Update of the Linac4-PSB Transfer Line

The installation of Linac4 represents the first step of the upgrade plans of the CERN accelerator complex for the future in order to raise the available proton flux to attain amongst others the LHC ultimate luminosity. This linac is capable to accelerate H--ions from 45keV to 160MeV, which will be injected into the Proton Synchrotron Booster (PSB). The increase of energy from 50MeV (Linac2) to 160MeV (Linac4) allows to overcome the space charge limitations at the PSB injection, which is the main bottleneck towards higher beam brightness in the downstream accelerator chain. In order to preserve beam quality from the outlet of Linac4 to PSB injection the design of the transfer line becomes crucial. As the location of Linac4 was chosen in view of upgrade scenarios, the construction of a new transfer line is foreseen, see ref.[1] and ref.[2]. Here part of the Linac2-PSB transfer line will be re-used. In the new part of the transfer line the beam is horizontally and vertically adjusted towards the bending magnet BHZ20, which marks the separation point between the new and the old transfer line. Downstream BHZ20 the beam follows the Linac2-PSB transfer line up to the PSB injection. Due to the increased energy from 50MeV to 160MeV some elements of the existing transfer line have to be refurbished to fulfil the required performance. To achieve a PSB-acceptable energy spread the installation of a debuncher cavity is foreseen in the new transfer line part. As the Linac4-PSB injection scheme includes longitudinal phase space painting with an energy swing of ±1.2MeV within less than 40µs the tuning of the debuncher cavity phase within the same time interval as well as a good dispersion control are needed. The new layout is characterised by minimising of emittance growth, the adaption to the recent changes of the transfer line infrastructure and the efficient matching of longitudinal as well as transverse requirements of the PSB injection. With respect to the lattice layout of the transfer line that is presented in note AB-Note-2008-036-ABP the focusing strategy in the initial part is completely re-designed. This new focusing scheme results in a better beam quality. The debuncher cavity is shifted downstream from 34m to 44m, which leads to improved reduction of the energy spread at the injection point within the limitation of the PSB injection scheme. Furthermore, the six sets of transverse beam parameters defined for PSB injection can be matched with penalty functions better than 15%. This new layout allows beam transport from Linac4 to the PSB including dispersion control, loss management and matching to the PSB.