324
J. Seeman et al.
As the beam stability requirement is quite stringent and typically 10% of the
beam size, tight jitter tolerances for the rings extraction kickers are imposed, down
to a few10 −4 . Especially for the bunch-by-bunch extraction scheme of ILC, the
kicker rise time of a few ns, is extremely challenging. An ILC extraction experiment
using a prototype strip-line kicker was carried out at KEK-ATF [108]. It achieved
multi-bunch beam extraction with 5.6 ns bunch spacing. The angle jitter of a single
bunch beam was reduced to 3.5 × 10 −4 , using a double kicker system. For CLIC,
a stripline with an ultra-stable inductive adder as power source is being currently
tested at ALBA synchrotron [109].
7.8 Recirculated Linacs and Energy Recovery
S. A. Bogacz · G. A. Krafft
Linear accelerators provide superb beam quality as defined by the sources, but they
are current-limited due to the high cost of their RF drive. Circular accelerators, by
contrast, offer high average beam current and exhibit high electrical efficiency (and
associated cost reductions) because of the limited required investment in RF power.
However, effects such as quantum excitation (incoherent synchrotron radiation)
or space charge limit their beam quality. On the other hand, rings typically only
come to equilibrium after many hundreds or thousands of turns, which significantly
degrades beam quality (emittance, momentum spread, etc.).
Recirculated Linear Accelerators (RLAs) have several advantages that support
electron beam parameters outside of the scope of the traditional ring accelerators or
linacs [110]. Synchrotron radiation effects, as in electron storage rings, do not limit
beam emittances and pulse lengths emerging from an RLA. The beam is circulated
only a modest number of times, so the impacts of the degrading effects are then
limited, and the beam quality may be much higher than the equilibrium beam quality
inherent for rings.
Going a step further, in the Energy-Recovered Linac (ERL), the full-energy
beam is returned to the accelerating structure out of phase with respect to the
accelerating field after being used (collides, produces synchrotron radiation, drives
a specific reaction, etc.). The beam is decelerated, returning the RF power in the
beam to the accelerating structure, making this RF power available to accelerate
a subsequent beam. The resulting system retains the excellent beam quality of
a conventional linac—and, because of the recovery of significant levels of RF
power—can provide high average beam current at excellent electrical efficiency
and lower associated cost. The ERL concept is quite attractive because it provides
linac-quality/brightness beam at storage ring beam powers. With the advent of
operational ERLs, it may be possible to push average currents to levels approaching
the best lepton storage rings in existence as of 2019. Furthermore, the production of
high beam power with reduced RF drive represents improved electrical efficiency,
introducing ‘green technology’ with significant cost reductions. Energy recovery
J. Seeman et al.
As the beam stability requirement is quite stringent and typically 10% of the
beam size, tight jitter tolerances for the rings extraction kickers are imposed, down
to a few10 −4 . Especially for the bunch-by-bunch extraction scheme of ILC, the
kicker rise time of a few ns, is extremely challenging. An ILC extraction experiment
using a prototype strip-line kicker was carried out at KEK-ATF [108]. It achieved
multi-bunch beam extraction with 5.6 ns bunch spacing. The angle jitter of a single
bunch beam was reduced to 3.5 × 10 −4 , using a double kicker system. For CLIC,
a stripline with an ultra-stable inductive adder as power source is being currently
tested at ALBA synchrotron [109].
7.8 Recirculated Linacs and Energy Recovery
S. A. Bogacz · G. A. Krafft
Linear accelerators provide superb beam quality as defined by the sources, but they
are current-limited due to the high cost of their RF drive. Circular accelerators, by
contrast, offer high average beam current and exhibit high electrical efficiency (and
associated cost reductions) because of the limited required investment in RF power.
However, effects such as quantum excitation (incoherent synchrotron radiation)
or space charge limit their beam quality. On the other hand, rings typically only
come to equilibrium after many hundreds or thousands of turns, which significantly
degrades beam quality (emittance, momentum spread, etc.).
Recirculated Linear Accelerators (RLAs) have several advantages that support
electron beam parameters outside of the scope of the traditional ring accelerators or
linacs [110]. Synchrotron radiation effects, as in electron storage rings, do not limit
beam emittances and pulse lengths emerging from an RLA. The beam is circulated
only a modest number of times, so the impacts of the degrading effects are then
limited, and the beam quality may be much higher than the equilibrium beam quality
inherent for rings.
Going a step further, in the Energy-Recovered Linac (ERL), the full-energy
beam is returned to the accelerating structure out of phase with respect to the
accelerating field after being used (collides, produces synchrotron radiation, drives
a specific reaction, etc.). The beam is decelerated, returning the RF power in the
beam to the accelerating structure, making this RF power available to accelerate
a subsequent beam. The resulting system retains the excellent beam quality of
a conventional linac—and, because of the recovery of significant levels of RF
power—can provide high average beam current at excellent electrical efficiency
and lower associated cost. The ERL concept is quite attractive because it provides
linac-quality/brightness beam at storage ring beam powers. With the advent of
operational ERLs, it may be possible to push average currents to levels approaching
the best lepton storage rings in existence as of 2019. Furthermore, the production of
high beam power with reduced RF drive represents improved electrical efficiency,
introducing ‘green technology’ with significant cost reductions. Energy recovery