Accelerator and target news

The past year saw an extended maintenance shutdown for ISIS, from August 2010 to February 2011. The shutdown was necessary to replace a wide range of ageing ISIS equipment and components, many of which were installed over 25 years ago. Two major projects were carried out: refurbishment of part of the proton beamline for ISIS Target Station 1, and replacement of heavy-duty electrical cable for the accelerator magnets. In addition, some 700 smaller tasks were also completed: around 200 tasks on the accelerators, 200 on the neutron target systems and 300 on the neutron beam lines and instruments, including major rebuilds of Pearl and Polaris.

Refurbishment of the proton beamline to Target Station 1


After 25 years of being bombarded by high energy protons, the proton beam exit window in front of the neutron target in target station 1 had become weak. During the six month shutdown, nearly 60 people worked on the project to replace the window.

The refit was planned in great detail over several years since special long-reach tools, machines and shielding flasks had to be designed and constructed, movable thick steel shields had to be deployed, and rehearsals of the whole refurbishment were made using a full-scale mock-up of the work area. The project involved removing the layers of concrete and steel shielding above the proton beam, a 4-week task in its own right.

In addition to replacing the proton beam window, three new quadrupole magnets were also installed, replacing older magnets and providing additional control for the proton beam.

Target Station 1 proton beamline refurbishment

The team who worked on the Target Station 1 proton beamline refurbishment
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Second Target Station target


The long shut-down also saw replacement of the target in TS-2. A revised design with improved cooling based on experience of operating the target since TS-2 began running was installed. The new target was designed and manufactured within 8 months – a big achievement.

 

Rewiring the ISIS synchrotron


Also during the long shutdown, over 2km of heavy-duty power cables were replaced in the ISIS synchrotron accelerator. The cables deliver rapidly-varying currents up to 1000 amps to the bending magnets controlling the proton beam path.


A ring of 10 bending magnets in the ISIS synchrotron keeps the proton beam within the evacuated beam tube as it is accelerated. As the beam gets faster during acceleration, the current in the magnets is increased to give the larger and larger magnetic fields needed to keep the beam following the correct path.

The power cables for the magnets were originally installed in the 1980s. The cables were jointed, and over the past two years joints have begun to fail more and more frequently. To improve performance, the entire cable installation was replaced with single continuous cable runs – a job involving many weeks of specialised work removing heavy cables, each 4 cm in diameter.

Rewiring the ISIS synchtrotron

Adrian McFarland (ISIS) in the inner synchrotron during the recabling work.
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Synchrotron magnet replacement


From time to time the main bending (dipole) magnets in the ISIS synchrotron accelerator are replaced. This involves splitting a magnet in half and refitting new upper and lower coils as well as cleaning up the yoke and laminations.

Synchrotron magnet replacement

New extract and injection septum magnet busbar system for the ISIS synchrotron.
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