Vacuum Technology and Vacuum Design Handbook for Accelerator ...

The accelerator beam lines are divided into stand alone vacuum systems but in essence function as
one. Each system can impact on a neighbouring system if things go wrong. In the case of end
stations which cycle up and down in pressure more than any other devices an operator must be
100% sure of the pump down sequence in order to avoid damaging, pumps, samples, high voltage
devices, detectors, etc. It is possible to shut down the accelerators as well. Most sections of the
accelerator vacuum systems are interlocked to isolate a pressure surge to small area. Beam line
vacuum systems are design so that both the vacuum pump and the beam line are isolated via gate
valves. This is a typical arrangement for endstations as well.
The following must be read remembering that all 3 processes work in a cyclic fashion in a
continuous loop.
4.4 Operational Protocols
Key vacuum systems operate continuously, 24 hours per day, seven days per week. There are
several vacuum systems that are cycled on and off as usage demands. All vacuum systems have one
or more high vacuum gauges, some of which are interlocked to make the systems fail-safe. Any
slow leaks or major catastrophic failures will close valves and isolate the system. In the few cases
where no interlocks are used, a catastrophic failure will result in the high vacuum pump shutting
down.
• For a turbo pump, as the pressure rises the gas load on the pump will cause the pump to draw
more current to maintain it’s speed. It will eventually fail when the current trip level is
reached in the controller.
• For a cryopump, as the pressure rises the inflowing gas will condense or freeze onto the in
the pump until it begins to warm up. Eventually there will be a thermal trip activated o the
compressor which will shut is down. In both cases it is fail-safe.
As part of the accelerator’s maintenance system, daily monitoring of all vacuum pressures is carried
out. Where a pressure is seen to rise by a few percent without a particular reason, further monitoring
will occur and corrective action started. Instantaneous failures are dealt with immediately. All
observations and whether any maintenance carried out is noted on the maintenance log.
Where a vacuum system is isolated for service or where it has failed the appropriate tags are placed
on the power leads.
Unattended out of hour’s operation notification is not normally used as vacuum systems run
continuously.
4.5 Pump down
General
Pump down time is when most mistakes are made and significant time lost. Before a pump down
begins the operator must ensure that all seals that were disturbed had been cleaned and replaced if
damaged. The system must then be sealed ready for pump down and the roughing-out valve on the
rough-out port, closed.
If a dry pump is to be used, such as a scroll pump, for rough-out then the tube is connected to the
pumping port. If an oil vane rotary pump is used then ensure the cold trap has been filled
beforehand.
Rough-out
Start the roughing pump and allow it to reach base vacuum. This is your first indicator of whether
you have a leak in the system being pumped and when you have reached the pumping limit of the
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