KEKB Achievement & CrabsDec. 15 2010

Y. Funakoshi for the KEKB commissioning group

Achievements of KEKB

KEKB operation finished at 9:00 a.m. June 30th 2010

KEKB B-Factory

World-highest Peak Luminosity2.11 x 1034cm-2s-1 Twice as high as design valueWorld-highest Integrated Luminosity Total: 1040fb-1 as of June 30th 2010Skew-sextupole magnetsThe KEKB operation was terminated at the end of June 2010 for the upgrade toward SuperKEKB.

Finally two crab cavities were installed in KEKB,one for each ring in January 2007HER (e-, 8 GeV)LER (e+, 3.5 GeV)..after 13 years R&D from 1994

skew-sextupoles1040

KEKB Crab Cavities

Structure of KEKB Crab CavityTop ViewCrab mode: TM110: By on beam axisLower mode: TM010: dumped through coaxial couplerSquashed cell shape to split TM110 modes

Single Crab Cavity scheme1 crab cavity per ring.Saves the cost of the cavity and cryogenics.Beams tilt all around the rings. -> z-dependent horizontal closed orbitTilt at the IP:

RingLERHERfx22mradbx*1.21.2mbxC51122nx0.5060.511Dyx/2p0.250.25VC0.971.45MVwRF/2p509MHz

Motivation for Crab Cavities at KEKB

Beam-Beam SimulationsHead-on (crab) Crab Crossing can boost the beam-beam parameter higher than 0.15 ! (K. Ohmi)22mrad crossing angleStrong-strong beam-beam simulationAfter this simulation appeared, the development of crab cavities was revitalized. With the crab crossing, the beam-beam parameter and then the luminosity would be doubled !!

Improvement of Luminosity with Crab Cavities

Ohmi et al. showed that the linear chromaticity of x-y coupling parameters at IP could degrade the luminosity, if the residual values, which depend on machine errors, are large.

To control the chromaticity, skew sextupole magnets were installed during winter shutdown 2009.

The skew sextuples are very effective to increase the luminosity at KEKB.

The gain of the luminosity by these magnets is ~15%.

Chromaticity of x-y coupling at IP

Effectiveness of skew-sextupole magnets (crab on)

Effectiveness of skew-sextupole magnets (crab off)

Specific luminosity (crab on/off)Luminosity improvement by crab cavities is about 20%.Geometrical loss due to the crossing angle is about 11%. with skew sextuples

Beam-beam parameter (crab on/off)

Crab onCrab offRL0.8280.763Rxy(HER)1.150.993

Calculation of beam-beam parameterReduction factor for beam-beam parameter

2 sources of reductionhourglass effect and finite crossing angle

Montagues factor

Calculation of beam-beam parameter [contd]Reduction factor for luminosity

Luminosity

We use calculated values for x* and calculate y* and y0 from observed luminosity.

Effectiveness of crab cavitiesThe crab cavities at KEKB did work and brought the luminosity increase by ~20%. This is larger than the geometrical loss (~11%) due to the crossing angle.The highest luminosity with crab is 2.1 x 1034 cm-2s-1.Skew-sextupolesIncrease of HER beam current by solving the physical aperture problemThere still exists a large discrepancy between the luminosity achieved and the beam-beam simulation.The simulation predicted that the luminosity would be doubled.Side effects of large tuning knobs to compensate the machine errors?We will have no opportunity to investigate the reason for this.

Some Experience of Beam Operation with Crab Cavities

*Crab system AdjustmentCrab voltageCalibrated from klystron output power and the loaded Q value.The measurement to change the phase using beam also gives an independent calibration of the voltage.Both are in good agreement within a few percent.In addition, a crab voltage scan is done to maximize the luminosity in the luminosity run.Crab phaseThe reference phase is searched to minimize the beam orbit difference between the crab on and off, so that the bunch center is not kicked by the crab voltage.In the high-current operation, the phase is shifted by 10 degrees from the reference phase to cure the oscillation observed at high-current crab collision.Field center in the cavitySearched by measuring the amplitude of the crabbing mode excited by a beam when the cavity was detuned. A local bump orbit was set to adjust the beam orbit on the cavity axis.K. Akai

Phase 0174.8 deg.Vcrab set:1.0MV, estimated: 0.987MV agree very well crabHorizontal orbit by crab kick

Horizontal kick by crab cavity (rad)(Estimated from orbits around the ring)crabH. Koiso, A. MoritaCrab Phase Scan (LER)To find the zero-cross point of crab Vc, the crab phase scan is done.

An example of crab Vc scan

*Oscillation of High-current Crabbing BeamsA large-amplitude oscillation was observed in high-current crab-crossing operation in June 2007.It caused unstable collision, short beam lifetime and luminosity degradation.The crab voltage and phase were modulated at ~540 Hz. A horizontal oscillation of beams was also observed at the same frequency. None of the beam orbit feedback systems is responsible, since their time constants are 1 to 20 sec, much slower than the oscillation.The oscillation occurred when the LER tuning phase migrated to the positive side. This gave us a hint to understand the phenomena.Beam-beam kick is shaken.K. Akai

*A Remedy for the Oscillation was found.Observations at a machine studyThe oscillation occurred only with high-current colliding beams: it never occurred with a single beam, even at a high current. Both beams oscillates coherently.The threshold for the oscillation is dependent on the crab phase and tuning phase (see left).Cause and remedyWe concluded that the oscillation is caused by beam loading on crab cavities together with beam-beam force at the IP (see, next slide).We found that it can be avoided by shifting the crabbing phase by +10 and controlling the tuning offset angle appropriately.Dependence on the crab phase and tuning phase.Beam current was 1150 mA (LER) and 620 mA (HER).K. Akai

*Possible mechanism of the oscillationK. Akai

Physical aperture issuesLarge mis-alignment?We found that the field center of the HER crab cavity is ~6.5mm deviated from the BPM center.Effect to beam lifetimeIn case of beam collision, we found that the beam lifetime was determined by the physical aperture around the crab cavity for both beams at high bunch currents.In KEKB, the dynamic beam-beam effects (dynamic beta and dynamic emittance) are very serious.We tried to raise the crab voltage by lowering He temperature. However, this trial was not successful.We could mitigate this problem by enlarging the bx* from 0.9m to 1.2m. By doing this, we could increase the HER beam current. This brought some increase in the peak luminosity.

Aperture survey around HER crabScan of HER Crab Alignment BumpOriginal bump height: ~-6.5 mm necessary to minimize the beam loadingHigher bumps made the lifetime longer (peak at a bump with x = ~ -4mm). Mis-alignment of HER crab cavity?After the machine was shutdown, we actually found a mis-alignment of the HER crab cavity which is consistent with the original bump height.Necessity of the additional 4mm bump is still a mystery. 10Crab CavityAlignment BumpI+ x I- ~1.5mA2Life peakoriginal height~ 4mm

LER dynamic- and emittanceHorizontal beta function at IP

LERHERBetas with dynamic beam-beam effectcrabcrabwith/without beam-beam effects

CAVITY VOLTAGE DROP OF LER CRAB*Y. YomamotoCavity voltage of LER Crab was better than HER at horizontal test.But, after installation to beam line, it dropped gradually.And, it dropped suddenly from 1.3 to 1.0MV in Mar/17/2007.black dayThe sudden drop of LER crab voltage has never recovered until the end of KEKB operation.

DateCavity voltage [MV]CommentDec/20061.9horizontal testFeb/19/20071.5at beginning of beam commissioningFeb/22/20071.3maintenance dayMar/17/20071.3 1.0suddenly droppedMar/23/20071.1after thermal cycleMay/22/20081.2slightly recoveredJun/30/20081.3after pulse conditioningDec/18/20091.3not more recovered

Y. Yomamoto

LOWER TEMPERATURE OPERATION*PKlyVkickHe Temp.He LevelHe press. at cavityHe press. at pumpHosoyama-sans group tried lower temperature operation than 4.2K.

First trial was done in autumn/2008.It failed due to unexpected oil reduction of pumping system.

Second trial was done in spring/2009.Lower temperature operation was successful!The operation was stable around 3.6K.

But, performance of LER Crab cavity was not recovered.Y. Yomamoto

Y. Yomamoto

*Orbit Control and Feedback near Crab CavitiesDependence of RF power on the loaded Q value and a horizontal beam orbit for a beam current of 2 A.We have chosen QL=1~2 x105 for a good compromise. This value is suitable for operating the system with a possible error of X=1mm, andA high power source of 200 kW is sufficient for conditioning the cavity up to 2 MV.Typical parameters for the crab crossing. Orbit feedback around crab cavitiesOnly horizontal orbit feedback is considered.4 horizontal steering magnets to make an offset bump for each ring4 BPMs to monitor the offset at the crab cavity. 2 upstream (entrance) BPMs and 2 downstream (exit) System speed (design)

RF Trips of Crab Cavities*HER : 1.3/dayLER : 0.5/day558days2.8/day0.4/day0.8/day0.1/dayPeriod 1 : Feb/2007~Jun/2007, Period 2 : Oct/2007~Dec/2007, Period 3 : Feb/208~Jun/2008Period 4 : Oct/2008~Dec/2008, Period 5 : Apr/2009~Jun/2009, Period 6 : Oct/2009~Dec/2009Total averageRF trip of LER Crab was very small last year.Y. YamamotoLower crab Vc (HER)1.4 -> 1.3MV

Crab Cavity I/L System*Y. YamamotoBreakdown detectorVacuumTemperatureArc sensorHe pressure/levelRF output from pickup probesFlow rate of cooling waterCrab RF OffBeam abortBreakdown detector judges whether Pkly, VC and crab (only VC for LER) are normal, or not.If not, Crab RF is switched off.This is the most frequent cause of Crab RF trip.Whenever Crab RF is switched off, the beam is aborted coincidently, because of safety.Several pickup probes are attached for monitoring the transmit power and the RF output at coaxial beam pipe.Most of cases of HER trips are breakdowns of superconductivity due to discharge in the cavity. On the other hand, causes of LER cavity are discharge in the coaxial coupler or at the input coupler.

Y. Yamamoto

What happens in case of Crab RF Trip?1. D11-F klystron out 2. D11-F cavity voltage 3. D11-F cavity tuner phase 4. HER DCCT RF offBeam AbortTypical example when HER Crab RF trips.HER beam current: 750 mAWe abort the beam and switch-off the crab RF in case of crab RF trip.20090422 7:38 HER Vc abortBeam positions of aborted beamreferenceIn some cases, the beam is kicked more largely by the crab after RF trip and before RF off.One of my colleagues (Nakanishi) are studying the transient behavior of the beam.Y. Morita

RF phase shifts 50 degree in 50 sec after the RF stop

-> Nakanishis talk (tomorrow)

*Phase stabilitySpan 200 kHzSideband peaks at 32kHz and 64kHz.Span 10 kHzSpan 500 HzSideband peaks at 32, 37, 46, 50, 100 Hz.Spectrum of pick up signal is consistent with phase detector data.Phase fluctuation faster than 1 kHz is less than 0.01, and slow fluctuation from ten to several hundreds of hertz is about 0.1. They are much less than the allowed phase error obtained from the beam-beam simulations for the crabbing beams in KEKB.According to b-b simulation by Ohmi-san, allowed phase error for N-turn correlation is 0.1N (degree). Spectrum around the crabbing mode measured at a pick up port of the LER crab cavity. Beam current was between 450 and 600 mA.Phase detector signal. Beam current was 385mA (HER) and 600 mA (LER).K. AkaiRogelios Talk (tomorrow)

Measurements or experiences on impedance related issuesThe following measurements were done before and after the installation of crab cavities (by T. Ieiri).Bunch current dependence of coherent tune shiftLoss factorBunch lengthening as function of the bunch currentNo significant difference was observed on these measurements between before and after crab.We once observed a coupled bunch instability due to the crabbing mode. However, this was due to wrong setting of the detuning frequency.As for the HOMs or LOMs, we have not experienced that they induced any coupled bunch instability.

Crab Vc scanThe scan was done in HER on Dec. 24th 2009.The beam current was 800mA (single beam).The crab voltage was changed from 1.4MV to 0.5MV and from 0.5MV to 1.4MV.No beam loss and change of beam sizes were observed.

Toward SuperKEKB

SuperKEKBWe have decided to change the design concept of SuperKEKB from the High-Current scheme to the Nano-Beam scheme (Italian scheme) at the beginning of 2009.No crab cavities will be needed for SuperKEKB with the Nano-Beam scheme.

Reasons for change of schemeHigh-Current to Nano-BeamLuminosity gain with crab cavitiesThe beam-beam parameter of 0.15 which was predicted by the beam-beam simulation was not achieved.Difficulty of CSRWe need travelling focus scheme to achieve the design luminosity with the high current scheme.IR designNo solution for realistic IR design with bx* = 20cm was found.Budget constraint

Comparison of parameters1 (Oku-Yen) = 1.23 M USD = 0.88 M EUR (as of 6 Nov., 2010)

KEKB DesignKEKB Achieved: with crabSuperKEKBHigh-Current SuperKEKB Nano-Beam Energy (GeV) (LER/HER)3.5/8.03.5/8.03.5/8.04.0/7.0bx* (cm)30/30120/120 20/203.2/2.5by* (mm)10/105.9/5.9 3/60.27/0.31ex (nm)18/1818/2424/183.2/4.3~4.6f(mrad)1111 -> 0 (crab)15 -> 0 (crab)41.5xy0.0520.129/0.090 0.3/0.510.089/0.083sz (mm)4~ 65/36/5Ibeam (A)2.6/1.11.64/1.199.4/4.13.6/2.6Nbunches5000158450002503Luminosity (1034 cm-2 s-1)12.11 5380Cost (Oku-Yen)499304Power (MV)459571

Beam pipes (LER)FY2010FY2011FY2012FY2013FY2014FY2015Beam pipes (HER)Magnets & Power suppliesTunnel clearBeam monitors and ControlIR hardwareRF systemMR commissioningKEKB operationSuperKEKB Main Ring scheduleOct. 20, 2010InfrastructurePhysics RunK. AkaiDismantlement of the LER ring started in this autumn.

SummaryThe crab cavities at KEKB have been working much more stably than the initial expectation.They have been used in usual physics run.The crab cavities at KEKB did work in the sense that the luminosity gain with the crab cavities is much larger than the geometrical loss due to the crossing angle. There still exists a large discrepancy between the beam-beam simulation and the experiment with the crab crossing.We have 3-years experiences of the beam operation with crab cavities and hope that these experiences are useful for other laboratory .The KEKB operation was terminated at the end of June 2010.In SuperKEKB, we will not employ the crab cavities.The budget of SuperKEKB has been partially approved and we started the construction of SuperKEKB.

Spare slides

Cost estimation (Accelerator part)1 (Oku-Yen) = 1.23 M USD = 0.88 M EUR (as of 6 Nov., 2010) Cost for Belle upgrade is not included in the list.K. Akai

ComponentsCost (Oku-Yen)RemarksLinac upgrade and Damping Ring40RF electron gun, positron capture section and L-band acc.,Damping Ring components, cooling systemVacuum System103beam pipes (ante-chambers, electrodes, etc), pumps and other vacuum components, cooling systemMagnet System71magnets, power supplies, cables, cooling systemIR upgrade14QCS and other IR hardwareRF System21reinforcement of RF stations, improve cavities and rearrangementBeam monitor and control31BPM, SRM, feedback, control system, etc.DR tunnel and buildings24DR tunnel, buildings for Linac upgrade, DR and MRTotal304

Approved budgetDamping ring: 5.8 Oku-Yen (FY 2010)Special budget (Saisentan-Kiban-Jigyou): 100 Oku-Yen (3-years from FY 2010)Beam pipes for positron ring (57 Oku-Yen)Magnet system for positron ring (43 Oku-Yen)

Beam pipes (LER)FY2010FY2011FY2012FY2013FY2014FY2015Beam pipes (HER)Magnets & Power suppliesTunnel clearBeam monitors and ControlIR hardwareRF systemMR commissioningKEKB operationSuperKEKB Main Ring scheduleOct. 20, 2010InfrastructurePhysics RunK. AkaiDismantlement of the LER ring started in this autumn.

Tunnel & buildingBeam pipesMagnets & Power suppliesFY2010FY2011FY2012FY2013FY2014FY2015RF SystemLinac upgrade and DR construction scheduleMonitors, ControlLow emittance e- gune+ new matching & L-band acc. Damping RingLinac upgradeDR commissioningOct. 20, 2010Beam transport and kickersLinac commissioningPF injectionStudy (A1 gun)3T3-2TK. Akai

25 SuperKEKB luminosity upgrade projectionShutdownfor upgradeIntegrated Luminosity(ab-1)Peak Luminosity(cm-2s-1)Goal of SuperKEKBYear9 month/year20 days/monthCommissioning starts mid of 2014We will reach 50 ab-1around 2020.Y. OhnishiWe are here25

Beam Abort Delays* Beam Abort requestBeam Dumping System waiting for beam gap max 10st3

D. Zhou, K. Ohmi, Y. Seimiya, Y. Ohnishi

Definition of x-y coupling parameters (SAD notation)Normal (decoupled) coordinateUsual coordinate

Measurement on chromaticity of x-y coupling at IP (HER)blue: without skew-sextuplesred: with skew-sextuples

Examples of R-chromaticity scan

Balance of crab kick strength between HER and LER can be tested by measuring the horizontal offset with the same amount of the crab phase shifts.Crab phase of LER and HER were changed by10: The horizontal offset at IP (beam-beam kick) changed by15m. (1) ideally zero)Change LER phase only by1 or HER only by1 brought offsets of 16~19m.(2) calculated value from crabbing angle is18m.When we changed HER crab Vc from 1.55 to 1.43MV, the horizontal offset did not change with the same 10 phase change.(3) Crab phase vs Horizontal beam-beam kick(1)(2)(3)0.94MV (LER)1.43MV (HER)0.94MV (LER)1.55MV (HER)

High beam current operation with crab detunedMachine timeWe tried twice (April and June 2007).Beam currentsWe stored the same beam currents as before crab.LER: 1700mA, HER: 1350mAAchieved luminosity11.16 /nb/s 16.4 /nb/s before cabno enough time for tuningCrab situation (No serious problems were found.)No crab tripsHeating of coaxial parts (LER, HER)Temperature alarm -> We could manage to reinforce the cooling power.HER LBP HOM absorber temperature alarmOnly alarm -> Reinforcement of cooling power afterward.Coupled bunch instability due to crab modeDetuning frequency was wrong. -> Re-tuning of detuning frequency.

*High current: improvements in JuneVacuum pressure in the cavity before and after the warm up. Temperature at the inner conductor of the coax before and after the reinforcement of the cooling power of the LER cavity.K. Akai

High current(Crab ON)High current(Crab ON)High current(Crab detuned) Crab warm-up

Crab ON high currentsCrab detuneHigh currents700mA1300mA1700mA1350mA10.602 /nb/s11.156 /nb/sCrab ON high currents

HOM LOAD AT HOM DAMPERSCrab cavity has two ferrite HOM dampers.There are two SiC dampers at downstream of LER Crab cavity.They are also effective for damping HOM load generated in Crab cavity.SiC2 damper was introduced for reduction ofHOM load absorbed at SiC1.*The 15th KEKB Accelerator Review CommitteeY. MoritaLBPLBPCoax.Coax.HERLERSiC dampers

Load (kW)Tmax ()Flow (/min)k (V/pC)HER 1250 mACoaxial3.034.05.00.28LBP6.940.07.00.74LER 1700 mACoaxial2.531.35.00.13LBP12.447.27.50.68SiC113.039.113.00.72SiC212.241.510.30.66

The 15th KEKB Accelerator Review Committee

CRAB VOLTAGE SCANNING*The 15th KEKB Accelerator Review CommitteeVoltage scanning is sometimes carried out as part of beam tuning for higher luminosity.

During this operation, RF trip of Crab cavity occurs frequently.

Very careful operation is necessary!

When Crab RF is switched off, RF conditioning is sometimes done at local control room.Max. operation voltage

DateLER [MV]HER [MV]Feb/29/20080.83 0.881.37 1.41Mar/4/20080.88 0.881.37 1.38Apr/5/20080.83 0.841.38 1.39Apr/15/20080.84 0.851.39 1.40Apr/25/20080.83 0.83Jun/4/20080.83 0.851.45 1.46Jun/18/20080.83 0.83Oct/26/20080.85 0.831.37 1.34Nov/22/20080.83 0.811.50 1.48Dec/18/20080.81 0.84Apr/26/20090.85 0.831.35 1.32May/20/20090.83 0.851.32 1.33Jun/6/20090.85 0.861.33 1.37Jun/18/20090.95 0.981.50 1.55Nov/2/20090.87 0.901.29 1.34Dec/12/20090.95 0.971.40 1.45

The 15th KEKB Accelerator Review Committee

PIEZO ACTUATOR BREAKDOWN*The 15th KEKB Accelerator Review CommitteeILERPKlyVkickMain PositionTunerLoadVPiezobreakdown@10:53Crab cavities have been operated without Piezo actuator during most of beam commissioning.

Low level feedback system can control Crab cavity without Piezo.Not significant!

DateCavityCommentJun/9/2007LERAt RF recoveryJun/23/2007LERAt beam abort with RF tripOct/1/2007HERAt RF recoveryOct/4/2007HERAt RF tripOct/16/2007LERAt RF recoveryOct/15/2008HERAt RF tripMay/15/2009LERAt beam abort with RF tripJun/11/2009HERAt beam abort with RF tripOct/25/2009LERAt beam abort with RF trip

The 15th KEKB Accelerator Review Committee

*Effect of Transient Beam LoadingRevolution periodBunch trainGaptPhase: length of bunch train: Gap lengthD. BoussardT0T. IeiriThe beam gap transient brings phase differences for bunches in the bunch train.Due to this, each bunch sees a different crab phase and then a different H-COD.In the KEKB case, this COD difference amounts to about 0.2sx at the IP.Fortunately, the effects of the two beams cancel each other and so almost no luminosity degradation is brought by this effect.

*Measurement on Phase and Orbit Shift along TrainZLER / 1530mAHER / 800mAN=1585XT. Ieiri~0.2sxCrab ON3.06 bucket spacing

Evidence of Crabbing Motion (1): Streak Camera

HER crabbing anglemeasurement and calculationcalculation @ streak cameracalculation @ IP

*Evidence of Crabbing (2): Beam-Beam DeflectionBunch Current: 0.73/0.42 mABunch Current: 0.64/0.47 mA HER current was lost from 15 to 13.5 mA during scan.Crab ON ( Vc = 1.31/0.92 MV)Crab OFF Horizontal effective size at IP reduces to 72% by the crab.x_x=00=167 +/- 3 m (ON)x L/H=18/24 nmx_x=11=230 +/- 3 m (OFF)Ratio of Slope:T. Ieiri

*Method of Measurement of Beam-Beam Kick

Beam-beam Kick (Rigid Gaussian) Beam-Position Change measured at a detector Effective Horizontal Size at IPBy Fukuma & Funakoshi

x: Horizontal OffsetMissing partner method:Orbit difference of collision and non-collision bunchesT. Ieiri

*Calculation of Beam-Beam Kick with and without Crossing AnglexzUse code BBWS by Ohmi How to calculate the kick with an angle of 22 mradx=24 nmHead-onCrossingSlope in Linear RegionResult: The measurement is consistent with the calculation. A particle is horizontally moved and the kick data are summed up, including the longitudinal profile.T. Ieiri

Betas with dynamic beam-beam effectbefore summer 2008 x*= 0.9m fall 2008 x*= 0.9mcrabcrabwith/without beam-beam effects

*****