6 Design and Principles of Synchrotrons and Circular Colliders
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energy beams) to deflect the beam into or out of the accelerator aperture, and
frequently also a closed orbit bump to approach the septum and reduce the required
kicker strength. For these single-turn methods, the beam losses can be very low,
and the emittance dilution associated with the injection or extraction can be very
small, defined by the delivery precision, the optics mismatch, the kicker flat top
ripple and septum stability. For both injection and extraction, the circulating beam
can be adversely affected by septum stray fields penetrating into the circulating
beam region and by the kicker field rise time which can overlap temporally with
circulating bunches. Injecting a bunched beam into another accelerator also requires
that the momentum spread and phase be matched to the RF bucket, and that the RF
system can accept the transient beam loading which arises from the sudden change
in beam intensity.
Multiple-turn injection is used to fill the circumference of a receiving accelerator
and to accumulate bunch intensity. A wide variety of multiple-turn injection and
extraction schemes exist, and these can be very different for lepton and hadron
machines. Lepton injection schemes can take advantage of synchrotron radiation
damping to achieve high beam brightness, while for hadron machines space charge
effects dominate, especially at low energy. High brightness proton injection can
make use of phase-space “painting” to precisely tailor the transverse and longitudinal distributions, particularly with H − charge exchange injection or slip stacking;
while resonant multiple-turn extraction schemes have been developed to provide
quasi-continuous particle fluxes for periods which range from milliseconds to hours.
The additional hardware systems required for these more advanced injection and
extraction techniques include multiple RF systems, programmed fast closed-orbit
bumps, stripping foils and non-linear lattice elements.
Overall, injection and extraction techniques share many similarities and hardware
requirements [8]: one important difference between them is that extraction is usually
at higher beam rigidity, which implies less effect from space charge and also
stronger and hence longer deflecting systems, which can have a significant effect
on lattice and insertion design [9–11].
6.3.1 Fast Injection
Fast injection [12–14] is typically used to fill another machine with bunch-to-bucket
transfer, or to fill a collider over several injections with ‘boxcar’ stacking, where
bunches or trains of bunches are added sequentially like boxcars (wagons) to a
train. The system design depends critically on the aperture needed for the beam,
and the kicker rise time, fall time and flat top duration. Very fast kicker rise times
are often required to maximize the amount of beam which can be injected, especially
in machines with small circumferences, since the kicker rise and fall times must be
significantly shorter than the revolution time.
223
energy beams) to deflect the beam into or out of the accelerator aperture, and
frequently also a closed orbit bump to approach the septum and reduce the required
kicker strength. For these single-turn methods, the beam losses can be very low,
and the emittance dilution associated with the injection or extraction can be very
small, defined by the delivery precision, the optics mismatch, the kicker flat top
ripple and septum stability. For both injection and extraction, the circulating beam
can be adversely affected by septum stray fields penetrating into the circulating
beam region and by the kicker field rise time which can overlap temporally with
circulating bunches. Injecting a bunched beam into another accelerator also requires
that the momentum spread and phase be matched to the RF bucket, and that the RF
system can accept the transient beam loading which arises from the sudden change
in beam intensity.
Multiple-turn injection is used to fill the circumference of a receiving accelerator
and to accumulate bunch intensity. A wide variety of multiple-turn injection and
extraction schemes exist, and these can be very different for lepton and hadron
machines. Lepton injection schemes can take advantage of synchrotron radiation
damping to achieve high beam brightness, while for hadron machines space charge
effects dominate, especially at low energy. High brightness proton injection can
make use of phase-space “painting” to precisely tailor the transverse and longitudinal distributions, particularly with H − charge exchange injection or slip stacking;
while resonant multiple-turn extraction schemes have been developed to provide
quasi-continuous particle fluxes for periods which range from milliseconds to hours.
The additional hardware systems required for these more advanced injection and
extraction techniques include multiple RF systems, programmed fast closed-orbit
bumps, stripping foils and non-linear lattice elements.
Overall, injection and extraction techniques share many similarities and hardware
requirements [8]: one important difference between them is that extraction is usually
at higher beam rigidity, which implies less effect from space charge and also
stronger and hence longer deflecting systems, which can have a significant effect
on lattice and insertion design [9–11].
6.3.1 Fast Injection
Fast injection [12–14] is typically used to fill another machine with bunch-to-bucket
transfer, or to fill a collider over several injections with ‘boxcar’ stacking, where
bunches or trains of bunches are added sequentially like boxcars (wagons) to a
train. The system design depends critically on the aperture needed for the beam,
and the kicker rise time, fall time and flat top duration. Very fast kicker rise times
are often required to maximize the amount of beam which can be injected, especially
in machines with small circumferences, since the kicker rise and fall times must be
significantly shorter than the revolution time.