10 The Largest Accelerators and Colliders of Their Time
587
Table 10.2 Pre- and post-LIU main LHC beam parameters at 26 GeV/c PS extraction
Beam type
N [×10 11 p]
ε [mm mrad]
N b /extr
2018
Standard
1.4
2.3
72
BCMS
1.3
1.2
48
Post-LIU
Standard
2.6
1.85
72
BCMS
2.6
1.45
48
brighter. As foreseen in the LHC design report [8] the PS produces single bunch
beams varying in intensity from 0.05 × 10 11 to 1.2 × 10 11 protons. For the initial
multi-bunch beams 12–72 bunches per extraction at 26 GeV/c with respective bunch
spacings of 25, 50, 75 and 150 ns were routinely produced. The highest LHC bunch
intensity of 1.7 × 10 11 protons per bunch in a transverse emittance of 1.6 mm mrad
and a bunch train length of 36 bunches was reached with the 50 ns bunch spacing
that was initially used to limit electron cloud effects in the LHC. By mid-July 2015
the LHC requested the 25 ns bunch spacing with 1.15 × 10 11 protons per bunch in
a transverse emittance of 2.5 mm mrad and 72 bunches per extraction. Thanks to
the versatile PS RF system an even brighter LHC beam, based on Bunch Merging,
Compression and Splitting (BCMS), was established. Up to 1.3 × 10 11 protons per
bunch in a transverse emittance of 1.1 mm mrad and 48 bunches per extraction
are delivered to the SPS since mid-2016. The LIU project aims at increasing the
bunch intensity to 2.6 × 10 11 protons per bunch for both beam types as given in
Table 10.2.
For fixed-target experiments at the Super Proton Synchrotron (SPS), a 14 GeV/c
proton beam (3 × 10 13 per pulse) was spilled out over five turns by cutting it with
an electro-static septum in horizontal phase space in order to fill by box-car stacking
5/11 parts of the SPS circumference being 11 times longer than the one of the CPS.
A second CPS beam pulse fills further 5/11 parts, thus leaving 1/11 for the kicker
rise-times. Since 2010 a novel scheme, using a fourth order betatron resonance for
capturing the beam in five stable islands in the horizontal phase space, avoids the
losses at the electrostatic extraction septum [9].
The slow-extraction based on a third-order betatron resonance is still in use to
produce primary 24 GeV/c proton beams. Up to 5 × 10 11 protons can be spilled out
in up to 450 ms for the production of secondary beams for fixed-target experiments
at the CPS, but also for primary protons to the IRRAD and CHARM irradiation
facilities [10].
As soon as L2 was available, L1 was modified to provide Deuterium and αparticle beams for collisions in the ISR and, later, Sulphur beams for fixed target
experiments in the SPS. In 1994, L1 was replaced by linac 3 (L3) providing
4.2 MeV/amu Pb +53 ions which, fully stripped after CPS extraction, are used for
fixed-target experiments in the SPS. Since 2010 the lead ions are also fast-ejected to
the SPS for lead-lead collisions in LHC. They no longer pass through the PSB but a
small storage ring, the Low Energy Ion Ring (LEIR), acts as accumulator between
the fast-cycling L3 and the slow-cycling CPS and is equipped with stochastic and
587
Table 10.2 Pre- and post-LIU main LHC beam parameters at 26 GeV/c PS extraction
Beam type
N [×10 11 p]
ε [mm mrad]
N b /extr
2018
Standard
1.4
2.3
72
BCMS
1.3
1.2
48
Post-LIU
Standard
2.6
1.85
72
BCMS
2.6
1.45
48
brighter. As foreseen in the LHC design report [8] the PS produces single bunch
beams varying in intensity from 0.05 × 10 11 to 1.2 × 10 11 protons. For the initial
multi-bunch beams 12–72 bunches per extraction at 26 GeV/c with respective bunch
spacings of 25, 50, 75 and 150 ns were routinely produced. The highest LHC bunch
intensity of 1.7 × 10 11 protons per bunch in a transverse emittance of 1.6 mm mrad
and a bunch train length of 36 bunches was reached with the 50 ns bunch spacing
that was initially used to limit electron cloud effects in the LHC. By mid-July 2015
the LHC requested the 25 ns bunch spacing with 1.15 × 10 11 protons per bunch in
a transverse emittance of 2.5 mm mrad and 72 bunches per extraction. Thanks to
the versatile PS RF system an even brighter LHC beam, based on Bunch Merging,
Compression and Splitting (BCMS), was established. Up to 1.3 × 10 11 protons per
bunch in a transverse emittance of 1.1 mm mrad and 48 bunches per extraction
are delivered to the SPS since mid-2016. The LIU project aims at increasing the
bunch intensity to 2.6 × 10 11 protons per bunch for both beam types as given in
Table 10.2.
For fixed-target experiments at the Super Proton Synchrotron (SPS), a 14 GeV/c
proton beam (3 × 10 13 per pulse) was spilled out over five turns by cutting it with
an electro-static septum in horizontal phase space in order to fill by box-car stacking
5/11 parts of the SPS circumference being 11 times longer than the one of the CPS.
A second CPS beam pulse fills further 5/11 parts, thus leaving 1/11 for the kicker
rise-times. Since 2010 a novel scheme, using a fourth order betatron resonance for
capturing the beam in five stable islands in the horizontal phase space, avoids the
losses at the electrostatic extraction septum [9].
The slow-extraction based on a third-order betatron resonance is still in use to
produce primary 24 GeV/c proton beams. Up to 5 × 10 11 protons can be spilled out
in up to 450 ms for the production of secondary beams for fixed-target experiments
at the CPS, but also for primary protons to the IRRAD and CHARM irradiation
facilities [10].
As soon as L2 was available, L1 was modified to provide Deuterium and αparticle beams for collisions in the ISR and, later, Sulphur beams for fixed target
experiments in the SPS. In 1994, L1 was replaced by linac 3 (L3) providing
4.2 MeV/amu Pb +53 ions which, fully stripped after CPS extraction, are used for
fixed-target experiments in the SPS. Since 2010 the lead ions are also fast-ejected to
the SPS for lead-lead collisions in LHC. They no longer pass through the PSB but a
small storage ring, the Low Energy Ion Ring (LEIR), acts as accumulator between
the fast-cycling L3 and the slow-cycling CPS and is equipped with stochastic and