In the first of our series of articles on work done during LS2, we focus on the second link in the accelerator chain, the PS Booster

The LS2 marathon has begun. In all the accelerators, teams have set about the tasks of maintaining or renovating numerous hardware components or replacing them with new and often innovative systems. Most of this major upgrade work is being done as part of the LHC Injectors Upgrade (LIU) project, which has been under preparation for several years and aims to increase the performance of the accelerators. The Engineering Department’s ACE group has been coordinating the schedule for all the installation work, with one coordinator per accelerator assigned to organising the master schedule and to liaising with the coordinators of each work package.

The PS Booster is to be completely transformed. When the new linear accelerator, Linac4, starts operating at the end of LS2, the PS Booster will receive protons at an energy of 160 MeV, compared with 50 MeV from the old Linac2. The injection system into the Booster therefore needs to be completely modified, especially as Linac4 will be accelerating H− ions (formed from a hydrogen atom and an additional electron). These ions will be stripped from their electrons by an ingenious injection system before being accelerated in the Booster up to 2 GeV, compared with 1.4 GeV in the past. In addition to the injection system upgrade, the radiofrequency acceleration and power supply systems will also be replaced, the magnets upgraded and the transfer line to the PS renovated.

David Hay is coordinating installation work at the PS Booster during LS2. “In actual fact, renovation work started as far back as 2016,” he explains, “with the civil-engineering work, cable removal and laying campaigns and the installation of new instrumentation.” In parallel, all the new equipment for high-intensity-beam operation was developed and manufactured, as part of the LIU project. A new building (245) has been constructed to house the Booster’s new power supply system, designed to cope with the higher energy of the accelerator. The power converters will supply power to the magnets with electrical intensities of 5500 amps, compared with 4000 amps previously. The new “POPS-B” power supply system was tested at the end of 2018 and successfully supplied the required level of power. This was an important milestone in the Booster’s performance upgrade.

The cable removal campaign has also begun. Another particularly tricky operation began this week with the dismantling of the equipment in the Booster’s injection zone. “Out of the 215 metres of beamlines of the PS Booster complex, 70 metres will need to be removed to make way for new injection and extraction equipment,” explains Wim Weterings of the TE-ABT group, who is supervising the work on the transfer lines. The equipment to be removed includes septum and kicker magnets, dipoles, quadrupoles and corrector magnets. Installation of the new systems should begin towards the end of the spring.

Some magnets will need to be replaced in the transfer lines as well as in the Booster ring. “We have to take out over 60 magnets. Most will be replaced with new magnets but some will be reconditioned,” explains Antony Newborough of the TE-MSC group, who is responsible for the Booster magnets. The heaviest weigh around 18 tonnes.

A new acceleration system has been developed for the PS Booster. It consists of new RF cavities based on a composite material (FineMet) assembled in three structures like the one above Image: Matthias Haase/CERN)

The radiofrequency acceleration system will be completely replaced. Since 2012, a new system based on cavities built using a composite magnetic material called FineMet has been developed in collaboration with Japanese institute KEK. Two cavities have been conclusively tested in situ over the course of several runs. The three structures, each containing eight cavities, are ready to be installed once the old cavities have been removed. A new electrical power system has also been developed. “From the end of February, we will be installing 24 racks containing 144 power converters as well as 18 racks containing the control modules in the surface building. This will take two months,” explains Matthias Haase of the BE-RF group, who is coordinating the work.

In addition to the work being performed at the heart of the accelerator, much is also being done on the infrastructures, including the replacement of the cooling system and the installation of new cooling towers.

The room housing the power converters and the control system for the PS Booster is completely empty during LS2. All cables running under the false floor are removed before installing the new power and control system (Image: Matthias Haase/CERN)

More pictures of the first dismantling of magnets in the PS Booster are available on CDS: