616
K. Hübner et al.
10.3.3.12 PETRA
PETRA at DESY had four interaction points and operated up to an energy of 24 GeV
per beam with 2 × 2 bunches [101]. Additional seven cell RF cavities were installed
over the years to achieve these energies. Second harmonic cavities (1 GHz) were
installed to reduce the bunch length, cure a vertical single bunch instability and
reduce several synchrotron-betatron resonances. The free space for the detector was
reduced to ±4.45 m using mini-beta insertions allowing a vertical beta of 6 cm. The
injected positrons were predamped in the accumulator storage ring PIA. PETRA
is known for the discovery of the Gluon and for QCD studies. PETRA has been
upgraded to a low emittance light source.
10.3.3.13 CESR
CESR at Cornell operated for B-meson studies for 20 years [102, 103]. The
particle physics results included V ub observations of “penguin” modes, b → sγ
decays, CKM matrix constraining the unitarity triangle, and B mass and lifetime
measurements. Injection was from a 200 MeV linac and a 12 GeV synchrotron. With
electrostatic plates installed, CESR could collide up to 27 bunches separated in the
accelerator arcs by what is now called a “Pretzel orbit” that was used to suppress
parasitic beam-beam collisions and the related tune shifts. Several other colliders
went on to use this technique to increase the number of bunches. It was discovered
at CESR that a horizontal tune just above the half integer (<0.51) increased
significantly the beam-beam limit allowing higher luminosity. Superconducting
single-cell cavities with HOM damping were installed in CESR allowing up to
325 mA beams each of electrons and positron to the stored. The CESR interaction
region used a combination of permanent-magnet and superconducting technologies
for the vertically focusing quadrupoles. A ±2.5 mrad uncompensated IP crossing
angle was ultimately used. Superconducting wigglers were later installed to allow
operation at lower energy at the charm threshold. CESR is presently being used as
a light source and as a test accelerator to study low emittance damping rings and
electron cloud physics.
10.3.3.14 VEPP-4
VEPP-4 at BINP has been colliding beams for a long time including two modernizations [104]. Over the years, the vertical beta at the IP was reduced to
5 cm, superconducting wigglers were added to increase the luminosity, and a
superconducting RF cavity was installed for bunch length reduction allowing the use
of the lower IP beta. Bunch currents were limited by beam induced wakefields in the
vacuum chambers at the level of 17 mA. Eight pairs of electrostatic separation plates
allow two bunch operation in a Pretzel scheme. A transversely polarized beam could
be injected into VEPP-4 from VEPP-3 for accurate measurements of the masses of
K. Hübner et al.
10.3.3.12 PETRA
PETRA at DESY had four interaction points and operated up to an energy of 24 GeV
per beam with 2 × 2 bunches [101]. Additional seven cell RF cavities were installed
over the years to achieve these energies. Second harmonic cavities (1 GHz) were
installed to reduce the bunch length, cure a vertical single bunch instability and
reduce several synchrotron-betatron resonances. The free space for the detector was
reduced to ±4.45 m using mini-beta insertions allowing a vertical beta of 6 cm. The
injected positrons were predamped in the accumulator storage ring PIA. PETRA
is known for the discovery of the Gluon and for QCD studies. PETRA has been
upgraded to a low emittance light source.
10.3.3.13 CESR
CESR at Cornell operated for B-meson studies for 20 years [102, 103]. The
particle physics results included V ub observations of “penguin” modes, b → sγ
decays, CKM matrix constraining the unitarity triangle, and B mass and lifetime
measurements. Injection was from a 200 MeV linac and a 12 GeV synchrotron. With
electrostatic plates installed, CESR could collide up to 27 bunches separated in the
accelerator arcs by what is now called a “Pretzel orbit” that was used to suppress
parasitic beam-beam collisions and the related tune shifts. Several other colliders
went on to use this technique to increase the number of bunches. It was discovered
at CESR that a horizontal tune just above the half integer (<0.51) increased
significantly the beam-beam limit allowing higher luminosity. Superconducting
single-cell cavities with HOM damping were installed in CESR allowing up to
325 mA beams each of electrons and positron to the stored. The CESR interaction
region used a combination of permanent-magnet and superconducting technologies
for the vertically focusing quadrupoles. A ±2.5 mrad uncompensated IP crossing
angle was ultimately used. Superconducting wigglers were later installed to allow
operation at lower energy at the charm threshold. CESR is presently being used as
a light source and as a test accelerator to study low emittance damping rings and
electron cloud physics.
10.3.3.14 VEPP-4
VEPP-4 at BINP has been colliding beams for a long time including two modernizations [104]. Over the years, the vertical beta at the IP was reduced to
5 cm, superconducting wigglers were added to increase the luminosity, and a
superconducting RF cavity was installed for bunch length reduction allowing the use
of the lower IP beta. Bunch currents were limited by beam induced wakefields in the
vacuum chambers at the level of 17 mA. Eight pairs of electrostatic separation plates
allow two bunch operation in a Pretzel scheme. A transversely polarized beam could
be injected into VEPP-4 from VEPP-3 for accurate measurements of the masses of