6 Design and Principles of Synchrotrons and Circular Colliders
275
used as “phased arrays” [119, 120]. As for travelling wave structures starting from
the TEM type slotted line version of Faltin [121] McGinnis developed a related
device [122] not based on a TEM line, but essentially a waveguide directional
coupler with slots masks for the coupling. Those waveguide type slot array couplers
have the advantage (in contrast to the Faltin version) that they can operate efficiently
also for highly relativistic beams and they exhibit a very high longitudinal and
transverse sensitivity over a bandwidth of several 100 MHz in the GHz region. As
a particular development the kicker structure for the BNL RHIC bunched beam
stochastic cooling system [123–125] is worth mentioning. It consists of an array
of cavities which are cut in length and can be opened by a mechanical plunging
mechanism in order to let the injected beam pass without aperture limitations.
Another travelling wave structure is the perforated structure which was originally
proposed in 2011 [126] and later developed for HIRFL-CSRe stochastic cooling. A
large number of small slots in the electrode provides distributed inductive loading,
slowing down the phase velocity of the travelling wave structure for the low beta
beams. This device is very broadband and operates from low frequencies onwards
as a forward coupler. Even for 2.76 m long electrodes used in HIFRL-CSRe, it can
be used from a few MHz to 1.2 GHz [127].
Another very promising recent development for pick-ups and kickers are “slot
ring” structures [128]. These structures were originally developed for the High
Energy Storage Ring (HESR) of the FAIR project at GSI, Germany and successfully
tested at the Nuclotron (JINR, Russia) for longitudinal cooling and at COSY (FZJ)
for longitudinal and transverse cooling. Slot ring couplers have a fixed aperture and
can be used for all three cooling planes simultaneously [128].
In CERN’s anti-proton decelerator AD stochastic cooling is employed at
3.57 GeV/c and 2 GeV/c in both transverse planes and for the longitudinal plane
(filter cooling) [129]. The current system uses a set of two kickers and pick-ups,
each combining one transverse plane and the longitudinal cooling, with a total of
4.8 kW installed power. It is undergoing a consolidation and upgrade [130] which
is including a notch filter with optical delay lines. Cooling times of 15–20 s reduce
transverse emittances to 3–4 π mm rad and Dp/p to ±0.3 × 10 −3 at 3.57 GeV/c
and to ±0.08 × 10 −3 at 2 GeV/c at intensities of 5 × 10 7 antiprotons. The system
uses a bandwidth of one octave between 850 MHz and 1.7 GHz. This is the actual
status in early 2019.
In parallel, CLASS A solid state amplifiers [131] (kicker driver) gradually took
over from TWT (travelling wave tube) units, although TWTs are still in operation for
stochastic cooling e.g. at Fermilab where they work reliably. Notch filters, required
for Thorndahl type longitudinal cooling (filter cooling) are implemented since about
1990 with good success in optical fibre technology [125, 132].
Optical signal transmission across the ring (Fermilab de-buncher) has been
realized with a laser beam in an evacuated metal pipe (no signal fluctuation from
temperature effects of air and humidity on the laser beam). The driving force to
select this method of signal transmission was the very tight requirement in terms of
transmission delay and delay stability. Anything slower than speed of light would
not have permitted timely arrival of the correction signal at the kicker. In 2017 very
275
used as “phased arrays” [119, 120]. As for travelling wave structures starting from
the TEM type slotted line version of Faltin [121] McGinnis developed a related
device [122] not based on a TEM line, but essentially a waveguide directional
coupler with slots masks for the coupling. Those waveguide type slot array couplers
have the advantage (in contrast to the Faltin version) that they can operate efficiently
also for highly relativistic beams and they exhibit a very high longitudinal and
transverse sensitivity over a bandwidth of several 100 MHz in the GHz region. As
a particular development the kicker structure for the BNL RHIC bunched beam
stochastic cooling system [123–125] is worth mentioning. It consists of an array
of cavities which are cut in length and can be opened by a mechanical plunging
mechanism in order to let the injected beam pass without aperture limitations.
Another travelling wave structure is the perforated structure which was originally
proposed in 2011 [126] and later developed for HIRFL-CSRe stochastic cooling. A
large number of small slots in the electrode provides distributed inductive loading,
slowing down the phase velocity of the travelling wave structure for the low beta
beams. This device is very broadband and operates from low frequencies onwards
as a forward coupler. Even for 2.76 m long electrodes used in HIFRL-CSRe, it can
be used from a few MHz to 1.2 GHz [127].
Another very promising recent development for pick-ups and kickers are “slot
ring” structures [128]. These structures were originally developed for the High
Energy Storage Ring (HESR) of the FAIR project at GSI, Germany and successfully
tested at the Nuclotron (JINR, Russia) for longitudinal cooling and at COSY (FZJ)
for longitudinal and transverse cooling. Slot ring couplers have a fixed aperture and
can be used for all three cooling planes simultaneously [128].
In CERN’s anti-proton decelerator AD stochastic cooling is employed at
3.57 GeV/c and 2 GeV/c in both transverse planes and for the longitudinal plane
(filter cooling) [129]. The current system uses a set of two kickers and pick-ups,
each combining one transverse plane and the longitudinal cooling, with a total of
4.8 kW installed power. It is undergoing a consolidation and upgrade [130] which
is including a notch filter with optical delay lines. Cooling times of 15–20 s reduce
transverse emittances to 3–4 π mm rad and Dp/p to ±0.3 × 10 −3 at 3.57 GeV/c
and to ±0.08 × 10 −3 at 2 GeV/c at intensities of 5 × 10 7 antiprotons. The system
uses a bandwidth of one octave between 850 MHz and 1.7 GHz. This is the actual
status in early 2019.
In parallel, CLASS A solid state amplifiers [131] (kicker driver) gradually took
over from TWT (travelling wave tube) units, although TWTs are still in operation for
stochastic cooling e.g. at Fermilab where they work reliably. Notch filters, required
for Thorndahl type longitudinal cooling (filter cooling) are implemented since about
1990 with good success in optical fibre technology [125, 132].
Optical signal transmission across the ring (Fermilab de-buncher) has been
realized with a laser beam in an evacuated metal pipe (no signal fluctuation from
temperature effects of air and humidity on the laser beam). The driving force to
select this method of signal transmission was the very tight requirement in terms of
transmission delay and delay stability. Anything slower than speed of light would
not have permitted timely arrival of the correction signal at the kicker. In 2017 very