1 PEP Status M. Sullivan MAC Review Nov. 15-17, 2007 M. Sullivan for the PEP-II Team Machine...

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PEP StatusM. Sullivan

MAC ReviewNov. 15-17, 2007

M. Sullivanfor the

PEP-II Team

Machine Advisory Committee ReviewNovember 15-17, 2007

Run 6 Summary and

Run 7 Startup Plans

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Outline

• Run 6 summary– Brief history– Magnet protection failure– HER instability aborts– MDs– Records

• Run 7 startup– Initial startup plan– Plan for the first 2-3 months– MDs– 3S?

• Summary

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B-Factory Overall Best Parameters

• Parameter PEP-II

• (LER/HER)

• Circumference (m) 2200

• Beam energy (GeV) 3.1/9.0

• Number of bunches 1732

• Beam currents (mA) (e+/e-) 2900/1900

• Horizontal emittance (nm) 30/50

• y* (mm) 9-11

• Bunch length (mm) 10-11

• y (+/-) 0.065/0.045

• IP beam sizes (microns) (x/y) 120/4

• Luminosity (x 1034/cm2/s) 1.2

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Improvements and Upgrades for Run 6

• Two new HER RF stations in and working. We now have filled out the RF systems for both rings. Eleven klystrons (10 SLAC type) for the HER and 4 klystrons (2 SLAC type – one SLAC tube added this downtime) for the LER.

• LER BPM button removal in IR2 and BPM replacement in 5 of 6 arcs

• New skew quad fix for IR2 LER x-y coupling found and implemented. Specific luminosity is higher. More luminosity gain is expected in the future.

• Fast dither IP feedback in and working on a routine basis

• Vertical vibration in IR support tube damped with BaBar’s help

Schwarz, Rivetta, Van Winkle

Wittmer, Yan

Fisher

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Run 6 Difficulties

• Our startup last January was slower than we had hoped

– Reconfiguring the RF systems to include the new stations took longer than planned

– Soon after startup we discovered that we had to remove a vacuum valve from a place where the previous valve had heated up. We had installed a new valve together with a HOM absorber. We hoped we had mitigated the HOM power in this location where the level is high. Apparently not enough.

– We also developed a vacuum leak in a transition piece in Region 6 that had to be replaced

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More Run 6 History• In early April we discovered a vacuum leak in close to the

detector on one of the new vacuum chambers we had installed

• We also discovered the support tube inside the detector was vibrating vertically at about 9 Hz. While devising a mechanical fix we used the fast lumi feedback to cancel the motion.

• By the middle of April we realized we would have to take out the new chamber and put the old one back in and we set that up for the first week in May

• On May 1st we turned off and started work on replacing the leaking chamber

• Unfortunately, the power to the Q2 septum magnet near this chamber did not get turned off before the water to the magnet was shut off (40 kW)

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Q2 magnet • The magnet coils heated up and damaged the insulation.

The power supply finally tripped on a ground fault.

• We had a failure of three systems/procedures at the same time that caused this magnet to overheat

• We have improved our procedures and fixed the hardware so that this can not happen again

• We did have a spare set of magnet coils for this magnet

• We lost an extra week in May removing and replacing the coils in the Q2 magnet

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Side view of BaBar Q2 magnet

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The front end of Q2

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Removing the Top of Q2

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The top half being lifted out

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The bottom of Q2

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Removing the bottom half of Q2

Many, many thanks go to all the support groups and people including the BaBar people who made it possible for us to recover from this in a safe and timely manner.

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Run 6 History (2)

• In June and July we went into the ring on three separate occasions to replace flex flange RF seals that we had identified as causing a large number of beam aborts

• In spite of these difficulties we managed to break most of our luminosity records

• From mid July to the end (Sept. 4) we ran more reliably (very little down time, although the beam abort rate was still high)

Sullivan

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Flex flange RF seal

Silver vapor from plated washer

Molten CuCu vapor

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MDs• We had several MDs

– In April we installed PM skew quads into the LER to compensate the coupling from the BaBar solenoid before reaching the arcs. This allows us to lower the LER vertical emittance.

– In mid July we tried to close the abort gap. This would make the phase transient equal and zero for both rings. We found we could not close the gap much more than the value we currently run at without making the HER unstable which we think is due to trapping too many ions.

– Coupling MD to try to lower the LER coupling

– In August we tested the HER 90 deg lattice. The test was very successful and we plan to install the 90 deg lattice into the HER in early January.

– We also had a beam-beam MD where we increase the beam bunch current with a subset of the total bunches

– We had several RF MDs to try to raise the beam currents

Wittmer

Wienands

Wittmer

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New Skew Magnets to Improve LER Vertical Emittance

10 to 50% gain at fixed currents

Physicist design (F-J. Decker)

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11.692650x1900

858

311

Run 6 nos.

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Downtime Activities

• Install the last of the new LER bpms• Replace all of the HER flex flange RF seals• IR2 straight

– Install the repaired HER Q4 chamber– Install the two new LER Q5 chambers– Replace a leaky HER frangible link– Replace 5 bellows in the HER with HOM absorbing

bellows– Replace 12 LER bellows with HOM absorbing

bellows• Replace a ceramic window in RFS 12-1A cavity• Replace the horizontal transverse kicker in the LER

Done

Done

Done

Done

>85% Done

Done

Done

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HOM absorbing bellows

Absorbing tiles

NovokhatskiWeathersbyKuritaReeckMetcalfe

In IR 2 we are replacing 5 bellows sections in the upstream LER and HER and 7 units in the downstream LER with bellows modules that contain HOM absorbing tiles. We hope to reduce the HOM power in this area

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HER upstream beam line

NEGs

NEGs

Good screens Weak screens

Weak screens

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LER upstream beam line

AbsorberNEG

NEG

Fixed collimator

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LER downstream beam line

SR mask

First bpms that dropped in this area

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Beam aborts• In February we lost the beam 229 times (about 8.8

losses each running day)

• In August we lost the beam 263 times (about 8.8 losses each day)

• Each beam abort is about 30 min of lost integrated lumi

• RF aborts are a significant fraction of the total abort rate (about 2.4 losses a day)

• The largest single category of aborts is from an unstable HER beam usually related to a vacuum spike. We believe most of these are from failing RF seals.

Bertsche, Van Winkle

DeBarger, Sullivan

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Luminosity Peak

• The avenues we see for improving the peak luminosity are:– Shorten the beam bunches

– Lower beta Y*

– Increase the beam currents

– Improve the vertical beam emittance

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Luminosity Integration

• The avenues we see for improving the integrated luminosity are:– Reduce the number of beam aborts

– Reduce the number of beam aborts

– Reduce the number of beam aborts

– Increasing the peak lumi helps as well as long as the abort rate does not increase too much

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Startup Plans

• Start up with the saved machine from Sept. (60 deg lattice for the HER)

• Raise the LER RF voltage from 4.05 MV to 4.5 MV. We have already run at this voltage for over two months in run 5.

• Scrub the rings and start delivery before Christmas

• Attempt to install the 90 deg lattice in early January as soon as we have high currents in the rings

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Overall run 7 plan

• Get to peak performance as soon as we can– All major MDs early in the run– Discover our limits quickly – being careful!

• Very few small MDs after April 1. We will still want to characterize the machine regularly (2 hrs every other week)

• Steady running as soon as we can with gradual improvements (tuning, raising currents if possible, etc.)

• We must keep a close eye on our delivery efficiency. Too many beam aborts can really hurt.

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LER RF 4.5 MV HER RF 16.5 MV

Delivery starts as soon as we get to about 4 x 1033 with high but acceptable backgrounds

Lumi goal of 8 x1033

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Put in 90 deg lattice and try very hard to make it stick

Raise LER RF to 5 MV

Lower βy*s

Raise HER RF to 17 MV if the above did not stick

Emittance tuning


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Try to get in the HER 90 deg lattice again

Continue to raise beam currentsRaise HER RF to 17.5 MV


Raise LER RF to 5.5 MV?Lower βy*s

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Continue to raise beam currents

Raise HER RF to 18.0 MV?

Lumi goal of 15 x1033Lower βy*s

Emittance tuning

Continue optics studies

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MDs

• Some MDs planned– Install 90 deg lattice early to see if we can

run with it– Specific attempts to improve the coupling

in the LER– Lower the βy

*s – may try this during delivery but then will want to measure results

– Specific attempts to increase beam currents (RF and feedback MDs)

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Running off the 4S

• We expect BaBar to want to run off resonance for some of the time as usual

• The collaboration is also considering running somewhere other than the 4S resonance for some fraction of the time– A possible candidate is the 3S– We have run on the 3S briefly in 2002 doing a quick energy

scan (24 hr). We lowered the HER beam energy.– Running on the 3S for some time should not be at all

difficult. It was easy to get to the 3S Ecm.– Another candidate is the 2S– Although we have not lowered the HER beam energy that far

we do not anticipate an difficulties is being able to do so

• We will want to schedule any off resonance running once we find out what the collaboration wants to do (not too early and not too late)

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Summary• Although Run 6 had a slow start we did manage to break most of our

luminosity records

• We uncovered a major problem with the flex flange RF seals in the HER and are addressing this issue this downtime. We are certain this will reduce the beam abort rate.

• The permanent magnet skew quads for the LER were installed and although we have seen some luminosity improvement we are hopeful we can gain more from this upgrade

• We have ambitious luminosity goals for Run 7. Shortening the beam bunches will let us lower βy*s. That and raising beam currents are our two major plans for increasing the peak lumi. Reducing the number of beam aborts is the other half of the plan to increase integrated lumi numbers.

• We will have to be cautious in our attempts to increase peak lumi. A close watch over temperatures and vacuum will be needed as we shorten bunches and increase currents on our push for a higher peak

• We look forward to getting this machine to really perform before we turn off next October

1 PEP Status M. Sullivan MAC Review Nov. 15-17, 2007 M. Sullivan for the PEP-II Team Machine...

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