The Eighteenth KEKB Accelerator Review Committee Report
March 6, 2013
Introduction
The Eighteenth KEKB Accelerator Review committee meeting was held on March 4-7, 2013.
The following members of the committee were unable to attend: Stuart Henderson Miguel
Jimenez, and Frank Zimmerman. Nadine Kurita (SLAC) attended as an expert in lieu ofMiguel Jimenez. Appendix A shows the present membership of the committee. The meeting
followed the standard format, with two days of oral presentations by the KEKB staff
members, followed by discussion between the committee members. The Agenda for the
meeting is shown in Appendix B.
The committee was impressed by the enormous progress in the construction of SuperKEKB
and, as always, by the high standard of the presentations. It was particularly pleasing to havesuch excellent presenters including many junior staff members. The committee evaluated thepresent status of the project and prepared recommendations, which were presented to the
KEKB staff members before the close of the meeting. The committee wrote a draft reportduring the meeting that was then improved and finalized by e-mail among the committee
members. The report is available at http://www-kekb.kek.jp/MAC/.
Contents
A) Executive SummaryB) RecommendationsC) Findings and Comments
1)
Overview of Ring Construction Status and Schedule2)
Belle II Construction and Schedule3)
Beam Dynamics Issues in SuperKEKB
4)
Optics Issues
5)
Magnet Overview
6)
Magnet fabrication and field measurement
7)
Magnet Power Supplies
8)
IR Magnet
9)
Construction of the Interaction Region
10)
Beam Background
11)
Collision Feedback (dithering)
12)
Vacuum Construction Status and Schedule
13)
TiN Coating and Baking
14)
Collimator
15)
Normal-conducting cavities for MR and DR
16)
Superconducting cavity
17)
Improvement of LLRF system
18)
KEK Roadmap
19)
SLAC-KEK Collaboration
20)
Overview of Injector Construction Status and Schedule
21)
RF Gun22)
Alignment and Support
23)
Positron Source
24)
Flux Concentrator Modulator Development
25)
Commissioning of Electron Beam

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26)
27)
28)
29)
30)
31)

New Transport Line for PF-AR
The Damping Ring, Transfer Lines, and HER Abort System
Beam Diagnostics
Estimation of Beam Loss
Controls
Ring CommissioningA) Executive Summary
The SuperKEKB Project has made exceptional progress since last year. The development,
fabrication and installation of SuperKEKB Main Ring components have progressed well,including beam pipes, magnets, wigglers, magnets power supplies, RF cavities, klystrons,
LLRF system, diagnostics and controls. The Damping Ring is also progressing smoothly; thedesign and fabrication of its components, magnets, RF cavity, vacuum system, injection
system, instrumentation and controls are well advanced. Injector upgrades are proceeding onschedule with a notable accomplishment on the RF gun.
Solid progress has been made in the design and fabrication of the Interaction Region and its
associated components such as the superconducting QCS magnets and vacuum chambers.
However, the construction of the Interaction Region, including the installation of all thecomponents, still remains on the critical path for SuperKEKB to start commissioning withBelle II.
The design and construction of the Belle II detector has also made considerable progress.
The most important outstanding item is the TOP detector, which could delay the move-in of
the detector.
There still remain some discrepancy between the linac alignment methodologies, and the ringalignment is seeking the best strategy to mitigate the slow, but inevitable, settling of part of
the ring (~2mm per year).
The Main Ring commissioning plan was presented and the detailed three-phase plan iscredible and takes account of all of the constraints. Two options were presented: the first
assumes that the detector and interaction region components are ready on the present
schedule. The second changes the commissioning order to enable progress in case either thedetector or the interaction region components are delayed. The linac commissioning plans
are being developed and will be presented at the next Review.
Overall, the committee considers the technical cost for the entire Project to be on track, butthere are still concerns about timely funding. The technical and schedule risks are considered
low for the Injector chain, facilities and the ring components, but the committee considers thetechnical and schedule risk high for the Interaction Region. The committee is pleased that a
mitigation strategy has been developed, which has been included in the commissioning plan.
The alternate plan also enables the project to initiate beam commissioning in JFY14, as
required by the funding agency.
B) Recommendations: The committee has made recommendations throughout
the different sections below.
Highlights of these recommendations are
summarized here.
1) Despite the strong support of KEK management to increase staffing, including a few
new junior hires and rehiring senior, experienced retired staff, shortage of qualified staff

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continues to be a major risk to successful completion of the project, the commissioning
and operations.
2) Develop and track to a clear set of milestones for the production of the IR SC magnets,
cryostats and the other IR components so that progress can be carefully monitored andthe high schedule risk, which concerns the committee, can be mitigated.
3) Continue the ongoing work aimed at the development of necessary simulation tools, withbenchmarking, to study various critical path beam dynamics effects impacting
SuperKEKB performance. These simulations should include at least the 3D IR modeling,error effects, dynamic aperture, beam-beam interaction, space charge, intrabeamscattering, and the outcome figures of merit including the achieved luminosity, detector
background, and Touschek lifetime. International collaboration should be enhanced touse the experience accumulated in the sister laboratories.
4) Continue the detailed evaluation of all sources of beam-induced background to identify
and mitigate the major loss terms in the detector to prepare for shielding; this includes
the impact of the additional weight on the QCS support system.
5) Continue to aggressively pursue the timely completion of the components of the injector
chain while maintaining the ability to simultaneously inject into the PF and AR.
Complete hardware demonstrations of key components and simulations with the goal ofa self-consistent start-to-end description of the injection system that meets all of therequirements.

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C) Findings and Comments
1) Overview of Ring Construction Status and Schedule
The KEKB team has made extremely good progress in the ring construction since the last
review. The design of the main ring has been improved based on an optimization of theInteraction Region. The development, fabrication and installation of SuperKEKB Main
Ring components has progressed well under consistent project planning, including beam
pipes, magnets, wigglers, magnets power supplies, RF cavities, klystrons and LLRF
system. The Damping Ring is also progressing smoothly, the design and fabrication of
the components, magnets, RF cavity, vacuum system, injection system, instrumentationand control system, are also well advanced.
Although the project schedule is aggressive, the master schedule of the SuperKEKB isbased on realizable and feasible plans. The schedule optimization of fabrication,
installation and integration for the all of the SuperKEKB accelerators has been done in avery efficient way leading to the planned completion of the target project milestone ofcommencing the commissioning by the end of JFY2014. The construction andcommissioning schedule of the Damping Ring is arranged in parallel with KEKB to beready to complete the Phase I and Phase II commissioning requirements.
The SuperKEKB Commissioning Scenario is clearly defined and well developed in threephases, which greatly optimized resource utilization for fabrication, installation andcommissioning in the project schedule and ensures achievable performance.
Tremendous and impressive progress has been made in the design and fabrication of theInteraction Region and its associated components such as the superconducting QCS
magnets and vacuum chambers. However, the construction of the Interaction Region,
including the installation of all the components, still remains on the critical path forSuperKEKB to start commissioning with Belle II.
The project team shows very complementary capabilities with hard work of the staff andstrong support of KEK management to increase the staffing, including rehiring senior,
experienced retired staff. However manpower resources is still a limiting factor for
SuperKEKB to be completed on its aggressive schedule. The committee supports thecontinuing efforts to ensure that sufficient staff is made available for the SuperKEKB
construction and operation needs.
Recommendation
There are number of components which must be systematically checked for their impact
on the impedance budget. It is recommended that a single person be assigned as the“impedance police” responsible for checking and controlling every component which has
an impedance contribution to MR.
2) Belle II Construction and Schedule
The construction of Belle II is going well. The design phase is approaching the end. The
detector had to be rotated about a vertical axis to match the new geometry of theaccelerator. The rotation process is nearly complete. The PXD detectors have beensuccessfully modified to accommodate the timing changes of the accelerator bunches tominimize dead time from noise. The SVD detector is in the final mockup phase. The
CDC is in production.
The critical path of the the project now goes though the TOP modules being contributedby the US contingent. Several reviews have taken place and new modifications of the

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modules are being tested. The production of the quartz bars is under review. A US-DOE
CD review of these modules will be held in August. The lifetime of the TOP
photomultiplier cathodes from radiation is being studied and a method of replacing thetubes quickly is being investigated.
The luminosity monitor used by both the detector and the accelerator is being producedby the Belle II collaboration. The final details of this monitor needs to be agreed on by
the accelerator group so that the SuperKEKB Accelerator Group can complete theinteraction point and luminosity feedbacks.
Recommendation:
The Belle II TOP detector is on the critical path. Constant attention should be paid to thisdetector component. Other possible mitigations for the TOP issues should be investigated.
3) Beam Dynamics Issues in SuperKEKB
In line with recommendations of the previous ARC, beam dynamic effects of criticalimportance for the SuperKEKB performance were investigated in greater detail.
Coherent Synchrotron Radiation (CSR) simulation was performed for both DR and mainrings. The KEK-SLAC collaboration resulted in benchmarking 5 available codes forevaluation of CSR impedance, wake and Microwave Instability (MWI). Comparison ofalternative approaches helped to rule out computational artifacts and produce morereliable results.
In DR, the optics has been optimized for CSR, yet the MWI threshold is likely to bereached, resulting in sizable bunch lengthening. In LER the MWI threshold is predicted
to be exactly at the maximum design bunch intensity, while in HER a safety factor of 3 isreported.
In the weak-strong beam-beam simulations, machine nonlinearities of the current optics
model are included. The tune scans revealed enhancement of synchro-betatronresonances and more stringent limitations on the working point choice. The currentdependent roll-off of the specific luminosity becomes stronger, accompanied bystrengthening of the high-order resonances in the tune map. Optimizing the nonlinear
lattice for a larger dynamic aperture leads to a better luminosity performance. Thisobservation leaves a hope that the specific luminosity can be recovered in operation bytuning the real lattice for a better lifetime.
Importance of the chromatic coupling compensation was re-confirmed and the machineparameter tolerance table (relevant to a prior-year optics model) was updated for residual
chromatic coupling at the 10% luminosity loss.
In the NanoBeam scheme the space-charge effect turned out to be a new serious problem;
its interplay with the beam-beam effect became a novel simulation subject. Preliminary
results show the vertical beam-beam and space-charge tune-shifts in LER of the sameorder with no additional degradation of the specific luminosity.
The committee puts an emphasis on studying the space charge effect on the beam-beaminteraction in the SuperKEKB LER to see if the effects are as strong as early simulation
indicates. Possible mitigation techniques should be investigated.
The committee recommends that a comprehensive table be compiled, where the effects on
the beam-beam interaction and resulting luminosity are calculated for accelerator
operational errors such as a vertical offset at the IR, a vertical angle error at the IP, ahorizontal offset at the IP, a beam roll error, residual dispersion, coupling or chromatic
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coupling, all within the same optics model. Possible errors in the detector solenoid fields
should be studied for their effect on the beam-beam interaction. The most critical weakstrong simulation results should be checked in the strong-strong simulation.
The committee strongly supports the ongoing work aimed at the development ofnecessary simulation tools, with benchmarking, to study various critical path beam
dynamics effects impacting SuperKEKB performance. These simulations should include
at least the 3D IR modeling, error effects, dynamic aperture, beam-beam interaction,
intrabeam scattering, and the outcome figures of merit including the achieved luminosity,
detector background, and Touschek lifetime. International collaboration should beenhanced to use the experience accumulated in the sister laboratories.
4) Optics Issues
The design studies of the LER and HER magnetic lattices are very advanced. There havebeen many optics configurations created and studied for their respective advantages. The
arc optics seems to have settled down, being slightly updated with to minor modifications
to the detailed hardware design. The Beast optics is prepared for Phase 1 commissioning.
The overall ring and the IR optics have been studied mostly independently. The IR optics
is still in evolution following the improvements in the technical design of the final focus
magnets. Using the 3D IR model, the IR magnet error correction procedure is developedby simulation of the dynamic aperture capable of recovering the Touschek lifetime to~600 seconds. The right hand side of the final focus is still not fixed, where they aretrying to optimize the nonlinear corrector set. The two optics are now being merged into
a combined study to allow relative tolerance considerations. Maximizing the Touschek
lifetime and the dynamic apertures have been major goals of these studies.
The 20-mm vertical settling over half of the ring tunnel circumference and its impact onalignment is an important issue. Consequently, the machine effectively tilts as half of itsinks by about 2 mm per year. A decision by the magnet group has been made to keep
the rings aligned to this existing overall subsidence (trajectory). This removes the need tovertically move the RF cavity systems and reduce the risk of vacuum seal failure. Any
magnets with a large discontinuity in misalignment relative to its neighbors will be
adjusted locally. One option discussed by the committee that SuperKEKB may wish toconsider is biasing the overall magnet and vacuum chamber alignment upward a few mms
so that the HER and LER rings will have several years of movement before the settling of
the ring tunnels seriously degrade the machine’s flatness.
The overall interaction region IR will have 40 correction elements including dipoles, andnormal and skew moment correctors from quadrupole, sextupoles, skew octupole, andother higher order fields. All of these correctors will need to be adjusted to maximize theluminosity. The beam measurements and software controls to make decisions andcalculations how to adjust these variables are now just being investigated. It would be
ideal to develop an orthogonal set of adjusting variables using these 40 correctors to
optimize the luminosity as rapidly as possible. However, more likely the less attractive
possibility of combinations of non-orthogonal adjustments will be the outcome. This
would significantly increase the luminosity tuning time.
R1: The committee recommends concentrating on developing very detailed and robust
procedures for correcting the closed orbit and linear optics distortions caused by realistic
field errors, especially in difficult places like the local chromaticity correction section.
For the IR optics, an algorithm should be developed for the control-room operational
usage, aimed at improving the beam lifetime (and the dynamic aperture) by numerous

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nonlinear corrections, in addition to the blind downhill-simplex optimization.
R2: The Optics Group should continue to merge the IR and ring lattices with the intent tostudy optimized luminosity tuning with full IR fields, full error tolerances, all correctors,
and the needed small vertical emittances.
5) Magnet Overview
It is the middle of the busy period for the magnet program. Installation and survey havebeen progressing smoothly. More than 100 arc dipole magnets and 140 verticalcorrectors were installed and aligned. In some areas, the lattice is designed to be very
compact, which caused some difficulties in installation, which was resolved with proper
equipment. Some of the delivered magnets were mishandled or manufactured withdefects by the vendors, which incurred extra manpower to clean up the flaws.
The LER wigglers, 112 half-pole wigglers and 56 single-pole wigglers, were newly
installed in the Oho and Nikko sections and aligned. Some of these wigglers were packed
near the SC cavities in a straight section without much space for installation. The issue offield leakage in this section was stated to be similar to the previous KEKB installation.
Two teams carried out the alignment of the survey monuments in the Tsukuba IP areafrom different directions. The measured alignment error between the two groups when
they met at the center was within 0.1 mm, which is an excellent crosscheck of thealignment procedures. From the long-term alignment history, the floor in Fuji is sinking
2mm/year with some extra glitches due to the earthquake. It is suggest that themeasurement data of 2012 be used as an alignment reference to smooth out the ring,
including an allowance for future ground movement. The alignment information should
be discussed further with the Optics group to find best solution.
Tilting supports will be introduced to allow 30-degree tilts on 24 sextupole magnets,
necessitating the modification of existing KEKB sextupole magnets. More magnets will
be fabricated and installed in 2013. Major work in fabrication, field measurements,
installation, alignment, connecting cooling water and power supplies should be completed
this year. One expects that the magnet program will be continued in 2014.
The committee congratulates the magnet group for the huge amount of work
accomplished with extreme precision.
Recommendations
1. The skew quadrupole components will be built within the existing saturated sextupole
magnets using strip coils wrapped around the ion poles. Additional excitation current
will further saturate the magnets. Analyzing the non-linear components with full
excitation current of the skew quadrupole will be necessary to enable the effect on
beam optics to be evaluated.
2. The spaces between some of magnets or wigglers are very tight. The field leakage,edge effect of dipole magnets and the cross coupling between the tight spaced
magnets should be double-checked.
3. A similar situation occurred near the SC cavities area. It might be worth to remeasure the leakage field around the SC cavities area, comparing it to the field
leakage during KEKB operation.
4. It might be worthwhile for the optics group to evaluate the magnets measurement
results to see if sorting the magnets would reduce the strength of the correctors.

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6) Magnet fabrication and field measurement
There are now 138 arc dipole magnets, 168 wigglers, and 220 vertical correctors installedin the LER tunnel. The rest of magnets are either in mass production or in procurement.
The dipole field was measured by a 6-meter long flip-coil, which was calibrated by areference magnet after each measurement. The normalized field error distribution for the
109 dipoles is 1.1 x10-5. Damping wigglers are used in the main rings to reduce
emittance. These wigglers are measured by harmonic coils. The normalized standard
deviations are 1.49 x10-5 and 2.45 x 10-5 for half pole and single pole wigglers,
respectively. All these tolerances are acceptable.
The committee has some unanswered questions on the effects of cross and leakage fields
for these tightly packed wigglers and magnets. The measured results on these delivered
magnets should be provided to the optics group to include in the correction algorithms.
7) Magnet Power Supplies
The KEKB team continues to show progress in addressing the magnet power supply
needs for SuperKEKB. There are a total of 308 power supplies to be used forSuperKEKB. Of these 285 require a 20-bit resolution with corresponding stability of <20
ppm/day and a ripple of less than 10 ppm. The balance of 23 power supplies require 24bit resolution with a corresponding 10 times smaller stability (<2 ppm/day) and ripple (<1ppm). To achieve this 24-bit resolution, the KEKB team has come up with a system ofadding 16 20-bit DACs fed by a FPGA. It is not clear to the review committee how
successful this approach will be if the errors of the 20-bit DACs are not completely
uncorrelated. Similarly, the review committee does not fully appreciate the value of
having a resolution significantly less than the stability of power supplies (24-bit
corresponds to 0.12 ppm). Consequently, as was indicated in the 17th review report thecommittee remains cautious.
Recommendation
The temperature of the environment might also have considerable effect to the highperformance power supplies. The committee suggests that the team checks thecorrelation between the long-term drift of output current and temperature near control unit.
8) IR Magnet
Work continues on all aspects of the complex magnet systems of the Interaction Region(IR) and considerable progress has been made since the 17th KEKB Accelerator Review
committee meeting. In the area of IR Magnets and their associated cryostats there has
been an improvement in the cross sectional designs of all of the magnets since theprevious review, and very good results from the prototype magnets. Vanadium
permendur has been selected to be the yoke material for two magnets, QC1E and QC2P.
Three-dimensional design analysis has also been started in collaboration with BNL andadaptations have been made to the cryostats to lessen the coupling to vibration.
The QC1P and QC1E prototype magnets have been constructed and cold tested andmagnetically measured. The QC1E was powered up to 2.157 kA without a quench well
above the nominal operating point of 1.559 kA. The measured load lines have adequate
margin for both the nominal operating point and 12 GeV operating point. The measured
quadrupole field was 1% below the design. The QC1P was operated at 2.1 kA without aquench well about the nominal operating current of 1.625 kA, again with adequate load
line margins for both nominal and 12 GeV operation. Both prototypes produced within
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~±1% of the design value for the integrated quadrupole. Sextupole error moments were
present in both prototypes. Subsequent analysis of the source of these errors has resulted
in a number of areas with design refinements.
The choice of vanadium permendur for the yokes of two magnets to reduce the leakage
field is understandable. The size and shape of the yoke pieces are such that production in
vanadium permendur should not present too much additional difficulty. Analysis of thefull implications of the use of vanadium permendur is just beginning. The mechanicalproperties of vanadium permendur are significantly different from those of steel and iron.
Care must be exercised to no exceed the material properties in the design or to stress thematerial during fabrication or assembly. This is particularly important after the fullmagnetic anneal required to obtain the desired magnetic characteristics when themechanical properties are considerably changed.
The cryogenic system for the QCSL has been installed and cold tested. Nevertheless, thechallenges associated with the construction and installation schedule for the QCSL isextremely aggressive and acknowledged as being difficult to achieve. Although notpresented as such, the critical path of the SuperKEKB construction and installation
appears to run through the production, installation integration of the IR Magnets. No
remediation of the schedule risk was discussed in detail.
As stated in the 17th Review Report, the schedule for the completion of the magnets byearly 2015 is very aggressive and has no schedule contingency. This leads to a naturaltendency to move as quickly as possible from design development activities into
fabrication. As was recommended from previous reviews, a clear set of detailed
milestones and decision points with criteria based on performance requirements should bemaintained.
Overall, the IR magnets remain the area of highest risk for both technical and schedule.
Nevertheless, the SuperKEKB is proceeding well in this area.
Recommendation carried forward:
The committee recommends making a clear set of milestones and criteria-based decision
points for the development and fabrication of the IR SC magnets, corrector andcompensation coils, and cryostats so that progress can be carefully tracked and contingent
plans enacted in a timely manner if required.
9) Construction of the Interaction Region
The interaction vacuum chambers are challenging and KEKB has made significant
progress on their designs since the last review. The design of the inner IP chamber iscomplete and fabrication is underway and expected to be completed in 2013. The IP
chamber was prototyped and used to validate the feasibility of the various joint designs(Be-Ti Braze, Ti-Ta HIP, EWB near HIP). Note, the results of the prototype testing were
not presented.
Additional fabrication testing is planned for sputtering Au on Ti and other joining tests.
Some thermal and stress analyses have also been performed to validate the design and an
additional analysis is underway including dynamic analysis. The stress at the junction of
the HER and LER should also be examined due to thermal expansion differences in the
two legs.
The designs of the two chambers that are outboard of the inner IP chamber are advancing
and expected to be completed soon. These chambers incorporate ridges to reduce thebackgrounds in the IP. The steep ridges were analyzed and found acceptable for beam
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impedance. Fabrication of these chambers is scheduled from April 2013 to March 2014,
and is on schedule. The QCS chamber designs are still under development and thesechambers will be fabricated in 2014. The overall KEKB schedule shows that the IR
chambers are needed by the end of 2014, so there is not a lot of schedule contingency.
The background requirement in the IP has led to the need to achieve a low pressure in thisregion. The vacuum performance has been extensively studied, but the configurationnecessitates that vacuum pumps are a considerable distance from the interaction region(~4m) and so little can be done other than surface treatment to improve the vacuum, as it
is almost entirely conductance and outgassing (photon-induced) limited. Also the Auplated Ta chambers have been demonstrated to have photon-induced desorption rates
lower than copper. Photon-induced desorption testing was executed at the Photon
Factory to obtain realistic values and used to predict the vacuum pressures. The only
other alternative to improve the pressure would be to consider NEG coating of thesechambers, but this could lead to other issues (I2R and chamber lifetime). Also, the affecton the backgrounds from the vacuum pressure close to the IP is smaller than the effect ofthe pressure at about 10m away from the IP. The vacuum pressure beyond 5m was notdiscussed during this review. It would be useful to have a background budget to evaluate
the impact of the vacuum pressures in the IR region.
The commissioning plan of the KEKB Accelerator requires that two fairly separate andself-contained installations of the interaction region must occur. The first has temporary
stages and shields in place of the Belle-II detector. The second is the complete interaction
region installation, integrated with Belle-II, including complete supports and cryostats for
the QCSL and QCSR magnets. There were two installation scenarios presented. Bothalternatives have pros and cons and their choice will have impacts on the detailed designsof the VXD, but the decision path was not explained. However, it was stated that thisdecision needs to be made soon.
No development strategies and decision points were presented to address the technicalissues remaining with the QCS Bridge. The present design is understood andacknowledged as being weak and subject to unacceptable vibration amplification, unlessthe vibration of the QC1E and QC1P occurs with a favorable phase. It was indicated thatthe timeframe for addressing this issue was quite short, but no specific approach,development plan, or decision tree was presented.
Currently the radiation shielding in the IR region was shown to be insufficient. An
acceptable solution needs to be found and simulated. The solution may need involvementfrom others within KEKB, as the optimal solution may not be achievable with the current
boundary conditions.
The schedule and milestones were not presented at a level sufficiently detailed to allow
the review committee to assess as to the ability of KEKB to understand and address risks
before they become issues and to address issues prior to them becoming major
impediments to successful completion of construction, installation and integration.
Recommendations:
1) Continue the detailed evaluation of all sources of beam induced background to
identify and mitigate the major loss terms in the detector to prepare for shielding; thisincludes the impact of the additional weight on the QCS support system, IR vacuum
pressures and possible modifications to the walls of the experimental hall.
2) Make a decision on the baseline design for the QCS Bridge and installation. If needed
evaluate the risk and develop a mitigation strategy. Evaluate and mitigate the IR
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region schedule risks for fabrication and installation.
10)

Beam Background
Detailed studies of beam losses around SuperKEKB have been done in order tounderstand 1) the expected backgrounds in Belle-II, 2) radiation exposures to the detector
components, 3) detector channel occupancies for data triggering and analysis, and 4)
needed radiation shielding. The backgrounds come from synchrotron radiation, beam-gas
scattering, lost particles from the beam Touschek lifetime, and beam-beam radiative
Bhabha lost particles. The overall beam lifetime is about 6 minutes at the peak luminositywith each beam losing about 7 to 10 mA per second.
Synchrotron radiation has been controlled by minimizing the dipole bend angles for thebeams entering the IR. Remaining synchrotron radiation x-rays are controlled by small
masks in the vacuum chamber to avoid scattering them into the vertex chamber.
Beam-gas scattering can direct lost particles into the detector and is controlled byminimizing the vacuum pressure near the IR and around the ring. The IR vacuum group is
actively adding pumps to the vacuum chamber design to lower the expected pressure atfull currents. Scrubbing runs at high currents will reduce the vacuum pressure in the restof the ring. Collimators are being added to reduce the losses in the IR. The beam gas
lifetime is expected to be about 25 to 46 minutes.
The Touschek lifetime in the rings is determined where the beam size is smallest. The
optical quadrupole lattice has been studied to enlarge the average beam size and raise thelifetime. The Touschek lifetime is now on the order of 10 minutes in both the LER andHER at full currents.
The beam-beam radiative Bhabha scattered lifetime is about 20 to 28 minutes for the tworings. The only method to reduce this background is to collimate lost particles away fromthe IR to prevent scattered particles from traveling multiple turns and striking the detector.
The radiative Bhabha beam lifetime is about 20 to 28 minutes.
All these lost particles have been tracked in simulations with known vacuum chambers
dimensions and collimator apertures so that the locations of the losses can be determined.
These loss rates and locations have been sent to the Belle-II group to allow them to do
detector background studies. Extra shielding is being added inside the final focus
quadrupole cryostats. With these mitigation methods the detector backgrounds are
hopefully within bounds of what Belle-II needs. Further studies are underway aiming atfurther gains. Measurements of the backgrounds during early accelerator commissioning
will be done without Belle-II in place by using a suite of small detector elements called
BEAST-II.

11)

Collision Feedback (dithering)
The vertical and horizontal systems were presented in separate talks (Collision Feedback(dithering) and in Diagnostics). However, the two tasks are related and best understoodas potentially coupled controllers. Each IP feedback system computes a beam collision
impact parameter, and applies a correction signal through corrector magnets. The
disturbances in each system arise from vibrations in the final focus magnets, and thismechanical system is not going to vibrate with orthogonal motion in the two beam planes.
Each system needs to be analyzed as a closed loop dynamic system, and the disturbancerejection can be estimated at the various oscillation frequencies.
The analysis of the combined performance requires considering them as an integrated
system.
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The essential differences in the Vertical and Horizontal IP feedback systems are the useof beam-beam deflection and BPM measurements in the vertical plane, and the use of theluminosity signal in the horizontal plane. The required system bandwidths are estimatedto be very different, based on estimated oscillation frequencies of various modes of
motion in the final focus girders and magnets.
Horizontal System
The Horizontal system is estimated to require a bandwidth of 3 Hz. Examples developed
at PEP-II were used to suggest a starting plan for a horizontal dither system based onmagnetic deflection, and using a lock-in (synchronous demodulation) detection on the fast
beam luminosity signal. There was some discussion about detection at twice themodulation frequency; the choice has to do with the depth of modulation applied to thecolliding beams. As the essential goal is to increase luminosity, small modulations that
do not significantly lower the integrated luminosity, but still provide a clear error signal
are preferable. As mentioned at the review, one can detect both amplitude and phase of
the modulation to get a discriminant that has the necessary sign of the error.
We recommend doing some simple modeling of the system based on the knowledge ofthe final focus optics, and estimates of the count rates in the luminosity monitor (some ofthis formalism has been done as part of the PEP-II design and is probably useful to adapt
for the KEKB case).
As the luminosity signal is probably computed through a digital process, there really isn’t
any need to purchase or evaluate lock-in amplifiers as electronic systems – thesynchronous demodulation algorithm can run on a general purpose or specific DSP/FPGA
processor, and drive the deflection dither magnet through a digital control path. One niceaspect of a DSP-based controller is that there can be several related controllers depending
on final focus optics, operational currents and luminosity count rates, each optimized fora particular operating point.
The detailed design of the feedback controller is going to require knowledge of thefrequency response of the actuators, the bandwidth of the luminosity monitor,
signal/noise in the luminosity signal, etc. It may also be beneficial to use informationfrom the vertical system as there may be cross coupling in the mechanical vibration
motions.
The operational experience from the PEP-II implementation will be helpful to the systemdesigners.
Vertical IP feedback system (presented in the diagnostics talk)We see progress since the last review but some comments from past years are still valid.
We encourage a closed loop analysis of the complete system, including the frequency
responses of the proposed DSP filters, the planned PID controller, and the actuator
including skin effect. We are not sure what sort of closed loop bandwidths, or closed
loop frequency responses are possible with the complex CIC filters with 1 ms group delay(for example, at 1 kHz the group delay is 2*pi, so the controller will oscillate with a unity
loop gain). We stress that doing some simple control loop modeling is valuable before
building the system.
We suggest evaluating the planned PID controller andunderstanding the limits of this approach, while the FPGA based controller
implementation is flexible and may be modified later. We think it is valuable to have astarting design that works in simulation. We think this vertical error may be crosscoupled to the horizontal system, and the controller may be a multiple-input multiple

Page 12 of 28

output structure. The required bandwidth of this system may have to suppress motion at
53Hz, so that the overall system unity gain frequency may need to be nearly a kilohertz.
12)

Vacuum Construction Status and Schedule
KEKB has shown itself very aggressive and capable in addressing the challenges of themain vacuum design and production. Production of the standard vacuum components is
progressing well. A manufacturing facility has been set up for assembly, TiN coating andbaking. The HER copper racetrack chambers and the LER Oho RF cavity section havebeen completed. The rotatable SX section, beam monitor section and Fuji crossing-point
chambers are all in production. Gate valves, getters and bellows are near completion.
The design of the chambers for beam injection, abort system and the SR monitor in the
Fuji straight section will be completed soon, and production will take place in 2014.
These are all required for Phase 1 commissioning.
With regards to the dust/contamination issue discussed in the last report (“Preparation
before Installation” p.13); the vacuum group carried out an investigation and found thatthe root cause was in chamber fabrication and welding. The committee recommends
working with the vendor to reduce the contamination, as it is difficult to effectively clean
dust particles in a chamber and an alcohol wipe may compromise the bake out. In
response to the previous recommendation, the vacuum group has established a “checklist”
to track the history of all chambers.
The antechamber vacuum chambers do not have cooling at the entrance to theantechambers (the corner). During low current operation (20 mA) with interlocks off, it
is unclear whether the chambers can handle a direct SR strike at the corner radius due to amis-steered beam?
As part of the integrated vacuum system design, a few considerations should be
investigated. First, the new RF finger design in the bellows is a novel and clever solution
for high current storage machines; however, these bellows only allow for up to 4mm of
motion and some small angular motion. During the recent earthquake there was up to 10
mm of motion of the vacuum hardware. The current KEKB bellows were damaged, but
protected the more expensive vacuum hardware. The new bellows design should also
provide adequate motion to protect the main vacuum chambers from damage during alarge earthquake (20-year event?), as these are usually the quickest components to repair
and replace.
Another integrated system design issue regards the resistive wall losses and HOMs. The
vacuum group has done an excellent job to ensure that they have a low impedancemachine with inner vacuum walls made from copper, aluminum or gold. It may beadvisable to make sure that susceptible equipment, such as BPMs and strip-lines are not
the most resistive items in the system or the only place that TE modes will be absorbed.
The new RF bellows design has been tested successfully in KEKB, however, there is stillconcern that if the alignment and manufacturing tolerances between the teeth results in avery small gap at the area where the image current is high, this could potentially result inan arc. The peak electric field generated at the time of the bunch crossing should beanalyzed to ensure that it is less than the breakdown voltage in vacuum for an
infinitesimally small gap.
The committee wants to commend the vacuum group for their excellent progress.

13)

TiN Coating and Baking

Page 13 of 28

A large number of vacuum chambers in the SuperKEKB project require TiN coating on
the internal surface to mitigate electron cloud effects. 180 HER chambers require baking
and 1000 LER and 100 Damping Ring chambers require TiN coating and baking. Since
the Fall of 2012, a coating facility at the KEKB Oho Lab has been in operation with 4
baking systems and 4 coating equipment systems. There eventually will be 4 verticalcoating systems for straight chambers, with one back-up system, and 3 horizontal coating
systems for bent chambers. Processing of a vacuum chamber is time intensive. It takes 3days for baking and an additional 3 days for TiN coating. Consequently, it takes
considerable labor and calendar time to complete all of the processing. At present a 10person team is assigned for this task.
For baking, a hot-air heating method is employed, and to date most of chambers have met
the targeted pressure of 1 x 10-7 Pa. The weekly output is 10 chambers. For coating, thethickness is about 200 nm by Ti sputtering in Argon and Nitrogen gases. The weekly
output is 11.8 chambers. The KEKB team has encountered a variety of problems andgained considerable experience. Nevertheless according to the production schedulepresented in the construction project overview, the throughput remains below the targeted
levels (~75% of target). Significant increases are expected in production by the
beginning of April 2013 (a factor of ~2.4 over the present rate) and six months later (afactor ~3.1 over the present rate). These increases in production are very aggressive withcompletion of coating anticipated by the end of 2014 provided the increases in production
can be realized on schedule. This is a very tight schedule.
14)

Collimator
Collimators are necessary for fully successful operation of SuperKEKB in order toaddress beam halo and Touschek background issues. Presently the plan is to use 10 new
horizontal and 3 new vertical collimators in the LER for SuperKEKB. For initialcommissioning, only 2 horizontal collimators will be installed on the LER, while theexisting KEKB collimators will be reused in the HER. All of the collimators will be
installed and upgraded to the new Version 6 design as commissioning and operations
progress.
The Version 6 collimator has movable tungsten heads within the vacuum chambers withintegrated cooling. The length of this version of the collimator has been reduced to ~1
meter providing reducing the pressure on beam line real estate in heavily
congested/instrumented areas of the accelerator. Part of the reduction in length of thecollimators is to accommodate higher order mode (HOM) absorbers needed to help
eliminate trapped modes. Power deposition levels are estimated to be within what watercooled copper can handle.
Areas that remain to be developed include the RF connections between the vacuum beampipe, the movable collimator heads, and the HOM absorbers.
The first prototype of the Version 6 collimator should be ready for initial tests in March
2013. As previously mentioned commissioning will begin without the HOM absorbers as
it is estimated that the loss factor resulting from HOM is low. This approach as well as
the phased implementation of the new collimator geometry relieves schedule pressure
from the collimators.
Two of the technical risks for the collimators appear to be manageable and restricted tothe joining of tungsten to copper and the RF connection. Both have been implemented in
KEKB and PEP-II, but advancements could be made to improve performance. Consider
taking advantage of the CTE mismatch to enhance the joint design (you could butt the
Page 14 of 28

seal in compression). The third technical risk, the design of the HOM absorbers should
be advanced to a conceptual level and simulated. The space for the HOM absorbers islimited and could have an impact on its effectiveness. There could be a trade off between
the collimator length and the HOM absorber design. The phased implementation
approach provides adequate schedule to address these issues without compromising theoverall SuperKEKB schedule.
15)

Normal-conducting cavities for MR and DR
Main Ring NC ARES cavities:
Relocation of the ARES cavities for the SuperKEKB configuration has been completed.
The power couplers are being changed to higher beta to deliver more beam power. The
new design has been successfully tested up to 800 kW. Coupler commissioning took
about 1 month, but only about 120 Hours of this was RF processing. 14 new couplers areneeded. Baking of the couplers before testing may help to improve the conditioning time.
Coupled-bunch instabilities driven by HOM and the detuned fundamental mode should be
handled by the bunch-by-bunch feedback systems. No further configuration changes areplanned for the ARES systems.
DR NC cavities:
The new damping ring cavity prototype (cavity 0), based on the ARES accelerating cell
design, has been tested successfully. The measured Q at room temperature was 93% of
the calculated value, which is good. It was only 5% less at 200 kW (0.9 MV), which isalso good. The cavity was tested to higher voltage than needed (spec is 0.7 MV).
Conditioning took 90 hours of RF processing, finally limited by radiation (with temporary
shielding in the test area). The cavity ran stably at 800 kV, 150 kW for 8 hours. Some
trips were observed without gas bursts, possibly due to problems with the LLRF system.
Some improvements will be made to the power monitoring for cavity #1 testing. Cavity#1 is being fabricated now and will be tested in JFY12. Cavity #2 will be completed andtested in JFY13. The two cavities will be installed in JFY14. An option is being
considered to add a third cavity later if needed, but this will require cutting and remaking
the welded beam pipe connections. Cavity 1 has been RF tuned and the end plates havebeen electropolished in an attempt to reduce field emission. It might also be helpful to try
high pressure rinsing and to do final assembly in a clean room similar to the SRF cavities.
Improved video monitoring will be installed for the next test.
The prototype grooved beam pipe load has been tested separately from the cavity. Up to
400 W was absorbed with no damage to the tiles or fingers.
Recommendations:
Consider baking the power couplers before testing to shorten the conditioning time. Thiswas very helpful on PEP-II and SNS.
Proceed with testing cavity#1 as planned, preferably in a system test with all HOM loads
attached.
If field emission is still strong even after electropolishing the cavity consider trying HPRand clean room assembly for cavity#2.

16)

Superconducting cavity
Recovery of all the SRF systems after the earthquake was completed. One cavity had avacuum leak on an indium seal. The flange was re-torqued and the leak was sealed but
the cavity performance was degraded by field emission. This cavity may be a candidate
Page 15 of 28

for recovery or reprocessing. Several other cavities are strongly limited by field emission
and could benefit from improvement.
New estimates of HOM power into beam pipe loads have been made, suggesting that theexisting installed ferrite loads may be sufficient for Super KEKB. This is an importantquestion. The new calculation method based on a time domain/wakefield method shouldbe equivalent to the previous loss parameter method or frequency domain analysis. Since
the new values are lower it would be wise to cross check, and maybe benchmark the old
configuration against historical data from KEKB running. New SiC loads are being
developed for the small beam pipes between cavities and these are a good idea in any caseto absorb the high frequency HOM power that can propagate between the cavities.
Horizontal high-pressure rinsing has been tried successfully on a test cavity. Performance
was recovered from 6 MV/m to 12 MV/m on the second attempt, almost back to theoriginal level. The spare cryomodule has been similarly processed with the power
coupler removed as a precaution, then reinstalled. It will be tested in the near future. If
successful this would be a very nice way to recover the remaining modules with muchless effort than disassembly and reprocessing. If, however, the spare cryomodule is still
field emission limited after the horizontal rinsing it may be worth trying helium
processing. This has been very successful in recovering field emission limited cavities in
CEBAF.
The existing complement of cavities will be used for beam commissioning. Later, aseries of hardening measures can be implemented if needed such as higher power HOM
loads, reprocessing of cavities etc.
Recommendations:
Cross check the calculations of the HOM load power carefully, comparing time domain
and frequency domain methods and benchmarking against historical data from KEKB
running to make sure that the existing beam pipe loads are really stable in the newmachine.
Continue to develop the 150mm SiC beam pipe loads for installation between the cavities
to absorb the high-frequency HOM power.
Proceed with testing the horizontally–rinsed spare cryomodule as planned.
If field emission still persists, consider helium processing as well.
Continue to develop “hardening” strategies for the SRF systems in case they are needed
later as the luminosity is ramped up.
17)

Improvement of LLRF system
The committee notes excellent progress since last year, and we appreciate the “out of loop”
measurements of the regulated phase and amplitude. The presentation shows steady statenoise and regulation, as well as dynamic responses are interesting. If a step set-point
disturbance is applied, what is the step response of closed loop system? How are the P
and I gains set in this controller to have adequate gain and phase margins? The measured
data is presented in the time domain, is there any information in the frequency domain?
(has there been spectral information computed to look at the frequency content in thecontrol signals or error signals?) We are impressed by the work in the last year and hope
to see some of these dynamic tests of the closed loop system in the next review.
In this year’s presentation a klystron PLL concept is highlighted which would correct for
insertion phase shift vs. operating point of the high power klystron, but as shown thisPage 16 of 28

does not include the gain variation (the overall control loop gain varies as the large signal
gain of the power klystron changes due to HV power supply). This gain change will
modify the control loop gain and phase margins of the PI controllers as the ring current,
and klystron operating point vary. A similar klystron operating point loop was
implemented in the PEP-II LLRF (klystron saturation loop) and also in the LHC LLRF
(Klystron Polar loop), and the KEKB LLRF designers may want to look at theseexamples for ideas on how the closed loop margins are held constant as the klystron large
signal gain and insertion phase vary over the operating range.
The talk shows that a new design version (B version) will move interlocks from hardware
to firmware in the FPGA. While this is a flexible general-purpose approach, what
happens if the LLRF system doesn’t boot up or load the FPGA properly, or some
software process hangs up? Does this leave the expensive klystron and hardware
unprotected? Maybe interlocks should be very robust and not a software function.
The system design with the energy storage cavities, or the superconducting cavities does
reduce the impact of the high beam current on the cavity fields. However, the beamloading is not zero, and it may be useful to estimate the beam current loading in the RF
system, and estimate gap transients for possible fills with gaps or trains. This modulationof the cavity fields will drive the LLRF control loops, and it may be useful to test the RF
system controller with simulated beam signals, to see what residual disturbance is left.
Because the revolution frequency is roughly comparable to the loop bandwidth (100 kHz)the harmonics of the revolution frequency in the gap transients will not be attenuated by
the RF system. We expect these signals to be small – how do they compare to the
expected noise and resolution of the controlled system? Is the shift of the IP (thedifference between the HER and LER gap transients) acceptably small? It may be helpful
to estimate the magnitude of these effects as they interact with the LLRF cavity control
regulator performance.
18)

KEK Roadmap
The old KEK roadmap from 2008 to 2012 was discussed and most if not all the program
items were completed or started as planned. The list included the JPARC upgrade
program, enhanced KEKB/Belle program, LHC program, Photon Factory program, andgeneral accelerator and technology programs. The second item on the list is the upgradeof KEKB/Belle. This goal was very successfully launched with the construction start ofSuperKEKB and Belle II, being covered at this accelerator review.
The new KEK road map for 2013 through 2018 is in the final stages of being formulated.
It includes the strong program of JPARC upgrades including neutrinos, neutrons, protons,
and a new beam line, completion and commissioning of SuperKEKB/Belle II, LHC, a
global central ILC R&D program with an intent to host, photon science with c-ERL andthen later a 3 GeV ERL, and, finally, general accelerator and detector technology studies
with a national and health focus. This is, overall, a very strong program and matches well
the various programs around the world.
R3: The funding for SuperKEKB and Belle II including those in-house to KEK should be
carefully secured over the next few years, so that the start up, commissioning, andoperation of this state-of-the-art accelerator and detector will commence in a timely
manner.

19)

SLAC-KEK Collaboration
The committee is very encouraged by the renewed collaboration between SLAC and KEK
on Super KEKB. There is a long and fruitful history of collaboration going back to PEPPage 17 of 28

II days and beyond. SLAC has particular expertise in areas such as the positron source,
bunch-by-bunch feedback, luminosity dithering and many other areas. This collaboration
may leverage the existing US-Japan collaboration funds by bringing in other funds tosupport design and physics effort. Given the aggressive project schedule for SuperKEKB and the ongoing shortage of people on the project, this would be very welcome.
The SLAC support is subject to DOE approval but the committee is hopeful that this will
be forthcoming and strongly endorses the proposal.
20)

Overview of Injector Construction Status and Schedule
The Linac Group recovered the machine from earthquake damage by November 2012.
The group now concentrates on 4 major issues: (1) lower-emittance and high current
electron beams from an RF Gun, (2) high-current positron beams by improved capture
section and (3) lower-emittance e+ beams by a Damping Ring (DR), and (4) finally using
time sharing scheme injecting to 4+1 rings. These require improved cooling systems at
the Capture Section, DR, and switchyard.
For the high current RF gun producing 5nC/bunch, Ir5Ce is adopted as cathode material
with a high-power laser. Due to the high current, the initial energy spread of the RF gun
is large. Time manipulation of the laser is essential to reduce the energy spread during
the accelerating. The J-section is used for beam bunching. In order to improve positron
capture, they introduce a large aperture section (LAS) of S-band and 9 compact
modulators. A spoiler integrated with the flux concentrator is used to reduce the heatdensity on the FC.
After the recovery from earthquakes, the girders were redesigned, and they havecompleted alignment of a 600-m long base line of beam transport/acceleration sections.
New wire scanners and new BPMs are adopted for better beam diagnostics, and fast
LLRF is introduced for better beam controls.
The Linac Group setup prioritized work scopes with back-up options. The overall
scheme is very logical, and the committee is convinced by their near term plan.

21)

RF GunGood progress has been made on the RF guns. The DAW structure has been successfully
tested and has achieved 5 nC per pulse with a preliminary measurement of emittanceindicating ~14 mm mrad. This already meets the specification for the electron beam. The
QTWSC structure will be installed and tested soon and is hoped to give even better
performance. Two cathode materials have been investigated, LaB6 and Ir5Ce. LaB6
showed a relatively short Qe lifetime at high intensity, but Ir5Ce showed constant Qe over
45 hours running at 2.5 nC per pulse. This is a very promising result. Two laser systems
are being developed based on Nd and Yb doping respectively. The Nd system is easily
pumped with high power laser diodes, but has a fixed Gaussian profile, while the Yb
system allows for temporal pulse shaping. A Ti-sapphire based system was also
considered but had a much lower efficiency. Given the parallel approaches being pursuedin each area the committee finds it is very likely that the RF gun system will be successful.
Recommendations:
Install and test the QTWSC gun as planned.
Test the Ir5Ce cathode and Yb fiber laser system in the gun and operate for a long period
to check its reliability and performance stability.

22)

Alignment and Support

Page 18 of 28

The alignment and support aspects of SuperKEKB were presented and can be divided
into two separate areas: the rings (Magnets) and the Linac. The approach and algorithms
for the ring survey appears very mature and sophisticated involving the consideration oftunnel settling and geologic deformation including an extensive surface GPS network.
The Linac alignment and support is less mature and presently is focused on two
technologies that as of yet have not been fully reconciled: the KEK Laser PD system anda laser tracker system based on a Leica Absolute Tracker AT401.
The alignment requirements presented as being necessary for the linac for SuperKEKB
are 300 µm (rms) globally and 100 µm (rms) locally (distances ≤100 m). As reported the
KEKB linac alignment was set to be 100 µm previously, but this degree of alignment was
not maintained (nor perhaps achieved) as misalignments of the order of 1 mm and angular
misalignments of a few mrads have been documented at several locations.
The absolute laser tracker is a very strong technology approach. The published ASME
maximum permissible error (MPE) specification over a 40 m straight line is 14 µm andthe angular horizontal scale bar MPE is 361 µm at the same distance. A sufficiently
dense alignment network can improve accuracy as well.
The linac alignment is first established by component alignment at the girder level andthen using the Laser PD / laser tracker to establish girder-to-girder alignment. Geologic
or structural settling of the linac tunnel and the corresponding compromise of the survey
monuments has not been determined at this time. Final potential alignments are beam
based, but details as to the implementation were not presented. A rough plan fordeveloping a complete alignment algorithm for the linac was presented that included the
beginning of the incorporation of beam-based alignment in 2013, but with the ultimate
goal not being achieved until 2015, coincident with the start of commissioning. There
should be some effort to accelerate this to avoid the possibility of impacting
commissioning.
In the rings, it may be desirable to look for a survey/alignment solution that is nothorizontal but planar to minimize the deleterious effects of the differential structure
settling.
Sufficient detail of the support structures was not presented and so the review committee
cannot comment on the stability, ease of alignment or realignment of the structures usedin either the rings or linac.
The KEKB team may wish to explore the possibility of holding a small workshop or
review to examine the alignment and support approaches and algorithms.
23)

Positron Source
The Positron Capture Section was redesigned, replacing the L-band system by the Large
Aperture S-band (LAS) system, which will give a sufficient positron conversion rate, ashigh as 49%, and eliminate satellites. The e-beam target design was optimized to
improve the efficiency of the cooling and reduce the fields created by eddy currents. A
spoiler is integrated with the target to reduce the heat density on the target. The target
size should fit into the available space between the yoke and flux concentrator.
The first prototype of Flux Concentrator (FC) was fabricated with the help of SLAC and
IHEP. The prototype FC was built for a stand-alone test with a simplified vacuum
chamber, and was tested with a prototype modulator up to 1.36 kA. On the FC material,
OFC and HRSC will be compared in prototypes I and II. A quick detachable girder isintroduced for replacement of FC with the minimum radiation dose. The schedule forPage 19 of 28

commissioning of the 6 kA FC modulator is set in December 2013. Further improvementof the modulator with currents up to 12 kA is expected before the end of 2014. The beamtransport bypassing DR was designed for common e+/e- injection to main rings.
24)

Flux Concentrator Modulator Development
The basic requirements for the flux concentrator (FC) are the peak current of 12 kA and 5µs pulses in 50 Hz with an amplitude stability of 0.3%. The FC modulator is modified
from the KEKB klystron modulator and uses a thyratron as the switch. The parameters of
the KEKB modulator are 22.5 kV, 4.8 kA and 5.6 us pulses at 50 Hz. The prototype of
the 6 kA modulator was tested successfully. By doubling the capacity bank and coaxial
cables, the required 12 kA modulator will be assembled for tests at the end of theNovember this year. For a stable operation and easy maintenance of the modulator, KEK
developed a solid-state switch to replace the thyratron tube as a switch. The jitter ofthyratron tubes is within 10 ns and the solid-state switch should have a similar or better
performance in term of jitter and long-term reliability.
Recommendation: The discharge waveform of the modulator for the flux concentrator
with cables should be checked experimentally, to demonstrate that it meets therequirements of the optics design. On thyratron and solid-state switches, one shouldmake sure that the devices meet the jitter specification with the safety margin.

25)

Commissioning of Electron Beam
The KEK linac will start commissioning with electrons in the fall of 2013. All the beam
parameters needed to make the linac injection into the four rings successful in top-off
mode were discussed. Somewhat different parameters are needed for each of the rings:
Photon Factory PF, Accumulator Ring AR, and SuperKEKB LER and HER. The injectedbeam parameters for SuperKEKB are significantly more difficult than for KEKB withgreater charge and smaller emittances. Simulations of the beam dynamics and tuning
techniques have established the required tolerances. The larger beam charge makes thetransverse emittances and energy spread more difficult to keep small. The linac has tooperate with different bunch charges for different injection scenarios, e.g. top-off or fillfrom scratch. These various beam conditions will require different control and diagnostic
configurations.
The expected beam emittance at the end of the linac depends on the alignment tolerances.
However, some of the random seeds in the simulations produce small emittance. Thus,
studies should be carried out to determine which error seeds produce small emittances
and the mechanism involved. Perhaps, the errors cancel or are compensated, and asimilar method can be used in the real accelerator.
The next phase of planning for commissioning is to make detailed plans how each beam
parameter will be measured. Following the measurements, detailed tuning proceduresshould be developed to address the tuning issues for each parameter. Finally, a timeschedule should be made to indicate all the measurements and beam tuning that will need
to be done in sequence. Part of this time planning is to fit within the injection periods for
the PF and AR while preparing for injection into SuperKEKB.
R1: After identifying the parameters that the linac electron beam needs to meet, a detailed
set of procedures should be made for each parameter. An overall time schedule to carryout these procedures should be developed to match times needed by the four rings.

26)

New Transport Line for PF-AR
The operation of the SuperKEKB accelerator system will require continuous injection
Page 20 of 28

from the linac. At present, the linac also serves as the injection for the PF-AR ring withtwo 15-minute duration injection periods per day. SuperKEKB will not be able toaccommodate the loss of injection to rings for a period of 15 minutes at a time during
normal operations and so the PF-AR ring injection must be reconfigured to allow fastswitching of the linac electron beam and top-off injection into PF-AR. The top-off
injection is also strongly desired for better stability for PF-AR experiments. These dictate
the development of a new transfer line for the PF-AR.
This new transfer line will be housed in a new tunnel that will cross above the KEKB
tunnel. The design of the new tunnel is complete and civil construction is slated to startcoincident with the 2013 fiscal year and be completed by the end of the fiscal year. The
construction the tunnel and installation of the new transfer line should not disrupt the
KEKB. However, potential impacts of the removal of soil/shielding above the KEKB
tunnel and the installation of the new tunnel on the KEKB tunnel were not presented.
Similar disturbances at other facilities have changed the local geological behavior intunnels (settling or uprising for example) and even degraded radiation shielding. The
review committee hopes that such potential impacts have been or will be examined prior
to construction and that they present minimal risks to KEKB.
27)

The Damping Ring, Transfer Lines, and HER Abort System
The Damping Ring and transfer line civil construction has been completed since the last
review, and installation of structures, piping and other systems has made substantial
progress as well. For the damping ring, a majority of the magnets have been delivered, asubstantial fraction of the power supplies, and all of the vacuum chambers. On thetransfer lines, all of the magnets have been received as well as the large majority of thepower supplies. Progress seems on track for the completion of both the damping ring andthe transfer lines to meet the identified milestones: September 2014 – completion of the
LTR and RTL to allow unimpeded Linac commissioning; May 2015 – injection from thedamping ring into the LER.
The beam abort system (BAS) forms a critical part of the machine protection system forSuperKEKB. There are several technical and practical risks that the SuperKEKB teamhas addressed. The baseline BAS design consisted of nine principal components on boththe LER and HER:a) Horizontal kicker to deflect the beam from the ringb) Vertical kicker to spread the beam to decrease energy deposition on the extraction
windowc) Pulsed quadrupole on the LER and DC sextupole pair on the HER to increase thehorizontal size of the beam to decrease energy densityd) Lambertson Septum to bend the deflected beame) Power suppliesf) Pulse compressiong) Beam dumph) Titanium extraction window
The approach is to kick the entire stored beam out of the rings within one orbit revolution
with a rise time sufficiently fast to avoid intermediately perturbing the back of the bunchtrain once the abort is triggered. This requirement is necessary in order to avoid
damaging the machine or disrupting the RF system. The requirement of the rapid risetime results in a practical limit of one power supply for each ring. There is a need tospread the beam as much as possible in order to reduce the energy density deposition.

Page 21 of 28

The KEKB team has adopted an alternative presented previously of using two sextupole
magnets instead of pulsed magnets to enlarge the horizontal beam size at the extraction
window on the HER. Careful beam dynamics modeling were presented that included thedetermination of the dynamic aperture. These showed that the use of the two sextupole
magnets did not degrade the stored beam. The sextupole magnet specifications are notstringent and present little technical risk. The review committee agrees with thissimplification of the system since reducing the complexity will make ensuring reliability
easier.
During Phase I commissioning, only the HER abort system will be installed and theexisting LER abort system will still be in place. This will mean that duringcommissioning runs, the current in the LER must be limited to 500 mA to avoid
catastrophically damaging the existing abort window. This maximum current limit can beexceeded during beam scrubbing runs by increasing the emittance of the beam to decrease
the energy density of the aborted beam. The new LER abort system would be installed
for Phase II commissioning.
A number of open technical/engineering issues were discussed during the prior review
that were not followed up on during this review. Consequently, the review committee
cannot comment on the adequacy of implemented solutions. These issues included suchthings as the loss of the supplier for the ferrite cores necessary for the BAS, and therecommendation that the use of a striped type coating ceramic chamber or a slot typekicker be studied for generating this pulsed magnet field with a rise time less than 200ns.
28)

Beam Diagnostics
The committee is impressed by the effort and depth of the diagnostics team.
The machine diagnostics include multiple BPM systems, DCCT, bunch-by-bunch current
monitors, loss monitors, tune monitors, and several innovative photon-based beamdiagnostics. They are a mix of evolutionary designs proven in KEKB and some newideas specifically developed for SuperKEKB. The damping ring also requires diagnostics
and feedback systems.
In this review we learned about the plans to install 100 “displacement sensors” in themain rings, which we understand are capacitive systems to measure the locations of selectBPM assemblies with respect to magnet positions. We have not had any sketch or
schematic explaining if these are in the vertical plane, horizontal plane, how they are
calibrated or read out, etc. If these displacement sensors require resolution consistent
with the BPM systems, and long-term stability is important, the mechanical and electricalreview of this system may be helpful. In this review we have no detailed presentation of
their performance or operating principles
The heterodyned HER 1018 MHz and LER 509 MHz narrowband systems are fixed indesign and their performance is understood. The HER systems are from KEKB, a small
number of the new LER systems have been fabricated and performance tests arepresented. The plan is to ramp up production of these units, and the turn-by-turn gates, inthe next year.
The gated turn-by-turn systems are intended for injection studies and are based on logratio detection with external gates.
There is still some uncertainty on the technology for the medium-bandwidth processing
used for faster orbit motion studies, abort signal generation and a special longitudinal
position monitor (bunch phase monitor). Commercial processing systems have been

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evaluated and measured results of resolution are presented, but we do not see a
specification on what performance these systems must have. We think having somenecessary specification for each would help make this decision, and help finalize theplans.
If the abort signal latency is too long in the commercial system, who is going to modify
the firmware/implementation in the commercial processor? If it is someone at KEK, wecaution that the manpower to do this comes from a very busy team.
The mechanical designs and fabrication of the physical BPM buttons and vacuum
components is well underway.
Coupled-bunch Feedback
The plans are well underway and most, if not all, of the components for the transverse andlongitudinal coupled-bunch feedbacks are in progress. The KEK experience andexpertise with these systems is impressive. The damping ring will also use the samegeneral transverse feedback processing and hardware.
The transverse systems are evolutionary developments from the original KEKB systems,
but for SuperKEKB, longitudinal feedback will be installed in the LER. The longitudinal
kickers will be of the over-damped cavity (Frascati) style design.
As in past reviews we caution the beam induced power in the kicker assemblies can bedifficult to manage, and the plan is to use a mix of low-pass filters (absorptive?) andcirculators to protect the power amplifiers. Based on the PEP-II and KEKB experience,
we strongly urge care with temperature monitoring and interlocks for all the feed-throughand high-power cable assemblies on the beam line. We complement the team for having
planned for spares on the high-power amplifiers at this early stage.
The original KEK bunch-by-bunch beam orbit detector is available to implement tune
monitors and provide diagnostics for the feedback systems.
Vertical IP feedback
Considerable design and measurement information is presented on the signal processing
for the vertical IP orbit feedback systems. In the last year considerable technical progresshas been made on improving the system resolution to the 0.1 micron level, and a feedback
controller processor is in development (based on the LLRF micro-TCA hardware).
However, we feel strongly that this sub-system of the IP feedback needs to be developed
as a part of an integrated feedback model, which allows the closed-loop performance of
the IP feedback to be estimated. We are concerned that this beam detector function is
being developed as a stand-alone BPM function without consideration of the technicalimpact it has inside the overall IP feedback loops.
The original DCCT is being refurbished for SuperKEKB, and it is planned to re-use theLoss Monitor system. In the next year the resolution of the system will be evaluated and,if necessary, a new readout system will be designed. Again, manpower to do thisevaluation and design is in competition for many other tasks, and the team may want toprioritize the importance of the loss monitor in the initial stages of commissioning
without the Belle detector.
Plans for the damping ring BPM and feedback systems have been presented mostly inschedule timelines, without specific requirements or technical specifications.
Photon Diagnostics

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Three types of photon monitor are envisaged for the SuperKEKB, described in somedetail in the previous Review. The Synchrotron Radiation Monitor (SRM) will use a
streak camera for the bunch length and an interferometer for the horizontal beam size
measurement. It can also be used for the vertical beam size measurement in the earlystage of the commissioning, however the design vertical beam size cannot be resolved.
The X-ray monitor (XRM) for the small vertical beam size will use the coded-aperturetechnique. The experience with XRM gained at CESR-TA beam is of vital importance forspeeding-up the development of SuperKEKB XRM.
Finally, the Large-Angle Beamstrahlung Monitor (LABM) will be used for the collision
tuning. Its experimental test is being prepared. For the exceptionally small vertical beam
sizes in the SuperKEKB IP, a coherent regime of beamstrahlung should be considered, its
potential applicability to the beam-beam collision offsets monitoring should be evaluated.
The committee is satisfied that the development of photon monitors of all three types
shows good progress since the last Review. The construction plan for the visible lightand X-ray beam lines, optical and electronic component in both DR and Main Rings is inagreement with the current commissioning scenarios.
Construction Plan
The timeline for the next three years shows many design and evaluation projects inparallel, as well as many production projects in parallel. We are concerned about
available technical resources to do so much in parallel. The testing and installation of
hundreds of cable assemblies, BPMs, complex electronic systems, etc. is going to be amajor task and critical to manage with the limited human resources.
Recommendation
The dynamics of the IP feedback loops should be studied using a method that captures thefrequency responses of the critical elements including the beam dynamics, the magnet
motion dynamics, the responses of the BPM system, and the controller and the correction
magnet/power supply/eddy current effects. Ultimately this model should be coupled andintegrated into horizontal IP feedback model, as we would expect there would be crosscoupling in the system dynamics.
29)

Estimation of Beam Loss
A comprehensive simulation of the beam loss distribution around the main rings is donein order to provide correct input for the detector background estimation, for the radiation
protection design, and for development of beam loss monitor system. Beam-gas
Coulomb scattering, radiative Bhabha and Touschek loss are studied. The total LER loss
rate per bunch of 1 mA amounts to about 107 pps and about 5 times less in HER.
Touschek loss is dominant in the both rings. Physical rather than dynamic apertures wereapplied in the particle loss condition. Tracking included only one to ten turns.
The Committee recommends multi-turn tracking of particles to be lost, so that the
dynamic aperture limitation would be a cause of their loss, because the resulting loss
distribution around the ring may significantly differ from that obtained in a few-turnsimulation.

30)

Control
The overall control approach is a mature system, based on EPICS. We endorse the plan
to re-use as much as practical from the existing controls infrastructure given manpower
limitations.
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The committee enquired about the issues in maintaining CPU and software systems in theIOCs over long lifetimes of the project, as commercial product lifetimes often are a few
years. We understand the group plans on buying spares as part of the development of the
new system. We endorse this approach, and recommend that even with tight budgets
there be designation of spares for critical IOC CPU and module functions.
We also encourage the controls effort to collaborate with other laboratories on security
and network protection through the ICALEPS and other mechanisms, as lab facilities are
attractive targets for external attacks and malicious people. The reconfiguration of thegeneral networks at KEK to minimize the connections across firewalls between external
and machine specific control networks seems a smart move towards more secure
operations.
This year there was not much discussion of the timing system, we assume it is on track todeliver the necessary RF distribution and timing/synchronization signals for KEKB. We
encourage efforts to include diagnostics into the distributions system as part of the initialdesign.
31)

Ring Commissioning
The two rings of SuperKEKB will be difficult to commission due to high beam currents
and low emittances, as discussed by the presenter. The beam and interaction region
parameters will be the most demanding of any collider operated so far. The QCS on theright side of the interaction point will be delayed by its production schedule triggering a
scenario where a relaxed IP must be commissioning for about the first year. The
parameters that are needed were presented for each scenario of the combined SuperKEKB
and Belle II plan. A phased approach to ring commissioning was adopted in three parts.
Ring Commissioning Plan I included the standard relatively simple activities of storing abeam, correcting the orbit and beta functions and getting the diagnostics to work. Ring
Commissioning Plan II was mainly beam scrubbing where extended beam storage time isused to scrub the vacuum chamber surface with beam x-rays to improve the vacuum level.
Finally Ring Commissioning Plan III is used to perform detailed lattice and beamcorrections, where extended beam time is needed to fix all the subtle first and second
order optics and IR related parameters. This proposed commissioning plan was overallquite detailed and was a natural extension of the actual plan extensively developed for thehighly successful KEKB.
R1: At some point in the commissioning plan, large beam currents will need to be stored
in both storage rings. This leads to a large AC wall plug power usage. The availability of
AC power from the local power companies may be limited due to nation wide external
issues. A long-range high power agreement may be worth negotiating for operation of
the rings in later years.

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Appendix A
KEKB Accelerator Review Committee Members
Andrew Hutton, ChairJLab

John Fox

SLAC

Stuart Henderson

FNAL (unable to attend)

Miguel Jimenez

CERN (unable to attend)

Nadine Kurita

SLAC (replacing Miguel Jimenez)

Gwo-Huei Luo

NSRRC

Won Namkung

POSTECH

Evgeny Perevedentsev

BINP

Bob Rimmer

JLab

Kem Robinson

LBNL

John Seeman

SLAC

Zhao Zhentang

SINAP

Frank Zimmermann

CERN (unable to attend

Katsunobu Oide

KEK, Ex Officio Member

Kazunori Akai

KEK, Secretary, Accelerator

Kazuro Furukawa

KEK, Secretary, Accelerator

Haruyo Koiso

KEK, Secretary, Accelerator

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Appendix B Agenda of the 18th KEKB Accelerator Review Committee
March 4 (Monday)
08:30 - 09:00 Executive Session
09:00 - 09:30 Overview of Ring Construction Status and Schedule
09:30 - 10:00 Belle II Construction and Schedule
10:20 - 10:50 Beam Dynamics Issues in SuperKEKB
10:50 - 11:20 Optics Issues
11:20 - 11:35 Magnet Overview
11:35 - 11:45 Magnet fabrication and field measurement
11:45 - 12:00 Magnet Power Supplies
13:15 - 14:10 IR Magnet
14:10 - 14:40 Construction of the Interaction Region
14:40 - 15:10

Beam Background

15:30 - 15:50
15:50 - 16:05
16:05 - 16:25
16:05 - 16:25
16:45 - 17:05
17:05 - 17:20
17:20 - 17:35

Collision Feedback (dithering)
Vacuum Construction Status and Schedule
TiN Coating and Baking
Collimator
Normal-conducting cavities for MR and DR
Superconducting cavity
Improvement of LLRF system

March 5 (Tuesday)
09:00 - 09:30 KEK Roadmap
09:30 - 09:45 SLAC-KEK Collaboration
09:45 - 10:00 Overview of Injector Construction Status and Schedule
10:00 - 10:30 RF Gun
10:50 - 11:10 Alignment and Support
11:10 - 11:40 Positron Source
11:40 - 11:50 Flux Concentrator Modulator Development
11:50 - 12:20 Commissioning of Electron Beam
13:30 - 13:50 New Transport Line for PF-AR
13:50 - 14:10 HER abort system
14:10 - 14:55 Beam Diagnositics
14:55 - 15:05 Estimation of Beam Loss
15:25 - 15:55 Control
15:55 - 16:25 Ring Commissioning
March 6 (Wednesday)

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K. Akai
Y. Sakai
Demin Zhou
H. Sugimoto
M. Masuzawa

K. Egawa
T. OkiN. Ohuchi
K.
Kanazawa
H.
Nakayama
M. Masuzawa

Y. Suetsugu
K. Shibata
T. Ishibashi
T. AbeY. Morita
T.
Kobayashi
Y. Okada
U. Wienands

K.Furukawa
M. Yoshida
T. HigoT. Kamitani
M. Akemoto
M. Satoh
H. Takaki
N. IidaH. Ikeda
T. Nakamura
Y.
Funakoshi

08:30 - 12:00
14:00 - 15:00

Executive Session / Report Writing
Close-out

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