SPS DAY
How will
Auto Qtrim work
on injection plateau
01/19/2016
Stéphane Cettour Cavé
Verena Kain
Hannes Bartosik
Outline
 Goal
 Why we do this
 How it works
Why we do this
In the SPS different effects lead to a tune shift with intensity. One part is explained by indirect space
charge as given in the next formula.
According to the formula the beam tune will shift with intensity. λ is the line charge density. The
effect goes down with 1/β2ϒ during the energy ramp, where β and ϒ are the relativistic parameters.
The difference in tune for different intensities at the flat bottom becomes significant for high
intensity LHC beams.
For optimum performance with 4 batches of 72 bunches per batch in the SPS, the tunes have to be
adjusted for each injection.
Next slide shows an example of the vertical and horizontal tune trims for the HiRadMat beam cycle
during the injection flat bottom.
Goal
The tune function (Qh and Qv; QF, QD) will be dynamically trimmed on the injection plateau as a
function of the number of injections requested.
This new functionality will be applied on these types of beam:
LHC
Hiradmat
In fact at each injection the FGC will create a tune step as shown below.
Tune H
1 injection
2 injection
Tune V
3 injection
4 injection
How it works
5 new parameters will be created on the cycle setting:
ΔQhshift(ΔIQf; ΔIQd) → add to each injection (generated at 0 by default)
ΔQvshift(ΔIQf; ΔIQd) → add to each injection (generated at 0 by default)
Delay → when we start the trim (delay from SIX.W20-CT)
Time → Rising time for the ΔI
QF
ΔI
SIX.W20-CT
Amps
QD
Delay
ΔI
Rising time
How it work
Before the cycle starts, the FGCs reads in the telegram the number of batches requested by the
injection sequencer.
The FGCs adds respectively, for each requested injection the values ΔIQF and ΔIQD to the current of
QF, QD, utilising the parameters Delay and Rising Time.
A makerule in LSA will calculate values ΔIQD and ΔIQF according to the ΔQshift parameters (H and V).
The rest of the cycle will be played with the offset generated by the step number.
Thanks for your attention