9 Accelerator Operations
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energy or intensity increase above damage level, the interlocks are automatically
enabled.
9.9.8 Beam Instrumentation for Machine Protection
Beam instrumentation plays an important role for machine protection, and is used
to monitor beam parameters and stop beam operation if a parameter is outside a
predefined range. If machine protection relies on the correct operation of beam
instruments, failures in beam instrumentation sub-systems need to be considered.
9.9.8.1 Beam Loss Monitors—BLM
BLMs are used for monitoring beam losses and can clearly play an important role in
machine protection. In simple terms the BLMs measure localized beam losses along
the accelerator and stop beam operation in case losses the losses become too high.
It is important that the monitors cover the entire accelerator and there is no region
with potential for losses without BLM coverage.
The monitors can be fast, for example, the LHC BLMs operate on a 40 μs timescale. The BLM system should be designed so that it can trigger a beam dump and
stop operation before beam losses on this scale can damage equipment.
Failure cases for the system might include defective BLMs providing no or too
low readings and therefore not providing a signal even in case of high beam losses;
and the thresholds could be set incorrectly. The former can be caught via rigorous
unit testing, the latter by strict and rigorous threshold management.
9.9.8.2 Beam Position Monitors—BPM
BPMs coupled with appropriate orbit or trajectory correction can ensure that the
beam is in the correct place in respect to the aperture. This position would normal
be around the centre of the beam pipe but there are many exceptions, for example
during extraction where a closed orbit bump is applied to position the beam close
to a septum magnet. BPMs can monitor the amplitude of such bumps and are
effectively redundant monitors of the magnet current in the closed orbit dipoles.
One possible issues is the presence of constant offset in BPM readings which can
be independent of the beam position. If a closed orbit feedback system is used, the
feedback tries to correct an erroneous position. A closed-orbit bump can develop
and, in the worst case, the beam touches the aperture. Even if the protection systems
work correctly and the beam is dumped there is some risk—for example, the beam
dump kicker might push the trajectories of part of the beam to the aperture.
577
energy or intensity increase above damage level, the interlocks are automatically
enabled.
9.9.8 Beam Instrumentation for Machine Protection
Beam instrumentation plays an important role for machine protection, and is used
to monitor beam parameters and stop beam operation if a parameter is outside a
predefined range. If machine protection relies on the correct operation of beam
instruments, failures in beam instrumentation sub-systems need to be considered.
9.9.8.1 Beam Loss Monitors—BLM
BLMs are used for monitoring beam losses and can clearly play an important role in
machine protection. In simple terms the BLMs measure localized beam losses along
the accelerator and stop beam operation in case losses the losses become too high.
It is important that the monitors cover the entire accelerator and there is no region
with potential for losses without BLM coverage.
The monitors can be fast, for example, the LHC BLMs operate on a 40 μs timescale. The BLM system should be designed so that it can trigger a beam dump and
stop operation before beam losses on this scale can damage equipment.
Failure cases for the system might include defective BLMs providing no or too
low readings and therefore not providing a signal even in case of high beam losses;
and the thresholds could be set incorrectly. The former can be caught via rigorous
unit testing, the latter by strict and rigorous threshold management.
9.9.8.2 Beam Position Monitors—BPM
BPMs coupled with appropriate orbit or trajectory correction can ensure that the
beam is in the correct place in respect to the aperture. This position would normal
be around the centre of the beam pipe but there are many exceptions, for example
during extraction where a closed orbit bump is applied to position the beam close
to a septum magnet. BPMs can monitor the amplitude of such bumps and are
effectively redundant monitors of the magnet current in the closed orbit dipoles.
One possible issues is the presence of constant offset in BPM readings which can
be independent of the beam position. If a closed orbit feedback system is used, the
feedback tries to correct an erroneous position. A closed-orbit bump can develop
and, in the worst case, the beam touches the aperture. Even if the protection systems
work correctly and the beam is dumped there is some risk—for example, the beam
dump kicker might push the trajectories of part of the beam to the aperture.