SPS Cycles for LHC
Injection
The LHC baseline filling scheme has been changed
for Protons.
The following is the new scheme based on
the so-called 72 bunch scheme in the PS.
These are schematic views of the SPS cycles for LHC filling and don't
pretend to be completely accurate.
Both cycles are conceived
'dedicated', in that during the time they are run, the SPS will only serve the
LHC.
Protons The proton cycle in
the SPS will consist of either 3 or 4 PS injections at 3.6s intervals.
Each PS batch will contain 72 bunches, spaced by 25ns. The momentum at
injection will be 26 GeV/c. For the nominal LHC beam the intensity per
bunch will be ~1.1x10+11. The injection plateau in the SPS will
therefore last (up to) 10.8s.
The acceleration phase is about 8.3 s
and brings the beam up to 450 GeV/c. The speed is determined primarily by the RF
power requirements.
A 1 s flat-top is presently assumed. This will be
used to prepare the extraction equipment (bumpers etc.) and perform any RF
re-phasing necessary to put the beam in the correct location in the LHC.
Fast extraction is used (all beam extracted within the same SPS
turn). It will either send the beam to TI 2 (via the West Extraction channel),
or to TI 8 (via the new East Extraction channel).
For a 3-batch cycle the total intensity in the SPS will be
2.38x10+13 protons with 26% of the SPS circumference containing beam.
For a 4-batch cycle the total intensity in the SPS will rise to
3.17x10+13 protons and will occupy around 35% of the SPS
circumference.
The above cycle is repeated 12 times for each LHC
ring. 3-batch and 4-batch cycles will be interleaved in the form...
334 334 334 333
... in order to
fill each ring with a total of 2808 bunches.
Hence the LHC filling time
will be 4.3 minutes per ring.
The bunch pattern for the LHC, SPS and PS therefore looks like this
...
Neglecting the beam
dump kicker hole, the above pattern has 4-fold symmetry. This is important
for questions of beam-beam. In this scheme, with the exception of the beam
dump hole, each of the 4 LHC experiments will see full holes in the collision
schedule. There are no crossings where a bunch passes through an
experiment during a hole in the other beam. This, however, will occur
during the beam dump hole.
Heavy Ions
(Pb82+)
In each cycle of the
PS, 4 bunches of fully stripped Pb82+ ions will be produced.
Each bunch will contain 1.6x10+8 ions. The injection energy will be
5.11 GeV/c/u. Thirteen (13) such injections spaced by 3.6 s will be made
into the SPS, giving a total of 52 bunches.
At injection the bunch spacing
is 125.31 ns. As the beam is accelerated to 177 GeV/c/u, the bunch spacing
will shrink to 124.75 ns.
Once again a 1 s flat top is foreseen and fast
extraction will be used to send the beam to either TI 2, or TI 8.
The
bunch pattern for Pb82+ is a little more complex! It looks like this
...
Description
The PS will transfer 4 bunches of ions during each 3.6 s
cycle into the SPS. These will be stacked in the SPS to form a continuous
train of bunches, 52 bunches long. This batch is accelerated and passed
into the LHC.
In the LHC 3 of these batches are injected with a gap of 7
bunches between each one (to allow for the LHC injection kicker rise time). This
ensemble forms an LHC bunch train.
There will be 4 of these bunch trains in
the LHC with 8 bunches missing between each one PLUS 25 ns. The last bunch
train is shortened to allow for the LHC beam dump kicker rise time.
In this case the final batch delivered to the LHC will consist of only 9
injections from the PS, instead of the usual 13. In total 608 bunches per
ring will be injected. The filling time of the LHC with this scheme will be 9.5
minutes per ring.
The bunch harmonic number with 125 ns spacing is not an integer at
712.8. However the arrangement of the bunches in the above scheme is once
again designed to generate 4-fold symmetry (neglecting again the beam dump
hole). This is acieved by arranging the bunches into 4 trains. The spacing
between the trains is not an integer number of bunches. It corresponds to 8.2
bunches.
For comments and changes send e-mail to mailto:Paul.Collier@cern.ch
Copyright
CERN
modified 11/09/2000
