10 The Largest Accelerators and Colliders of Their Time
619
3.2 A and for electrons at 2.1 A. PEP-II was the first collider to allow top-up
injection (only a few Hz were needed) to keep the beam currents and luminosity
constant, all with full continuous data collection by the particle physics detector.
10.3.3.22 KEKB
KEKB at KEK was an asymmetric two ring collider made to measure CP violation
in the BB system and to confirm the CKM matrix [113]. Injection was made at full
energy with the KEK J-shaped linac with either e − or e + injected at 50 Hz with a
several minute switch time between modes. KEKB had a lattice with a 5π/2 phase
advance to reduce the emittance well below that of a FODO cell. It had a crossing
angle IP, used ARES RF copper cavities with an attached energy storage cell, and
superconducting RF cavities to suppress longitudinal modes. Transverse bunch-bybunch feedbacks were used to suppress instabilities. KEKB was the first collider to
use superconducting crab cavities to reduce the effects of crossing angle collisions.
KEKB also had top-up injection of both beams. KEKB holds the world’s record for
highest luminosity at 2.1 × 10 34 cm −2 s −1 .
10.3.3.23 BEPC-II
BEPC-II at IHEP was built to provide tau and charm particle physics as a factory
and also have synchrotron radiation production [114, 115]. BEPC-II is a double
ring collider with one collision point reaching up to 2.1 GeV per beam with 93
bunches. The RF system has two superconducting single cavities at 500 MHz. The
luminosity was recently limited by longitudinal instability from HOMs but was
cured by a bunch-by-bunch longitudinal feedback system. BEPC-II has delivered
several billion J/Psi events to the BES-III detector.
10.3.3.24 VEPP-2000
VEPP-2000 at BINP is a recent e+e− collider and has a single ring with two
detectors and twofold symmetry [116, 117]. The particle physics being done at
VEPP-2000 is tau and psi measurements and two gamma-physics. Injection comes
from a 900 MeV booster synchrotron with one beam at a time. A round beam
concept was applied in the ring design where a particle’s angular momentum
(M = xz’−zx’ = constant) is conserved yielding an enhancement of the beam’s
dynamic stability even with nonlinear effects of the beam-beam force included.
This scheme requires equal emittances, equal small fractional tunes, equal betas
at the IP, and no betatron coupling in the collider arcs. In practice with collisions
for the detectors, only small adjustments in the tunes are needed to arrive at good
luminosity conditions at the beginning of a fill. Observations show that a beam-beam
619
3.2 A and for electrons at 2.1 A. PEP-II was the first collider to allow top-up
injection (only a few Hz were needed) to keep the beam currents and luminosity
constant, all with full continuous data collection by the particle physics detector.
10.3.3.22 KEKB
KEKB at KEK was an asymmetric two ring collider made to measure CP violation
in the BB system and to confirm the CKM matrix [113]. Injection was made at full
energy with the KEK J-shaped linac with either e − or e + injected at 50 Hz with a
several minute switch time between modes. KEKB had a lattice with a 5π/2 phase
advance to reduce the emittance well below that of a FODO cell. It had a crossing
angle IP, used ARES RF copper cavities with an attached energy storage cell, and
superconducting RF cavities to suppress longitudinal modes. Transverse bunch-bybunch feedbacks were used to suppress instabilities. KEKB was the first collider to
use superconducting crab cavities to reduce the effects of crossing angle collisions.
KEKB also had top-up injection of both beams. KEKB holds the world’s record for
highest luminosity at 2.1 × 10 34 cm −2 s −1 .
10.3.3.23 BEPC-II
BEPC-II at IHEP was built to provide tau and charm particle physics as a factory
and also have synchrotron radiation production [114, 115]. BEPC-II is a double
ring collider with one collision point reaching up to 2.1 GeV per beam with 93
bunches. The RF system has two superconducting single cavities at 500 MHz. The
luminosity was recently limited by longitudinal instability from HOMs but was
cured by a bunch-by-bunch longitudinal feedback system. BEPC-II has delivered
several billion J/Psi events to the BES-III detector.
10.3.3.24 VEPP-2000
VEPP-2000 at BINP is a recent e+e− collider and has a single ring with two
detectors and twofold symmetry [116, 117]. The particle physics being done at
VEPP-2000 is tau and psi measurements and two gamma-physics. Injection comes
from a 900 MeV booster synchrotron with one beam at a time. A round beam
concept was applied in the ring design where a particle’s angular momentum
(M = xz’−zx’ = constant) is conserved yielding an enhancement of the beam’s
dynamic stability even with nonlinear effects of the beam-beam force included.
This scheme requires equal emittances, equal small fractional tunes, equal betas
at the IP, and no betatron coupling in the collider arcs. In practice with collisions
for the detectors, only small adjustments in the tunes are needed to arrive at good
luminosity conditions at the beginning of a fill. Observations show that a beam-beam