8 Accelerator Engineering and Technology: Accelerator Technology
435
8.5.4.2 Vacuum Instrumentation
8.5.4.2.1 Pressure Sensors
Similar to the pumps, the evolution of the pressure sensors is stimulated by the
needs of the industry and the tendency is to use pressure sensors with electronics on
their heads. All types of pressure sensors are now available in catalogues covering
the range of pressure from several atmospheres (10 6 Pa) down to UHV pressures
(10 −10 Pa). These products are cheap, reliable and easy to maintain.
However, their use in particle accelerators is also compromised by the inherent
radiation. An alternative are the so-called passive gauges with the electronics
decoupled from the pressure sensor. The existing sensors can be placed far away,
up to 2 km, from their controllers. It should be noted that the installation of
appropriate cables is an important issue to allow use of the sensors up to their
design specifications. Special attention has to be taken while laying the cables,
to avoid electromagnetic incompatibility and interference (EMI) perturbations; it
is recommended to lay these cables in special cable trays or with instrumentation
cables and to pay special attention to cable shielding and grounding loops.
The ion pumps are also often used as pressure indicators since their discharge
current is proportional to the pressure. Modern controls electronics allow a fast
conversion of the currents into pressures. The stability of the discharge current
explains why these signals are used as pressure interlocks.
8.5.4.2.2 Residual Gas Analyzers (RGA)
The residual gas analysers are of primary importance to understand the beam-gas
scattering since, as mentioned earlier, the ionisation cross-section varies with the gas
species. Therefore, while operating an accelerator with beams, knowing the residual
gas composition can allow calculating the beam lifetime and predicting potential
limitations.
As the modern accelerators require more and more UHV conditions to operate,
the RGAs must provide partial pressure resolutions in the low 10 −11 Pa range to
provide useful information. This type of residual gas analyser is available off-theshelf, but in many cases, the electronics is attached to the head or placed at a few
meters. This limitation still exists and the demand being very small, most of the
suppliers do not plan to modify the position of the electronics thereby limiting the
use of RGA to radiation free environment.
8.5.4.3 Vacuum Sectorisation
The sectorisation of the beam vacuum system results from the combination of various constraints, the major being: venting and bake-out requirements, conditioning
requirements (RF and HV devices), protection of fragile and complex systems
435
8.5.4.2 Vacuum Instrumentation
8.5.4.2.1 Pressure Sensors
Similar to the pumps, the evolution of the pressure sensors is stimulated by the
needs of the industry and the tendency is to use pressure sensors with electronics on
their heads. All types of pressure sensors are now available in catalogues covering
the range of pressure from several atmospheres (10 6 Pa) down to UHV pressures
(10 −10 Pa). These products are cheap, reliable and easy to maintain.
However, their use in particle accelerators is also compromised by the inherent
radiation. An alternative are the so-called passive gauges with the electronics
decoupled from the pressure sensor. The existing sensors can be placed far away,
up to 2 km, from their controllers. It should be noted that the installation of
appropriate cables is an important issue to allow use of the sensors up to their
design specifications. Special attention has to be taken while laying the cables,
to avoid electromagnetic incompatibility and interference (EMI) perturbations; it
is recommended to lay these cables in special cable trays or with instrumentation
cables and to pay special attention to cable shielding and grounding loops.
The ion pumps are also often used as pressure indicators since their discharge
current is proportional to the pressure. Modern controls electronics allow a fast
conversion of the currents into pressures. The stability of the discharge current
explains why these signals are used as pressure interlocks.
8.5.4.2.2 Residual Gas Analyzers (RGA)
The residual gas analysers are of primary importance to understand the beam-gas
scattering since, as mentioned earlier, the ionisation cross-section varies with the gas
species. Therefore, while operating an accelerator with beams, knowing the residual
gas composition can allow calculating the beam lifetime and predicting potential
limitations.
As the modern accelerators require more and more UHV conditions to operate,
the RGAs must provide partial pressure resolutions in the low 10 −11 Pa range to
provide useful information. This type of residual gas analyser is available off-theshelf, but in many cases, the electronics is attached to the head or placed at a few
meters. This limitation still exists and the demand being very small, most of the
suppliers do not plan to modify the position of the electronics thereby limiting the
use of RGA to radiation free environment.
8.5.4.3 Vacuum Sectorisation
The sectorisation of the beam vacuum system results from the combination of various constraints, the major being: venting and bake-out requirements, conditioning
requirements (RF and HV devices), protection of fragile and complex systems