ISIS has a proton accelerator system which produces pulses of protons at extremely high speeds and fires them towards a tungsten target, generating neutrons through a process called spallation. This takes place in the Target Stations and at the heart of the Target Station is the TRaM, the Target, Reflector and Moderators. The team responsible for work to the TRaM is the Target Operations team, who rely on a remote handling set up to carry out this work.
When neutrons are emitted from the target, their energies are in the order of 1 MeV (mega-electron volt), but the instruments require neutrons with much lower energies, in the meV to eV region (milli-electron volt to electron volt). To achieve this reduction in energy, the target is surrounded by moderators. Within the moderators, collisions with hydrogen nuclei reduce the energy of the neutrons. The moderator is surrounded by a target reflector which returns neutrons that have attempted to scatter out of the moderators.
Target Station 2 has two moderators. A solid methane moderator and a liquid hydrogen moderator. The solid methane moderator is replaced every 3-6 months, while the hydrogen moderator is only replaced when there is a scientific need to do so. This January shutdown, the moderators were replaced, which required pipes, valves and cabling to be disconnected and then the moderator to be craned out of position and cropped before it is stored for disposal, all carried out by our Target Operations team. The current moderator in TS2 had not been replaced in 9 years, so this is a significant event.
The TRaM, seen through the lead-glass window in the remote handling Cell.
The Target Operations team’s work is made even more challenging as it needs to be done by remote handling. Due to high levels of radiation, the TRaM is shielded by steel and concrete. There is a very thick (1.2m) lead-glass window that the team can view the TRaM through, which, combined with the cameras set up in the TRaM are the only way the team can see what they are doing. The remote handling set up consists of mechanical arms controlled from the other side of the window. As anyone who has lost on a claw arcade game will tell you, it's not as easy as it looks. The arms require a lot of physical effort to move, and it takes high levels of patience and concentration to perform tasks that require a lot of dexterity. A task that might take 45 minutes using one’s hands can take the team around 3 days to complete via remote handling- and that’s if there are no complications.
The team have limited view of the TRaM through the window, so they also use cameras to see what they are doing.
During periods of shutdown, when the beam is off, the team operate in shifts, so work can take place from 6am to 10pm, often 7 days a week. They work hard to ensure that any work to the TRaM is complete in time for the planned beam-on date. During cycle, if issues arise, the team have been known to devote up to 24hrs a day to help restore the beam as quickly as possible. They are always looking for ways to refine their techniques and improve design to boost efficiency and reduce waste, recently changing the door seal to an aluminum ring that can be reused. Investigations are also being carried out to improve the target design. Currently the target is replaced every 2 years, but they are hoping to extend this lifetime by cutting open used targets to look for causes of failure that can be overcome in future designs.
The work that the Target Operations team carries out is unique, and hugely important to the running of ISIS. There is a strong sense of camaraderie amongst the team, who take immense pride in their work and clearly love what they do. “I’m lucky enough to have found a job that I love where it doesn't feel like work!” says Julius Bullock, Isis Target Operations Section Leader which he attributes to the amazing teams at ISIS.
