perturbation of the bunch profile was observed when the third 80 MHz cavity gap was opened, as shown in Fig. 1 (right) [3].

Results

Conclusion