Vacuum
ISIS has been operational for more than 30 years . Image source : STFC
The second Target Station ( TS2 ) was added in August 2008 . Image source : STFC
The section is also responsible for the manufacture of extremely delicate stripping foils used in the synchrotron and carries out detailed testing of materials for vacuum compatibility . We also test all new vacuum equipment prior to installation on the machine or instruments .
The vast majority of the ISIS machine operates in a high vacuum environment . Stainless steel and ceramic vessels are used in these areas , with aluminium or indium seals used to join the vessels together .
In terms of vacuum equipment , on just the machine alone there are a total of 25 turbo pumps ( with pumping speeds ranging from 300 to 2000l / s ) in the linac and 54 ion pumps ( 400l / s triodes ) in the synchrotron and beam transfer lines . Special RF screened ( to minimise beam disturbance ) and all-metal gate valves are used to isolate parts of the machine . Residual gas analysers are used to monitor vacuum systems in the linac and also the gas composition in each of the two target stations .
All this equipment is operated and monitored using control systems designed and maintained by in house support staff . As anyone responsible for maintaining vacuum systems that operate 24 / 7 will know , regular maintenance is essential for ensuring long term reliability . Hence on ISIS approximately every four years the whole facility undergoes a scheduled six month or “ long shutdown ”, in addition to shorter ( 10-15 days ) shutdowns that occur after every six to eight weeks of operation . These long shutdowns are not just an opportunity to carry out general maintenance on vacuum equipment such as pumps and gauges but they are also a chance to carry out major improvements and upgrades to ensure ISIS remains at the cutting edge of science and technology .
Detailed planning and consultation takes place in the months prior to a long shutdown to ensure new equipment is installed with minimal disruption . In fact a full size mock-up of part of the working area was constructed to help staff get to grips with the space constraints that they could well find themselves working in .
The last long shutdown on ISIS occurred between August 2014 and February 2015 . During this period a section of vacuum beampipe approximately 12m in length on both sides of the intermediate target ( where the muons are created ) was replaced . At the same time eight new quadrupole magnets were fitted , as the previous ones ( some of which were second-hand when installed in 1987 ) were approaching the end of their useful lifetime . As part of this upgrade , new more reliable beam positioning monitors were also installed to minimise beam losses .
Following a detailed in-house review , the thin aluminium window that had previously separated the muon instruments from the intermediate target was also removed . Removal of this window along with further upgrades to the remaining magnets and vacuum pipework planned over the next SIX months are likely to result in at least a two-fold increase in the overall flux for the muon instruments .
During the long shutdown work also continued on the installation of two new instruments , IMAT and ZOOM , on TS2 .
At almost 50m 3 in volume the ZOOM vacuum tank is one of the largest on ISIS and was manufactured in two parts that were then welded together on site before being leak tested . IMAT has the longest vacuum guide section ( almost 46m ) of all instruments on ISIS . Both of these instruments will undergo detailed commissioned in preparation for user experiments later in the year . ( Further information about these four new instruments new can be found on the website www . isis . stfc . ac . uk / about-isis / target-station-2 /).
One of the biggest challenges of working on ISIS is pumping down large vacuum vessels to operational levels quickly . As these systems were not designed to be baked out , outgassing particularly from water vapour can sometimes be a major problem . Not surprisingly then top of my wishlist would be a compact , dry , air cooled vacuum pump that can pump at speeds of at least 100m 3 / h ( at atmospheric pressure ) and that can deal effectively with water vapour .
With more instruments to be installed on TS2 and further vacuum upgrades planned throughout the facility , there will be many new opportunities and challenges ahead . Indeed the knowledge and experience gained over 30 years of operation by ISIS staff will also be important in the design of Europe ’ s newest accelerator-based neutron source the European Spallation Source under construction in Sweden , in which the UK is a major contributor .
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