9 Accelerator Operations
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material that can be vaporised, melt, deform or lose its mechanical properties,
depending on the material and the beam impact.
There is already some risk of damage to sensitive equipment from an energy
deposition of some 10 kJ for a beam impact on the time scale of a few milliseconds.
The risk of damage to equipment from losses in the mega-Joule regime is enormous.
Equipment becomes activated due to beam losses. Rigorous radiation protection
measures are required and acceptable exposure limits must be clearly established.
For potential exposure to higher rates one possible approach is the ALARA principle
which aims to keep the exposure of personnel to radiation “As Low As Reasonably
Achievable”. Cool-down times might be required to respect this principle with
knock on costs to operational availability.
For accelerators with superconducting magnets there is a specific problem—
even with beam loss much below the damage threshold superconducting magnets
may quench due to the temperature increase induced by beam loss. In the case of a
quench, beam operation is interrupted leading to downtime for recovery. To avoid
beam induced quenches, beam losses are monitored and beam operation is aborted
if a predefined threshold is exceeded. Since the damage threshold is well above
the quench threshold, this strategy also protects the superconducting magnets from
damage.
There is no simple expression for the energy deposition of high energy particles,
since this depends on the particle type, the momentum, beam parameters and
material parameters (atomic number, density, specific heat). Programs such as
FLUKA [103], MARS [104] or [105] are used to estimate energy deposition as
well as the activation of the exposed material.
9.9.3 Time Constants for Beam Losses
Potential beam losses scenarios can be broken down according to the time scale of
the losses. Monitoring and reaction to losses must, of course, act at the appropriate
time scale.
9.9.3.1 Ultra Fast Beam Losses
Sources of failures that lead to a beam loss within very short time, typically in the
range of ns to μs are:
• failures of kicker magnets (during injection, at extraction, or during the use of
special kicker magnets used for beam diagnostics);
• failure during beam transfer via transfer lines between different accelerators or
from the accelerator to a target station.
573
material that can be vaporised, melt, deform or lose its mechanical properties,
depending on the material and the beam impact.
There is already some risk of damage to sensitive equipment from an energy
deposition of some 10 kJ for a beam impact on the time scale of a few milliseconds.
The risk of damage to equipment from losses in the mega-Joule regime is enormous.
Equipment becomes activated due to beam losses. Rigorous radiation protection
measures are required and acceptable exposure limits must be clearly established.
For potential exposure to higher rates one possible approach is the ALARA principle
which aims to keep the exposure of personnel to radiation “As Low As Reasonably
Achievable”. Cool-down times might be required to respect this principle with
knock on costs to operational availability.
For accelerators with superconducting magnets there is a specific problem—
even with beam loss much below the damage threshold superconducting magnets
may quench due to the temperature increase induced by beam loss. In the case of a
quench, beam operation is interrupted leading to downtime for recovery. To avoid
beam induced quenches, beam losses are monitored and beam operation is aborted
if a predefined threshold is exceeded. Since the damage threshold is well above
the quench threshold, this strategy also protects the superconducting magnets from
damage.
There is no simple expression for the energy deposition of high energy particles,
since this depends on the particle type, the momentum, beam parameters and
material parameters (atomic number, density, specific heat). Programs such as
FLUKA [103], MARS [104] or [105] are used to estimate energy deposition as
well as the activation of the exposed material.
9.9.3 Time Constants for Beam Losses
Potential beam losses scenarios can be broken down according to the time scale of
the losses. Monitoring and reaction to losses must, of course, act at the appropriate
time scale.
9.9.3.1 Ultra Fast Beam Losses
Sources of failures that lead to a beam loss within very short time, typically in the
range of ns to μs are:
• failures of kicker magnets (during injection, at extraction, or during the use of
special kicker magnets used for beam diagnostics);
• failure during beam transfer via transfer lines between different accelerators or
from the accelerator to a target station.