Vacuum Technology and Vacuum Design Handbook for Accelerator ...

Chapter 2
Design Criteria, Information and Philosophies
for Vacuum Systems used in the Accelerator Area
Overview
In an accelerator system ion beams are transported from ion sources through to end stations (or
detectors) through vacuum space maintained inside of beam tubes (lines). The relatively low
number of gas molecules in the vacuum ensures a higher mean free path for the accelerated ions and
hence less loss of ions through collision which is crucial especially for AMS measurements when
counting a very small number of ions. A high vacuum also minimises the formation of plasmas in an
electric field at high voltages which can avalanche into spark breakdown damaging sensitive
equipment.
The vacuum systems used in the accelerator area are designed to be fail-safe to protect people and
equipment. A very high proportion of problems with vacuum systems relate to, seals leaking on first
use, being incorrectly mounted or failing due to aging ‘o’ rings. Other problems, however less
frequent, include mechanical damage to sealing surfaces or fatigued parts such as bellows. The
problems are all characterised by a poor vacuum or a previously steady vacuum that begins
degrading slowly as observed during the operation of the vacuum system over its life time. The
remaining problems are due to poor welds or vacuum fittings breaking. Poor welds are usually
found during the initial helium leak test. They are remedied by either removing and re-welding the
section or using a commercial vacuum epoxy. The choice is dependant on whether the weld is on a
structural component or just a seal. Broken vacuum fittings are replaced or repaired.
Within the accelerator area,
physicists work directly with
technicians who apply broad
knowledge and experience in
vacuum technology to develop
their concepts for use in the
accelerator environment. This mix
has been successful for 50 years.
However not all designs are
completed in the accelerator area.
There are cases where commercial
projects call for a more production
based design or designs of
chambers with complex noncylindrical
shapes. These may go
to the ANSTO drawing office for
completion or a specialist vacuum
design company.
Fig 1. ANSTO designed and developed beam lines on the
STAR accelerator in building 22
It is not possible and often not necessary to standardise the design requirements for all components
used in the accelerator area so the following information is intended to help designers of vacuum
equipment to comply with accelerator specific and Australian standards. As of 2011, there are no
known commercial workshops in Australia who specialise in the production of vacuum vessels.
Local representatives from vacuum suppliers can provide access to overseas specialist workshops.
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