8 Accelerator Engineering and Technology: Accelerator Technology
479
Fig. 8.84 The stored energy (left) and the density of stored energy (right) are shown versus the
beam momentum for various accelerators. Filled symbols refer to proton, while open symbols
indicate electron/positron accelerators. ILC and CLIC are design studies
at the location of the smallest ring aperture, by design a collimator. In modern
proton colliders, these power losses must be controlled in the presence of superconducting magnets, placing high demands on the efficiency of collimators.
– Lepton storage rings (like LEP2) have additional power loss due to synchrotron
radiation [211]. The power loss can reach several MW, for example in LEP2
where 3% of the beam energy was lost per turn. Synchrotron radiation losses
are distributed over the length of the accelerator. Collimators intercept only part
of the synchrotron radiation, mainly at strategic locations at the end of the arcs or
around any experimental detectors.
– Linac-based accelerators (SNS, J-PARC, CLIC, ILC) do not store the beams but
regenerate them at 5–100 Hz, using each beam pulse only once [223, 227, 232].
Power loss can range from a few kW at SNS to a few 10 kW at the ILC (for a
0.1% loss per beam pulse). Losses can appear concentrated at one collimator.
It is seen that modern collimators must usually be designed for an impacting
power in the range from a few kW to 500 kW. Future projects must aim at designs
capable to cope with multi-MW levels. Depending on the choice of jaw material and
length only a fraction of the impacting beam power will remain in the collimator jaw,
the rest being sprayed downstream. A proper design of thermal heat flow, collimator
cooling and vacuum outgassing is essential.
8.8.2.2 Destructive Beam Densities
The transverse beam size σ z at collimator locations has decreased over the years,
either due to lower normalized emittances from injectors or due to the operation
at high beam energies (adiabatic emittance damping). This increases the energy
density in the beam:
ρ E = E stored /
πσ x σ y
(8.75)
479
Fig. 8.84 The stored energy (left) and the density of stored energy (right) are shown versus the
beam momentum for various accelerators. Filled symbols refer to proton, while open symbols
indicate electron/positron accelerators. ILC and CLIC are design studies
at the location of the smallest ring aperture, by design a collimator. In modern
proton colliders, these power losses must be controlled in the presence of superconducting magnets, placing high demands on the efficiency of collimators.
– Lepton storage rings (like LEP2) have additional power loss due to synchrotron
radiation [211]. The power loss can reach several MW, for example in LEP2
where 3% of the beam energy was lost per turn. Synchrotron radiation losses
are distributed over the length of the accelerator. Collimators intercept only part
of the synchrotron radiation, mainly at strategic locations at the end of the arcs or
around any experimental detectors.
– Linac-based accelerators (SNS, J-PARC, CLIC, ILC) do not store the beams but
regenerate them at 5–100 Hz, using each beam pulse only once [223, 227, 232].
Power loss can range from a few kW at SNS to a few 10 kW at the ILC (for a
0.1% loss per beam pulse). Losses can appear concentrated at one collimator.
It is seen that modern collimators must usually be designed for an impacting
power in the range from a few kW to 500 kW. Future projects must aim at designs
capable to cope with multi-MW levels. Depending on the choice of jaw material and
length only a fraction of the impacting beam power will remain in the collimator jaw,
the rest being sprayed downstream. A proper design of thermal heat flow, collimator
cooling and vacuum outgassing is essential.
8.8.2.2 Destructive Beam Densities
The transverse beam size σ z at collimator locations has decreased over the years,
either due to lower normalized emittances from injectors or due to the operation
at high beam energies (adiabatic emittance damping). This increases the energy
density in the beam:
ρ E = E stored /
πσ x σ y
(8.75)