CERN
LHC Project Document No.
CH-1211 Geneva 23
Switzerland
LHC-MD-0020 rev 0.1
CERN Div./Group or Supplier/Contractor Document No.
BE-OP
the
EDMS Document No.
Large
Hadron
Collider
1210692
project
Date: 2012-04-04
LHC MD Test Program – MD Class xx
DYNAMIC APERTURE AND NON-LINEAR
MEASUREMENTS WITH THE MKA
Abstract
The kick strength of the MKA at 450GeV is being upgraded to allow for kicks up to15
beam sigma. Until 2012, the MKA had been limited to 6  kicks, which is insufficient for
dynamic aperture studies. The upgraded MKA will allow sampling the regime between
11 and 13 , which is the theoretical expectation based on detailed tracking
simulations. A benchmarking of these simulations with a direct measurement at the LHC
will largely benefit the ongoing HL-LHC upgrade studies.
This note describes the procedures to be followed during the MD.
Prepared by:
Checked by:
Approved by:
Frank Schmidt for the
LHC non-linear
measurement team
rMPP members
J.Wenninger
R.Schmidt
M.Zerlauth
Distribution list:
LHC Engineers in charge, LHC operators
Etienne Carlier, Viliam Senaj, Roger Andrew Barlow.
LHC Project Document No.
LHC-MD-0020 rev 0.1
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History of Changes
Rev. No.
Date
Pages
Description of Changes
0.1
27-Jan-2012
All
First draft presented to rMPP.
0.2
04-April-2012
All
Completed version – sent for approval
LHC Project Document No.
LHC-MD-0020 rev 0.1
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Table of Contents
1.
INTRODUCTION ........................................................................................4
2.
BEAM REQUIREMENTS ..............................................................................4
3.
MKA UPGRADE ..........................................................................................4
5.
ASPECTS RELEVANT FOR MACHINE PROTECTION .....................................5
6.
INABLE AND DISABLE THE MKA ................................................................5
7.
CONCLUSIONS ..........................................................................................6
LHC Project Document No.
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1. INTRODUCTION
This note summarises the part of the programme of dynamic aperture and non-linear
measurements at 450 GeV at the LHC that is relevant for the use of MKA with upgraded
strength. These measurements are done by kicking one pilot bunch of 1010 protons with
a single kick of the MKA up to amplitudes in excess of 12  (assuming a transverse
emittance of 3.75 m). For each measurement a fresh pilot has to be injected and the
MKA strength will be slowly increased until losses become significant. At low amplitude,
where no losses can be observed, many kicks will be applied systematically to study
amplitude dependent parameters like anharmonicities and resonance driving terms. At
large amplitude the main emphasis is to measure the dynamic aperture with good
precision. The outcome of these experiments will allow to benchmark our tracking
simulations in view of the HL-LHC upgrade study.
2. BEAM REQUIREMENTS
The beam requirements for the proposed dynamic aperture MD are listed in Tab. 1.
The standard information provided in the MD request is listed, with additional details
on aspects relevant for machine protection.
Table 1: Beam parameters and machine configuration for the measurements.
Beams required
Both beams
Beam energy [GeV]
450
Optics
nominal
Bunch intensity
1x1010p
Number of bunches
1 per beam / 2 per beam
Transv. emittance [m rad]
3.5 m
Bunch length [ns @ 4s]
Not relevant
Optics change
None
Orbit change
None
Collimator changes
YES: all out except primaries at 12 
RF system change
No.
Feedback changes
None
Configuration of MP
Safe beam flag.
3. MKA UPGRADE
The MKA system has been upgraded towards the 2011/2012 Christmas Technical Stop. The
power converters of 1 kV used so far have been replaced by the original power converters of 4
kV, but they will be hardware limited at 1.8 kV. Modifications to the triggering and electrical
circuits were also made to obtain a correct pulse shape. As an example, the pulse shape for
one MKA pulsed at 1.9 kV is given in fig. 1. The estimated maximum excursion with a voltage
of 1.8 kV is between 14.2 and 15.1 sigma, assuming a normalised emittance of 3.75 m.
LHC Project Document No.
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Figure 1: Example of MKA pulse shape, MKA-Vertical B1, pulsed at 1.9 kV. The time
scale is 10 s per division.
4. PROCEDURES TO BE FOLLOWED DURING THE MD
The following procedures are proposed during the MD for B2
Description
Check
1. Access to enable MKA. Make local test pulse to check
functionality. MKA maximum voltage limited to 1.8 KV on the
2 MKAs of B2.
VS / JU
2. Check safe beam flag threshold at 5e10 protons.
Turn the keys to MKA position for the 2 MKAs of B2.
EIC / JU
3. Retract all collimators, except TCPs at 12 sigma
Check beam permit / collimator interlocking.
EIC / JU
4. Pulse the 2 MKAs of B2 and check the waveforms and timing
on OASIS.
JU
5. Inject 2 bunches 1e10 p+, emittance of 3.5 um at bunch
positions 1 and 1400 (to be checked) for B2.
EIC
6. Kick with horizontal MKA B2 with a single kick of up to 10
sigma in steps of 1 sigma before significant beam losses are
noticed. With 2 bunches per circumference one can apply 2
kicks per injection.
FS
7. Kick with vertical MKA B2 with a single kick of up to 10 sigma
in steps of 1 sigma and stop before significant beam losses
are noticed. With 2 bunches per circumference one can apply
2 kicks per injection.
8. Repeat steps 6 -7 from 10 to 12 sigma in smaller kick
increments of 0.5 sigma. Again avoid large losses.
Collimators remain at 12 sigma.
9. Repeat step 8 for kicks larger than 12 sigma but in very small
kick increments of 0.2 sigma. The collimator should be
retracted in 0.5 sigma steps accordingly. Ultimate care has to
be taken to avoid any significant losses!
FS
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10.Put keys back to MKQ and remove keys.
JU
11.Access to disable MKA.
JU
5. ENABLE AND DISABLE THE MKA
Enabling the upgraded strength of the MKA before the non-linear MD and disabling it
after the completion of the measurements and prior to switching to the next MD is a
must. This will require an access, which has certain implications in terms of time, and
such a time should be counted on the allocated beam time for this MD. Furthermore,
the safety conditions required to grant the access impose to have the magnets at a
current lower than the injection level. When coming from a previous MD at top energy,
the magnets are already brought at such a lower-than-injection level. Hence, the only
overhead is the access time. However, after the MD the magnets will need to be
brought down to such a special current value, this meaning that they will be on the
wrong side of the hysteresis branch afterwards. This prevents starting a new MD
without having cycled the magnets. Such an overhead adds to the standard access
time. Under these conditions, the stringent safety rules imposed by MP for using the
upgraded strength of the MKA impose a boundary condition to the MD schedule, as for
efficiency, the non-linear MD should be the last one of the block, such that the final
cycling can be suppressed and only the access time should be taken from the MD
allocated time.
6. CONCLUSIONS
The MKA has been successfully upgraded to allow for single kicks up to 15 . This will
allow measuring the LHC dynamic aperture at 450 GeV with good precision. The much
stricter requirements to switch the MKA on and off for each such experiment makes it
completely safe for nominal operation. With a beam of two bunches of 11010 protons no
quench nor danger to the machine can be expected, in particular since we will increase
the kick strength in small steps before large losses will be observed. Moving out the
collimators to 15-16  should therefore not endanger the machine in any way.
A clear procedure for the MD has been established which should guarantee the safety of
the machine and result in an efficient use of the MD time.