iBump Feedback Tuning

Yoshimi. SatohMitsubishi Electric System & Service Co. Ltd.,1. Introduction➳
This system makes a bump in the HER orbit just near
the colliding point.➳

2. iBump Target Tuning➼In the begging of the KEKB commissioning, wetuned the iBump by setting a target.
➼At the time, we used this monitor to set the target
searching for the high specific luminosity point.
➼We found a problem with this tuning. The targetof the horizontal beam-beam kick changes withbeam current.

Figure 1: iBump monitor.

3. Programmable H-Target Changer➳➳➳➳➳➳➳➳➳➼We can set the horizontal target value as afunction of the LER beam current.
➼The pattern of horizontal target had to bechanged for almost every fill.

Figure 2: Programmable H-TargetChanger

4. Effects of the H-offset tuning on luminosityand beam size
➼The change of H-offs et induc ed a change i nluminosity, and a simultaneous LER beam size
HazureEgurechange.
ĂIncrease the H-offsetýLERýbeamýsizeýdecr eases alon g w i t h theluminosity.
LER ʠýýýýýýýŤHAZURE.
ĂDecrease the H-offsetýLER beam size, andluminosity will increase.
LspecĂDecrease the H-offset furtherýLER beam size will continue
increasing, but theýFigure 3: feedback monitor.[3]luminosity will quickly
decrease .
ǌ

5-1. H-Offset Direct Tuning
First, we checked the luminosity and the beamsize.
Offset minus➼Luminosity : low
LER beam size : small➳➳➳➳➳➳ğ HAZURE➼ Shift the H-offset value in theLER ʠEgure
minus direction .
Hazureğ LER beam size will increase
and th e l umin osi ty wil l als oincrease.
Lspec➼ Continue this procedure.
ğLuminosity : quickly dropFigure 4-1: iSize Feegback
LER beam size : continue
Monitor.
increase. ğEGURE stateǌ

5-2. H-Offset Direct Tuning➼Encounter the EGURE state, evenif we increase the H-offset in theHAZURE direction, we can not Egure-Hazushi
recover the luminosity and beamsize.
➼Set a large value, about ten times
Best Tuning
the usua l v alue, in the p lu sLER ʠdirection to decrease➳the➳LERbeam➳size.
ğEGURE-HAZUSHI.
➼The best tuning point of the HLspec
offset should be just before theEGURE position.
➼Since the tuning guideline wasFigure 4-2: iSize Feegback Monitor.
not clear, the tuning point varied
for different operators.
ǌ6. Guideline for H-Offset Setting
We have found that there was a correlation between thekick angle of a steering magnet ZHQC2LE at nearinteraction point and the H-offset.

➼The ratio of H-offset to theKRB is some constant theluminosity is high.
➳➼The luminosity decreases
due to EUGRE or HAZURE.

Hazure Egure

Best Tuning

Luminosity

Figure 5: Relation be tween the KRB of theZ H QC 2 L E, t h e H - of fset v a l ue a nd t h e

7. H-Offset Easy Feedback System
We introduced a tool to keep this ratio at theoptimum value .
➼This panel controls the KRB ofZH QC2L E➳ and th e H-offset
value to➳keep the optimum ratio.
➼Every operator could➳maintainst a b le➳ l um i no s ity w ith s m a ll
EGURE or HAZURE.
➼Same problem as in the case of theprogrammable➳H-target changera l th o u gh t h e v a ri a tion of theluminosity is much smaller.

Figure 6: H-offset easy feedback
panel.8. H-Offset Beam Size Feedback System
We will return to the use of beam size as a tuningparameter.
➼The H-offset is searched and seta utomatically➳ to➳ r ea li ze➳ thetarget beam size.
➼The➳target➳size➳can➳be➳automatically incorporating with thebeam size changer.
➼Now, we ar e ma in ly usi ng th isfeedback system during the fill.
Figure 7: H-offset Beam Size feedbackpanel

9. H-Offset Life Feedback System
Usually we encountered crucial LER beam life loss
during these first ten minutes.
➼If we start to decrease the H-offset
val ue to obtain high lumi nosity
without attention to this beam life loss.
This tuning will be a trigger for anundesired beam loss.
➼We have also introduced another Hoffset feedback tool to maintain beamlife.
➼The➳H-offset➳value➳is➳changing
automatically by this tool to realize
the target lifetime .
Figure 8: H-offset Life feedback panel.

10-1. Summary

Fill starting

Injection

DirectTuning Life Feedback Size Feedback
Figure9. Luminosity history10-2. Summary• In the important first five minutes of the experiment,we musttune the iBump very carefully, using luminosity, beam size andbeam life information.
•We can not use any feedback tools.At present we still have touse the direct tuning method in the first five minutes.

•Since operator experience is very important in this tuning, thismethod is not easy for everyone.

• We must establish clearly guidelines for iBump tuning.