Rejuvenating CERN's Accelerators
In the coming years and especially in 2005, CERN's accelerators are going to receive an extensive renovation programme to ensure they will perform reliably and effectively when the LHC comes into service.
When the LHC is commissioned it will rely on its injector complex to deliver beams at top performance and with high reliability. Thanks to a dedicated upgrade programme, the LHC injector complex has already demonstrated proton beam performances that are close to what the LHC will require. Additional upgrades are presently being implemented for ions.
However, the 45-year-old Proton Synchrotron (PS) and the 32-year-old PS Booster were offline respectively for two weeks in 2003 and for one week in 2004, disrupting physics work on several experiments. They were repaired, but they weren't the only occasions that the most senior accelerators of the injector complex have shown signs of their age. To ensure it is in good condition when the LHC is commissioned, the PS along with CERN's other accelerators in the LHC injector chain will benefit from an upgraded programme of âconsolidation'.
For the sake of saving resources for the LHC project, it was not possible to maintain the same level of maintenance for approximately the last decade. During that time, the emphasis changed from preventive maintenance to reactive maintenance, where items were repaired only when they failed.
Consolidation is the replacement of parts which are at the end of their useful life and the updating of obsolete components and systems. In order to carry out the upgraded consolidation programme, the accelerator complex requires a high level of resources with an annual material budget of about MCHF 8 .
The consolidation programme is intended to identify potential problems before operations are affected. Designing an effective programme is a challenge as everything in the accelerator has to be assessed. The risk of a given component failing, and the disruption it might cause, is determined for each system. Components that would cause the biggest problems are given priority in the schedule. However, no consolidation programme can ever be static and the accelerator teams have to react to changing circumstances, solving unexpected problems as they arise. One recent example was the failure of a brand new septum magnet (a vital component used to extract part of the beam while the other part is not perturbed and continues to circulate in the ring), which took the PS offline for several days but whose failure was unexpected.
The LHC injector complex is composed of the Linac2, the PS Booster, the PS and the Super Proton Synchrotron (SPS) delivering proton beams, and of the Linac3, LEIR, PS and the SPS delivering ion beams.
Not surprisingly, as it is the oldest accelerator in operation at CERN if not in the world, the components of the PS are high on the priority list for consolidation.
The Proton Synchrotron
The PS first accelerated a beam to full energy of 24 GeV on 24 November 1959. At the time, the PS used novel technology which proved to be very well chosen. It has been continually upgraded to provide higher beam intensity, which is now thousands of times greater than originally designed, and to accelerate various kinds of particles (protons, antiprotons, ions, electrons and positrons). However, it is still equipped with a large number of its original components.
Wear and tear in the PS results from a combination of the degradation of organic materials submitted to irradiation, and mechanical fatigue due to pulsed magnetic forces. Components affected include the main coil insulation, the insulation of the Pole Face Windings and the insulation of current leads. When these components fail, short circuits may damage the magnets, as it happened during the high voltage tests prior to start-up in spring 2003, when for the first time in their long career, two PS magnets and a bus bar connection failed, requiring a five-week repair programme (see Bulletin 19/2003).
These magnets were taken to the workshop in building 151 and renovated using spare components.
The repair shop
The current consolidation programme will allow the rejuvenation of the PS magnets as well as number of other critical components, making the best use of the unique opportunity provided by the long shut-down starting in November 2004 and continuing throughout 2005. During this period it is hoped to renovate about 50% of the PS magnets, taking full advantage of the long period for radioactivity to decline and thus minimize the dose taken by the experts during repair.
After 45 years of very successful operation, and thanks to a reinforced consolidation programme, the PS will pursue its success story at least for the whole lifetime of the LHC, to 2020 and possibly beyond.
