The Fifteenth KEKB Accelerator Review Committee Report
March 8, 2010
Introduction
The Fifteenth KEKB Accelerator Review Committee meeting was held on February 15-17,
2010. Appendix A shows the present membership of the Committee. Trevor Linnecar,
Flemming Pedersen, and Wang Shuhong were regrettably unable to attend this meeting. In
addition, Mike Billing, from Cornell, replaced Dave Rice who was unable to attend.
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 forthe meeting is shown in Appendix B.
The Committee was as always impressed by the high standard of the talks, both the technicalcontent and the presentations themselves. This year however, the quantity of work that waspresented was outstanding as the KEKB group had, in a single year, taken an idea for a NanoBeam version of SuperKEKB and brought a specific design to a really advanced state. The
recommendations of the Committee were presented to the KEKB staff members before theclose of the meeting. The Committee wrote a draft report during the meeting that was thenimproved and finalized by e-mail among the Committee members.
Contents
A) Executive SummaryB) RecommendationsC) Findings and Comments
1)
KEK Roadmap
2)
KEKB Status
3)
Belle & Belle-II
4)
Simultaneous Injection
5)
Operation Experience of Crab Cavity
6)
Nano-Beam Scheme for SuperKEKB
7)
Machine Parameters
8)
Beam-beam Simulation
9)
Systematic Study of Nonlinear Dynamics
10) Fringe Field of Solenoid
11) Lattice Design12) IR Overview
13) IR Magnets
14) IR Vacuum Chamber and Assembly15) Machine-Detector Interface16) Vibration Measurement17) Injector Upgrade Overview & Positron Source18) RF Gun
19) Damping Ring
20) Beam Transport, Injection, Extraction from DR21) RF Overview
22) ARES Cavity23) Superconducting Cavity
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24)
25)
26)
27)
28)
29)
30)
31)
32)

RF Accelerating Structure for DR
VacuumMagnets
Beam Diagnostics
Impedance Estimation
Beam Abort System
Control
Facility and Infrastructure
Schedule / Budget / Human Resources

A) Executive Summary
The performance of KEKB improved considerably over the last year as new skew sextupoles
were installed and used to optimize the beam-beam collisions. The peak luminosity that has
been achieved with crab crossing is now 2.11 x 1034 cm-2s-1, significantly more than theprevious record without the crab cavity (1.76 x 1034 cm-2s-1).
The Belle detector has reached its goal of accumulating a total integrated luminosity of 1 ab-1.
This is an extremely important achievement as this was the target that had been defined for
the KEKB project. The Committee congratulates the KEKB and Belle groups for thiswonderful achievement. The detector accumulated 105.4 fb-1 in 2009, compared to 98.2 fb-1
in 2008, 86 fb-1 in 2007 and 145.4 fb-1 in 2006. The Belle detector has published, or submitted
for publication, a total of 324 papers in refereed journals (294 as of the last meeting). This
year the main focus of the physics program has been on Υ(1S), Υ(2S), Υ(3S), and Υ(5S)
running. The focus is now shifting to process aggressively all of the data and to test the
prototype components for Belle II, the new detector for SuperKEKB.
A major focus of the Review was the SuperKEKB Upgrade. Last year, the Accelerator
Review Committee had recommended “the machine design work concentrate on the low
emittance option for the next few months, with a focus on identifying any possible
showstoppers.” The KEKB group followed this advice and has made great strides in thedesign of a low emittance option (Nano-Beam), to the point where it is now considered to be
the baseline design. So far, no showstoppers were identified by the KEKB group, and theCommittee agreed with this assessment.
The Nano-Beam option also addresses a major concern – the cost of the facility. The new
design reduces the construction cost from around $560M to $390M ($1=90 yen), a significant
cost saving. In addition, the operating costs are expected to be lower, addressing anotherconcern of the funding agency.
A great deal of component R&D was carried out over the last few years and most of thisR&D was applicable to both designs. However, the focus over the last year has been the
Nano-Beam option, trying to identify any possible showstoppers. This work has provided thedetailed underpinning of the Nano-Beam design and has permitted the KEKB group to adopt
the Nano-Beam design as the preferred option.
The Committee unanimously supported the decision to make the Nano-Beam option thebaseline. Having said that, the Committee recognizes that a considerable amount of work is
still required to complete a consistent design, and recommends establishing a parameter teamto ensure that all of the systems are compatible.

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B) Recommendations
The Committee has made recommendations throughout the different sections below.
Highlights of these recommendations are summarized here.
KEKB
1) The Committee recommends preparing a prioritized program of machine and detector
studies for the final KEKB run.
SuperKEKB
2) The KEKB Group should create a parameter team to develop and approve a consistentparameter set for SuperKEKB. The team should have participation from each group to
ensure a fully integrated design for the machine.
3) The KEKB and Belle Groups should formally create a joint working group to optimize
the interaction region and the machine-detector interface. The first topic to be decided is
the rotation of the Belle detector. The second topic to be studied is how to understandand minimize the detector background.
4) KEK management should ensure that the resources needed for the Nano-Beam studies are
made available (staffing, computing). The most important issue is the establishedshortfall in staff during the construction period (~30 people) and in the operating era. In
this context, the Committee recommends exploring collaborations with universities,
industry and other laboratories world-wide.
5) The change to the Nano-Beam design has strongly increased the work in the magnet andpower supply area. This is an area where staffing is a major issue which needs to beresolved, perhaps by industrial partnerships. The Committee recommends that the
number of different magnet designs be minimized.
6) Since the vertical beam size is so small in the Nano-Beam design, all of the transverse
instabilities should be fully evaluated and mitigation strategies developed. In addition, asolution should be developed for damping vibrations of the interaction region components
and/or the beam to maintain luminosity.
7) The continued use of the older analog RF low level controls on the existing stations
should be evaluated for compatibility with the new digital systems, which are currently
only proposed for the new stations.

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C) Findings and Comments
1) KEK Roadmap and SuperKEKB Upgrade
Professor Suzuki presented the road map for the KEK Laboratory, which consists of a multipronged approach to accelerator-based science. J-PARC will soon become a world leader inlong baseline neutrino studies, and has already initiated materials science studies using
neutrons and muons. The upgrade of KEKB using the low emittance option will study CP
asymmetry and new sources of flavor mixing in the quark sector. The physics fromSuperKEKB will be complementary to that which can be obtained from LHC. KEK is
involved in LHC physics experiments and is designing the crab cavities and thesuperconducting insertion quadrupoles needed for the LHC Upgrade. SuperKEKB will playa large role in these preparations, both in the physics aspects and developing the technologies.
KEK will remain involved in preparing for energy frontier experiments at ILC and is playing
an extremely active role in the ILC R&D, both in the S1 and S2 superconducting module
program and the low-emittance frontier with the ATF. KEK will also remain in the forefrontof photon physics with the Photon Factory and later a cERL. There is also an idea for using
KEKB as a photon source (KEK-X) that would have extremely interesting photon energy
reach.
2010 is a decisive year for KEK as many projects are vying for an upgrade: the power
upgrade of J-PARC; the upgrade of KEKB to SuperKEKB; beginning the cERL project;continued involvement in ILC during the Technical Design Phase; and finally the
involvement in the ILC program. This is an extremely heavy load and at some stage it will
be necessary to prioritize. The outlook for SuperKEKB is extremely positive, withconstruction expected to start in JFY2011 with a four-year construction time. The total
construction cost envisioned by the funding agency is $300-400M and the operating costshould not significantly exceed the present annual operating budget of $60M.
2) KEKB Status
One year ago, the luminosity with the crab cavities was still less than had been obtained
without the crab cavities, and no remedy for this had been found. In the last year, the ideathat the limitation was due to chromatic errors in the coupling compensation was developed.
A set of compensating skew sextupoles was built, installed and commissioned, resulting in asignificant step forward in luminosity (15%). The KEKB group is to be congratulated on
finding the cause of the luminosity limitation and the resulting world record for luminosity of
2.1 x 1034 cm-2s-1. This is significantly larger than the maximum luminosity obtained
without crab cavities, finally realizing the gain expected from this system. Since the tune-up
time available for optimizing the new knobs has been somewhat limited, more luminosity
may still be possible.
A major milestone was reached in November when the total integrated luminosity finallyreached 1 ab-1, the KEKB operational goal established when the project was initially funded.
This is a wonderful achievement and the Committee congratulates the KEKB and Belle teams
who have worked so hard for so long to achieve it.
A factor in increasing the integrated luminosity was the achievement of simultaneous
injection into the LER, HER and Photon Factory. This required a complex set-up with a fast
event generator and is a significant step forward in preparing for SuperKEKB.

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Machine development has been devoted to evaluating hardware for SuperKEKB as well as
demonstrating new techniques. Since there is only one more short operations run planned
before dismantling KEKB and preparing for SuperKEKB, the time needs to be planned
wisely. The Committee recommends preparing a prioritized list of machine activities for the
final run.
3) Belle & Belle-II
The Belle detector worked well during the last run and activities are now focusing on a grand
reprocessing of all of the data. In addition, new readout electronics that will be needed forthe expected faster data rate of SuperKEKB are being tested in the detector. This is anextremely positive development that should be continued. The required development timeneeded by the Belle detector should be folded into the prioritized list of activities during thefinal run.
A brief outline of the physics case for SuperKEKB was presented. The Committee
recommends that this case be strengthened and, more importantly, made crisper. In the
coming year, it will be necessary to convince politicians and government officials of theimportance of building SuperKEKB, so the arguments need to be aimed at non-experts.
4) Simultaneous Injection
The Committee would like to extend their congratulations to the injector group for the
success of simultaneous injections of different beams to three rings in 50 Hz top-up mode (20ms). It has taken many years of thorough planning and careful step-by-step execution. First,
the dual-bunch positron injection in 2003 and top-up injection in 2005 improved theefficiency of filling the KEKB rings. Starting with the by-pass transfer line to the Photon
Factory, about 1000 devices were improved or modified. In addition, beam diagnostics, a fast
control scheme and the fast event system with pulse-to-pulse reprogramming, have been
implemented. Finally, the group achieved the remarkable milestone of completing the“Event-based Control System” in April 2009. It will be essential for the Super-KEKB
operations due to the expected short beam lifetime. Again, they have done a remarkable jobvery well.
5) Operation Experience of Crab Cavity
A detailed account of the operational performance of the crab cavities since their installationin KEKB in 2007 was presented. The cavities have been essential to achieving the world
record luminosity in KEKB. In spite of their complex and delicate design, the operation has
been remarkably stable, with an acceptable overall performance over the years. Most recently
the cavities have been operated with beam currents of 1250 mA in the HER and 1700 mA
and in the LER. The trip rates have been improving with time, coming down to values ofabout 0.1/day for the LER and about 0.8/day for the HER.
The design parameters were shown to remind the Committee of the many critical components
in the crab cavities. The HOM load dampers have operated reliably beyond their design
power levels. The sudden breakdown of the piezo-actuator has not stopped the operation of
the LER since the low level feedback can compensate for this failure. Unfortunately, thereduction of the maximum cavity voltage after installation in the LER, as reported to aprevious MAC, has never been recovered. Lowering the operating temperature and RF
conditioning have been without success, and this problem remains a subject of concern. Morerecently an oscillation at high beam currents has (again) been observed for unknown reasons.

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The Committee congratulates the KEKB team for the important contribution it has made withthe crab cavities to accelerator science and technology. As the crab cavities are no longer
needed in the Nano-Beam scheme, it is satisfying to hear that they will be used in the future
for machine studies at CERN in the context of the LHC luminosity upgrade.
6) Nano-Beam Scheme for SuperKEKB
The KEKB staff has performed a careful investigation over the past year comparing the High
Current option for SuperKEKB as well as the Nano-Beam scheme. Many accelerator physics
and engineering topics were covered. Many of these topics were needed for both schemes.
After looking at overall issues such as minimizing operating costs, minimizing construction
costs, optimizing accelerator physics issues like CSR with the bunch length in both rings, andreducing the needed beam-beam tune shift for full luminosity, the team has now convergedon the Nano-Beam scheme for the construction of SuperKEKB.
The Coherent Synchrotron Radiation (CSR) effects are much less important with 6 mm longbunches compared to 3 mm long bunches. The needed beam-beam tune shifts have been
reduced from 0.3 to 0.09. The machine parameter optimization is ongoing and will likely
stabilize over the next few months as studies continue. Many engineering tests of the newcomponents have been successfully completed over the past year.
There are several key issues to resolve influencing the overall design. 1) The accelerator staff
should confer with the high energy physicists from Belle as to whether longitudinal electron
polarization is needed at the interaction region. 2) The accelerator staff should come to a final
conclusion with the detector collaboration concerning the energy operating ranges ofSuperKEKB, e.g. should SuperKEKB be capable of running at a much lower energies, e.g.
the tau-charm threshold, or whether extensive scanning of the Upsilon resonances will beneeded. 3) Rotating the detector on its support would help the optical and mechanical designof the accelerator. The pros and cons of this rotation should be discussed with thecollaboration and an optimized solution found.
Several injection issues should be resolved. A phase space plot of the stored and injectedbeams at the injection septum needs to be made to ensure all the injection parameters arechosen adequately. An accounting of the injection rates, charge per pulse, and the injectedbeam emittance should be tabularized in a systematic fashion for the Nano-Beam scheme
including requirements for the low emittance gun and damping ring.
Finally, the overall interaction region design is still in flux and additional concentrated work
is needed to converge on the optimal accelerator physics parameters there.
7) Machine Parameters
The Nano-Beam scheme for the SuperKEKB collider will be a challenge from theperspective of beam parameters. There are many new and innovative concepts that need to bebrought to fruition. The target luminosity for the Nano-Beam scheme is 8 x 1035 cm-2s-1 withbeam energies of 4 and 7 GeV. The energy asymmetry has recently been lowered to reduce
the synchrotron radiation power of the high-energy ring and to make the beam currents moreequal.
The beam currents in the Nano-Beam scheme are significantly lower than in the HighCurrent scheme, but still are a factor of two larger than for KEKB. This increase in current isPage 6 of 27

being addressed in detail, as many improvements to the RF system, ring impedances, vacuum
duct design, and feedback systems are needed.
The bunch spacing will be two buckets in SuperKEKB requiring an upgrade in bandwidth of
the bunch-by-bunch feedback systems.
The low horizontal emittances and, especially, the very low vertical emittances, will be achallenge to commission, tune, and maintain during collisions. Specialized tuning techniques
need to be developed and correction schemes optimized.
The beams are very small at the interaction point. Collision feedbacks and correlated beam
readout diagnostics need to be designed to complete this crucial operational function.
The quadrupole lattices for the rings were shown and large steps have been taken toward
completion. Many aspects have been studied. Work is ongoing to optimize the dynamic
aperture and the IR parameters. One of the next phases is to determine the allowed magnet
field tolerances, component alignment tolerances, and power supply specifications. Thesestudies include the requirement to tune the machine after construction during commissioning.
There is a plan to run KEKB in May and June of 2010 to provide Belle with more selectedparticle physics data and to do crucial accelerator physics experiments aimed at SuperKEKB.
The committee recommends that a detailed plan for the time usage of the KEKB accelerator
run in May and June 2010 be made soon so that all the essential studies get done during thiscrucial time period.
8) Beam-beam Simulation
Dependence on beam-beam simulation will increase with time. Beam-beam simulation is a
critical effort for SuperKEKB. One early result so far predicts that one must insist on thehourglass condition that beta > sigmax/2 phi. Simulation shows that the luminosity decreases
sharply when the value of beta/(sigmax/2 phi) exceeds 1. Another important prediction of thesimulation is that the crab waist does improve luminosity, but only by about 20%.
These beam-beam simulations, particularly for the Nano-Beam scheme, require a large
amount of computing power. It is suggested that KEK management addresses the issue ofcomputing power as soon as possible, given the expectation that these simulations will
become increasingly more important for the design effort.
Further studies are required to address the following aspects, among other things:
•
•
•

•
•

Confirm the feasibility of injection while colliding.
Benchmark against DAFNE.
The tolerance on the y-z tilt of the beam due to optics or the y-z banana effect due towake fields. The intentionally long bunches in the Nano-Beam scheme will tend to
make this worse.
The operation of the beam collision feedback system at the IP will require input frombeam-beam simulation.
Beam-beam collisions occur only among a small number of particles. Statisticalfluctuations will be large, causing beam-beam diffusion. This effect may needanalysis and simulation efforts.

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9) Systematic Study of Nonlinear Dynamics
In order to achieve the design parameters for the SuperKEKB collisions, a sophisticated IR
lattice is needed. The present LER IR lattice solution provides for needed small beta-y* andLocal Lattice Correction at the expense of a large beta-beat along the IR: there are 3 maxima
of beta-y ~ 2.5 km on either side of the IP.
The study of nonlinear effects in the LER included simulation of the nonlinear dynamics up
to 4th order using a Budker INP code, with the aim of enhancing the dynamic aperture.
The included nonlinearities were: strong chromatic sextupoles of Local Lattice Correction,
chromatic sextupoles of the arc, quadrupole fringe fields, bending magnet fringes (to 3rdorder) and the kinematic terms.
Although the sextupoles of both types are arranged in pairs with a –I transformation in
between, the compensation problem arises from the finite sextupole length, which leads tonon-cancellation of the nonlinear terms; the residuals start from the 4th order. But in thislattice the quadrupole fringe terms are actually dominant (by a factor of ~5) over the former.
The kinematic term is dominated by the IP section with beta-y* = 0.27 mm.
Before optimization, the vertical dynamic aperture limitation was primarily caused by thequadrupole fringe field nonlinearity (mainly coming from the final focus); the 4th orderresiduals from the sextupole pairs were the second most important. Actually two terms affectthe result: the 4th order vertical nonlinearity limits the vertical dynamic aperture while thehorizontal dynamic aperture was limited by the 4th order nonlinear coupling to the verticaldegree of freedom. Adding the quadrupole fringe field did not seriously reduce dynamic
aperture sizes because they added a positive amplitude-dependent tuneshift to reduce thenegative amplitude-dependent tuneshift from the sextupoles and thus moving the tune off thehalf-integer resonance. As for the kinematic term, its influence on the dynamic aperture wassmall.
The compensation of the quadrupole fringe terms was done by placing octupole correctors ateither end of the quadrupole (local compensation) and finding their strengths so as to(approximately) compensate both vertical nonlinearity and nonlinear coupling terms.
Depending on the position in the lattice, a single compensation octupole or an octupole
combined with the quadrupole over the entire length could do the job (needed K3 ~ K1**2).
Computation of vertical amplitude-dependent tuneshift and nonlinear coupling amplitudedependent tuneshift provided a fast and accurate indication of the compensation. The
compensation proceeded for each of the strongly contributing quadrupoles; the resulting
widening of dynamic aperture is: >10-fold in y, >3-fold in x. Actually, at this stage it was
important to demonstrate the principle and capability of the technique.
For compensating the residuals from a sextupole pair, the trick is to add two more weak
sextupoles with the same sense as in the above procedure and to find optimal strengths using
the same indication as for the quadrupole fringes. This work for the LER IR lattice is now inprogress.
The next steps are the joint optimization of the on-momentum and off-momentum dynamic
aperture, i.e. widening the momentum acceptance, the global optimization of the entire
machine lattice and compensating all known errors for a lattice. Except for the last item, thispath has been taken for the Frascati-SLAC design for SuperB lattice.
The Committee recommends further use of the compensation techniques to optimize theSuperKEKB lattice and suggests development of pre-computed recipes for experimental
optimization of the dynamic aperture and momentum acceptance.

Page 8 of 2710) Fringe Field of Solenoid
The large Piwinski angle adopted in the Nano-Beam option of the SuperKEKB collider leads
to an unusually large tilt of both beam orbits by ±41.5 mrad with respect to the Belle solenoid
axis. In combination with a very small vertical emittance, this necessitates an extension of
conventional accelerator physics approaches to reveal the effects that were believed to be
negligible in previous machines, e.g. more accurate orbit position evaluation, nonlinear
transverse dynamics and quantum excitation in the solenoid fringe field.
With a trapezoid model of the solenoid fringe field, the 4th-order nonlinear canonicaltransformation of the transverse dynamical variables has been derived to the 1st order in thesolenoid field strength, and implemented in SAD. Estimation of its effect on the dynamical
aperture is now in progress.
Next, the quantum excitation of the vertical emittance has been evaluated in the solenoid
fringe field by the relevant modifications to the SAD code. The new contribution turned out
to be so important that the rotation of the IR with respect to the Belle solenoid axis has been
re-optimized, resulting in the presently adopted ±41.5 mrad beam entrance angles. As a byproduct of this activity, a corrected calculation by SAD of the beam orbit accounting for theradiation effects resulted in a revision of the wiggler section lattice. Remarkably, the newfeatures when applied to the present KEKB optics appeared to be unimportant, but they are
critical for the SuperKEKB parameters!
The Committee recommends further improvements/revisions of the particle dynamics
calculation techniques critical for the Nano-Beam, e.g. as follows: 1) Find the acceptable
amplitude of the vertical orbit bumps which are essential in the coupling/vertical dispersion
correction. 2) Check if the vertical bends in the IR Local Lattice Correction are compatible
with tolerable vertical emittance excitation. 3) Implement in SAD the direct quantum
excitation of the vertical motion that may appear to be non-negligible in the lattice sections
with very large beta-y, etc.
11) Lattice Design
The SuperKEKB design has shifted from a high current scheme to a Nano-Beam scheme.
This is a good shift in the sense that the design burden is now more evenly shared among alldesign considerations, and the design as a whole becomes more optimized in terms oftechnical challenges. In particular, the Committee wishes to support the design strategy tosave crab waist as a further upgrade possibility and not as an essential part of the design thatis required already on Day 1. It also welcomes the fact that with a Nano-Beam scheme, therequirement of operating extremely close to a ½ integer tune is much more relaxed. The
Committee considers Nano-Beam to be a more robust scheme than the high current option.
An impressive amount of work on lattice design addressing the Nano-Beam scheme was donein the short time since the last review. The SuperKEKB team has demonstrated a solid
ability to deal with a demanding list of difficult lattice design issues.
For the Nano-Beam scheme, a significant part of the burden of proof is shifted to the efforts
for lattice design and dynamic aperture. Knowing the long list of difficult issues facing thelattice design ahead, it is suggested that every effort be made to make the lattice design
requirements as simple as possible.

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Although much progress has been made in a short time, the lattice issues remain extremely
demanding for the Nano-Beam scheme. For example, more work will be needed on thefollowing issues:
•
•
•
•
•
•
•
•
•

Further optimization of chromaticity correction, optimization of the local chromatic
sections, and ways to control chromatic coupling effects.
What is the optimal choice of magnet apertures? Can they be smaller for the
nanobeams? This is a major cost issue.
Tolerances on field errors and alignments particular to the small x-y coupling.
IR optics (small beta*, large beta_max, correction scheme, solenoid orientation angle,
tapered solenoids).
Crab waist implementation (although not necessarily on day 1; the option must be
kept in lattice design).
Momentum aperture (optimize for Touschek lifetime).
Dynamic aperture (required for injection).
Energy variation (how do solenoids and permanent magnets vary when beam energy
is varied?).
Polarized beams? (Make sure this is NOT needed. Otherwise, this will drive thedesign in a strong way, so it has to be determined early – cannot retrofit.)

Collision feedback system for vibration effects has to be integrated into lattice design.
The workload is extremely heavy. Much more work on lattice design will be needed.
In passing, the Committee wishes to comment again on the very small vertical emittance thatis the key to the Nano-Beam scheme. When the vertical emittance is small, some effects thatare usually negligible will require renewed attention. A few examples come to mind:••••

Radiation at solenoids and wigglers and other fringe fields (thanks to Oide’s work).
Vertical beam orbit alignment and jitter, and collision feedback system.
Quantum noise due to opening angle of synchrotron radiation (a small effect if it
contributes < 1 micron to vertical beam size in the arcs, but this should be checked).
Banana beam tilt in y-z plane (steady state distortion) due to lattice optics and/ortransverse wake fields.

There could be more effects to be added to this list. The Committee encourages theSuperKEKB team to stay alert to other such effects.
12) IR Overview
A schematic overview of the design for the interaction region (IR) was shown including thedetector, vacuum chambers, superconducting magnets, permanent magnets, and supports. The
design is converging but there are many topics to refine. The designs of the superconducting
quadrupoles (5) and permanent magnet quadrupoles (3) are maturing, but further evaluationis ongoing. A prototype of the permanent magnets is proceeding.
Leakage fields from the superconducting quadrupole into the aperture of the opposing beamchamber needs additional study, as the fields are not pure multi-poles and they change withposition along the beam line. Compensation with normal windings on the opposite vacuum
chamber will not be an easy task.

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The chromaticity correction of the IR quadrupoles is a crucial need for the overall dynamic
aperture of both rings. Work at the KEK and BINP laboratories is going on to find the
optimal correction. This work should be supported and carried out in a timely manner.
The accelerator design would gain significantly from the rotation of the Belle detector about avertical axis of a few tens of mrad. The difficulty for the detector collaboration to carry out
this rotation should be investigated.
As was recently addressed by original research in the KEKB accelerator group, the antisolenoids to compensate the detector solenoid need to have a soft field transition along thebeam path to minimize vertical emittance growth of the beams due to non-linear terms in thetransport matrix. Thus, the overall solenoid compensation scheme needs to be revisited.
The number and location of the diagnostics in the IR need further work to determine the best
location and needed capabilities.
The overall design needs a completed specification of the beam aperture for magnets andbeam duct design. The required studies should include the closed orbit distortions, the beamstay-clear required for adequate lifetime, the injected beam clearances, and lost particle issues
for detector backgrounds.
Keeping the small beams in collision will be difficult especially in the vertical plane.
Algorithms and the hardware to provide feedback need to be designed and analyzed.
Finally, the beams are very sensitive to the vibration of the IR quadrupoles, as the beta
functions there are by far the largest in the rings. Recent measurements of the existingvibrations of the components and tunnel in their region were done and clearly showed theneed to mitigate this effect. A scheme of passive and active damping of quadrupole vibrationsin the IR should be pursued.
13) IR Magnets
The IR magnets consist of 5 superconducting main quads, 3 permanent magnet quads, 2superconducting compensation solenoids and 32 superconducting correction coils. The
superconducting strands and cables are under development for various prototypes. The
superconducting compensation solenoids cancel the Belle solenoid fields. Since there is no
iron core in the superconducting quadrupoles, superconducting correctors placed around theadjacent vacuum chamber compensate the leakage fields from the quadrupoles. However,these correction coils also produce a field at the center of the quadrupoles. The impact ofthese fields should be evaluated carefully. The permanent magnet quads are made of SmCoand, because they do not need cryostats, allow the BPM’s and vacuum pumps to be as close
as possible to the interaction region. The permanent magnets require constant temperature to
maintain proper field uniformity. The group will carry out the required R&D and build
prototypes this year to keep the project on schedule. The Committee encourages beamsimulations with the measured fields.
14) IR Vacuum Chamber and Assembly
The new interaction region layout of the Nano-Beam scheme was presented. Starting fromthe boundary conditions imposed by the detector and by the magnetic insertion elements, thevacuum system has to be entirely redesigned. The insertion magnets will have a warm bore
vacuum chamber attached by bellows to the cryostats. Proposed positions for beam position
monitors, vacuum bellows and pumps were shown on the schematic layout. The nearest
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pumps can be placed at a distance of approx. 2.5 m from the IP. The operating pressure withthis configuration has been estimated to be in the range of 10-4 to 10-5 Pa. In a dedicated testwith the Belle Detector, an artificial pressure increase of this order of magnitude did not
result in an increased background rate. Nevertheless, this must be considered to be an
exceptionally high pressure for an interaction region.
The central part of the IP chamber can be shielded from direct synchrotron radiation from thelast bend. An updated estimate of the power levels shows that the adjacent beam pipes in thecryostats receive around 0.5 kW each and hence need to be water-cooled. It is proposed tointegrate the cooling ducts in the thin wall of the pipes in order to minimize the loss of space.
The central cylindrical Be-beam pipe of the interaction point is attached to the gradually
opening branching pipes, where the LER and HER beams merge together or separate. An
important cross section variation is seen by the beams, creating a local impedance, which has
been evaluated in a later presentation (see impedance estimation). A reliable estimate of the
HOM power dissipated in the central beam pipe has not been presented, but it could wellexceed the contributions from synchrotron radiation.
A very common problem with the design of IP vacuum systems is the ‘fight’ for space. The
space for machine components and for vacuum pumps inside the detector is extremely tight.
As a consequence, assembly and the required precise positioning of beam position monitors
are extremely difficult. The Committee encourages the KEKB team to continue the design
work and to search for innovative solutions, leading to an optimization that can only be theresult of an iterative design approach between all systems. A specific concern is the highpressure in the interaction point due to the lack of pumps. Again, this is not a unique problem
for KEKB. It should be recalled that solutions exist for integrated ion pumps operating in thefield of a solenoid, e.g. getter pumps integrated in the beam pipe and cryo-pumps.
With respect to heating of the vacuum chambers, the Committee expresses doubts concerning
the proposed water-cooling scheme that may result in either impractical or unreliable flow
conditions. A change of the proposed scheme may have implications for the cryostats andhence nontrivial design implications. The Committee also recommends studying thesolutions for this problem utilized by other laboratories, such as Cornell and SLAC.
15) Machine-Detector Interface
There has been considerable effort spent studying the effects of synchrotron radiation andparticle backgrounds in the detector. This is a very important first step. Direct illuminationof the central beam pipe is not a problem although future work needs to include scatteredradiation and the means for reducing this effect if it proves to be problematic.
Extrapolation of the backgrounds from an increase of the IR beamline pressure by a factor of
100 to 1000 is quite difficult. The present studies have shown that masking will be very
important and detailed simulations of the masking will need to follow the evolution of the IR
optics design. Machine studies measurements of backgrounds in the detector with IR
pressure bumps will be a very important calibration for the background and masking
simulations.
Space within the machine-detector interface has been shown to be at a premium. To allow
for as independent accelerator- and detector-hardware development as possible, care should
be taken to clearly define the physical volumes within this space, which are the domain for a)
the accelerators only, b) the detector only and c) where hardware for both will co-exist. In
addition to determining beam pipe cooling requirements and the implementation and therouting of cooling lines, some thought should be given as to whether temperature regulation
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will be needed for the beam pipe cooling. This may be particularly important for the beam
pipe through the permanent magnet quadrupoles and stabilization of BPM positions.
The Committee suggests that, if it is not in place at this time, a joint machine-detector
interface design team be established as soon as possible. At other laboratories, this approachhas been critical during the design, installation, commissioning and early operational phasesof similar projects. We suggest that this group should have a representative from both theaccelerator and detector sides, who are at a high level administratively to influence the design
efforts and resources from both sides. From the accelerator the Committee would suggestthat this team include members who have the following specializations: IR optics design,vacuum, operations, radiation-monitoring and controls/accelerator instrumentation. From thedetector we would suggest team members be included who can represent the following areas:
background simulations of synchrotron radiation and particles, the vertex detector, the central
tracking chamber, other major detector systems as needed, and the DAQ system. The chargeof this group is to forge a common vision, design and plan for the machine and the detector
interaction, which optimizes the overall interaction between the accelerator and detector andto oversee the installation and initial phase of operations. Some of the specific tasks of thisteam are to address remaining questions such as the background levels for the detector,
potential radiation damage of machine and detector hardware, the machine-detector angle,
vacuum and beam-pipe properties (including accelerator & detector installation), cooling,
access to and redundancy of components, radiation masking and monitoring, diagnostics for
operations, the ability of the detector systems to handle the higher trigger and backgroundrates. The team should also look carefully at solutions to these problems that have been
employed at other laboratories. Ideally it is best if the solutions that are found are ones thatall sides can “live with.”
Particular concern in the talks has been raised because the anticipated higher beam pipe
vacuum pressures due to the synchrotron radiation deposited, poor vacuum chamber pumping,as well as much poorer beam lifetime from losses due to beam-beam and Touschek scattering.
While it is the case for many detectors that a higher pressure in the center of the detector may
result in scattered beam particles impacting the vacuum chamber walls outside of the detector(reducing the detector background), this will need to be analyzed carefully for any IR optics
design and choice of masking. This is a very critical issue for the overall accelerator anddetector designs!
The effects of the electron-clouds within the detector should be analyzed, paying attention to
the sources of the electrons, their transport and impact sites. If the anticipated densities along
the beamline are significant, consideration should be given to the scattering of electrons andpositrons from the electron cloud and its potential for altering the dynamic aperture from nonlinear modifications of the focusing-functions in regions of large beta.
It may be possible to benefit from the higher deposited synchrotron radiation in theinteraction region. It has been observed that high synchrotron radiation dose levels and theright vacuum chamber surface material (one example, aluminum) after sufficient time tobeam process the vacuum and lower the secondary emission yield of the surface, will result ina synchrotron radiation stripe that will act as a getter. This is often referred to as “wallpumping.” As an example, at high currents and in the arcs of CESR, this represented asignificant increase in vacuum chamber pumping (~50 l/s/m) and resulted in lower beamlinepressures. This effect should be estimated for the IR designs. A plan for vacuum chamberconditioning during the beam current ramp up during commissioning should be formulated
and include the effects of radiation deposition in, and the long term damage to, the detector(esp. the SVD) and nearby accelerator components. It might be particularly useful if the

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initial round of commissioning and beam processing could take place with the detector
electronics powered down.
The Committee concludes the importance of a coordinated machine-detector effort must not
be underestimated. The correct understanding and modeling of detector backgrounds in thepresence of new accelerator and detector components is paramount to being able to achieve
the goals of SuperKEKB.
16) Vibration Measurement
For the Nano-Beam design, requirements to the LER/HER orbits’ offset at the IP are
unusually severe, especially in the vertical direction where an offset of about 10% of sigma-y= 56 nm may degrade the high-luminosity performance and whereas a sigma-y/2 offset is
unacceptable. Hence special care must be taken for the minimization of lattice magnet
vibrations and for an active, fast compensation of the collision offset with the orbit feedback.
In order to update and improve the characterization of the tunnel vibrations for KEKB
machine components that are to be inherited by SuperKEKB, a new series of vibration
measurements at KEKB have been performed mainly in the summer of 2009. The
measurements were undertaken with the superconducting quadrupoles of the final focus,
Belle solenoid and ring magnets turned off. Magnets, their supports and the tunnel floor were
tested with acceleration sensors at many locations around the ring, with particular attention to
the IR region, at different times during the day. The vibration amplitudes and power spectra
were recorded and analyzed in comparison with the 2003 data.
The conclusion is that at the IP the KEKB tunnel vibrates at 0.3 Hz horizontally and at 3 Hz
vertically. In addition, the magnets and QCS support system vibrate at 8 Hz. The measured
spectra roll off considerably in the frequency range 10–100 Hz. The correlation between
vibrations of different positions is reported to be negligible.
The vibration amplitudes of the IR magnets are much smaller than the size of the colliding
beams in the KEKB, that is ~2 µm vertically and ~100 µm horizontally, but comparable with
SuperKEKB, where sigma-y = 56 nm. The tunnel floor vertical vibration is ~70 nm forfrequencies >1 Hz; other components have even larger amplitudes. The contribution to thevibration amplitudes from the He flow is to be measured when the machine is running in May.
Since beta-y > 2.5 km in the final focus quadrupoles, their uncorrelated vibration amplitudes
are converted roughly 1:1 into the vertical collision offset, while the contributions from othermagnets’ vibrations are less important. So a special study of the IP orbit response to eachmagnet vibration is in order for the more accurate assessment of the total collision offset
caused by magnet vibrations.
In such a situation countermeasures are indispensable, e.g. in two possible areas: 1) Special
attention must be given to the mechanical design of the QC1 – QC2 support systems, where
the frequencies of the principal mechanical resonances should be tuned above 10–30 Hz andall possibilities to damp the mechanical response should be employed. 2) A fast IP-orbit
feedback system must be designed.
The Committee recommends the scheduling of an R&D study and the construction of a
prototype for the fast IP-orbit feedback system so it may be tested with beam as soon as
possible.
17) Injector Upgrade Overview & Positron Source
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The Injector Group plans to provide 4 GeV, 8 nC/bunch (= 4 nC x 2) positron beams to the
LER, by introducing an L-band capture section with either a flux concentrator or asuperconducting solenoid, followed by a 1 GeV Damping Ring. In the flux concentrator
scheme, the L-band sections would be displaced in a parallel beam line to allow the electrons
to bypass the concentrator. With the superconducting solenoid, the electron path does notneed the long target bypass but instead transits the solenoid. The focusing effect of thesolenoid on the electron beam should be evaluated. The flux concentrator scheme is underdevelopment with collaboration with BINP, but there seem to be more advantages to thesuperconducting solenoids. The final choice should be decided by comparison of prototype
test results of both schemes.
In order to achieve positron energy of 4 GeV, a second C-band section is required after thedamping ring. For the L-band capture, the group has developed 40 MW klystrons andaccelerating sections of 10 MV/m. The damping ring is an essential part of producing lowemittance positron beams. On the other hand, a photocathode RF gun is being developed forintense low-emittance electron beams. The Committee strongly encourages the necessary
R&D activities to support the damping ring construction.
18) RF Gun
The argument for an RF gun for the production of low emittance electron bunches as the mostcost-effective solution was certainly clear. The interest in having a cathode surface with thelongest possible lifetime seems to point to copper as the cathode material. However, thecommittee thinks that it is very optimistic to expect the cathode to survive more than several
weeks with the emission of 1 nC bunch charges even assuming the presence of 10-9 to 10-8 Pa
vacuum levels. So the gun structure should be designed to allow for the easy, rapid changing
of cathodes.
Increasing the quantum efficiency for a copper cathode will lower the incident laser power,
reduce long-term damage to the cathode, and therefore raise the cathode lifetime. The idea
for increasing the efficiency by reducing the wavelength of the laser to approximately 200 nm
is reasonable for a test. The plan to produce the highest accelerating gradient from a ½ cellnormal conducting S-band RF cavity also is a reasonable design to consider.
The committee sees this effort as important for the SuperKEKB project and for RF gun
research for the accelerator community at large. It recommends careful assessment of theresources and effort require for this study: the design of the copper RF structure with
sufficient pumping to maintain the necessary ultra-high vacuum, the selection of a laser(locked to the RF frequency), the design of the laser’s optical systems, the design of the RF
coupler, the selection of the needed RF source and power amplifier, and sufficient diagnostics
to measure the cathode’s performance both during initial testing and operations. The
committee also suggests that the effort for this project not be underestimated, as experiencefrom other laboratories has shown developing expertise in RF photo-cathodes requires
significant time and resources.
19) Damping Ring
The design of the positron damping ring is innovative and fits nicely within the scale of thelinac and the site constraints of KEK laboratory. Careful engineering details were shown
including the lattice, magnet designs, vacuum duct design, and injection extraction. The
circumference appears longer than other similar damping rings in the world owing to the

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reverse-dipole bending scheme of the lattice. The budget of the accelerator components of thedamping ring is about 30 M$ which should be adequate for the task. The committee discussed
whether the design could be simplified to reduce the size of the ring in order to reduce thecost of components and the overall size of the new tunnel and overhead support building.
The accelerator physics aspects of the damping ring were discussed and all the major topics
were covered in detail. The outstanding issue the committee saw was reducing the harmonic
multi-poles of the magnets, which was shown to reduce the dynamic aperture of the injected
beam. Further work is needed on the dynamic aperture and magnet specifications of thedamping ring.
The requirement to be able to inject up to 8 nC charge per bunch seems to the committee toperhaps be larger than needed. This charge will likely only be needed if many new systems
work perfectly and there are many fills from scratch of SuperKEKB. In the top-up mode
during collisions, the SuperKEKB rings will need and want far smaller bunch charges to keep
the currents constant.
20) Beam Transport, Injection, Extraction from DR
Simulations show that the positron beam produced by an electron beam of 10 nC at the Lband capture section is more than 10 nC. However, the beam is so large that it requires an
Energy Compression System for injection into the damping ring. Assuming 80% efficiency
for injection to the damping ring with a momentum spread of <1.5%, an 8 nC positron beamwould be produced in the damping ring. Because of radiation safety concerns, the group plans
to start operation with 4 nC, 120 MeV beams. For extraction, a double kicker system is toguarantee that the two bunches are placed on the same trajectory. A bunch compression
system is employed to obtain 0.5 mm long beams just after extraction from the damping ring.
At the end of the linac, an ECS system is also required for the transfer line to the LER. The
group plans to study detailed electron trajectories in this new arrangement. The Committee
fully endorses the planned simulations and prototype R&D.
21) RF Overview
The performance specifications for the Nano-Beam version SuperKEKB, while lessdemanding of the RF system than the high-current version, are nonetheless significantly moredemanding than those of the existing KEKB. In particular, beam power in the LER is
increased by nearly a factor of three, due to the increase in beam energy and current, whilecircumferential voltage is increased by only 5%, leading to a substantial increase in beamloading. In the HER, beam energy is reduced by 12.5% while current is increased by 87%
and the circumferential voltage is decreased by more than a factor of two. Beam loading in
the HER becomes very severe. A straightforward extrapolation of the existing system would
require unfeasibly large input coupling and cavity detuning frequencies larger than therevolution frequency. The last condition would result in unacceptably rapid growth of the -1
mode instability.
The RF team has been exceptionally creative, reconfiguring existing equipment with only
modest additions to meet these stringent new requirements.
In the LER, removing two ARES cavities and adding 8 klystrons creates a system of 18
ARES cavities, each with its own 800 kW klystron. In this configuration, each station can
comfortably supply the needed voltage and power with a readily achievable input coupler,
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while maintaining a sufficient reserve and instability growth times that are manageable withexisting feedback and damping systems.
An even more challenging situation in the HER is very elegantly handled by invoking theconcept of “reversed-phase operation”, in which four of the ARES cavities are removed, allremaining ARES cavities are provided with individual klystrons and some of thesuperconducting cavities are switched to the opposite side of the crest of the RF wave. Allremaining cavities can then be operated at higher gradients, with much reduced beam loading
demands, including instability issues, detuning angles and input coupling.
This
implementation, which works because of the high beam loading, is preferred over a scheme
using 14 ARES cavities without superconductivity, which would also work, partly because
the existing SC cavities and cryogenic system can be used essentially unchanged, but mostly
because use of SC technology reinforces KEK’s world leadership in that technology. The
non-SC solution is preserved as a back-up scheme.
The doubling of the beam current means that the phase transient driven by the abort gap of
500 ns would be twice as large as the presently accepted 3-5°. This will be straightforward tohandle by reducing the abort gap to 200 ns and using faster abort kickers. KEK has been aleader in developing the fast (< 10 ns) kickers required by the proposed ILC damping rings.
While this plan meets operational requirements, reliable implementation will require thedeployment of the advanced digital Low Level RF control circuitry being developed by KEK
and its industrial partners, in parallel with most other accelerator laboratories around theworld. Hardware design is nearly done and the first system will be installed and tested later
this year. The only proposal that is of some concern to the committee is the suggestion thatsome of the RF systems would continue to be operated with the old analog LLRF control.
The reliability and simplicity of operation achieved by a having a common system seem
worth the additional 10 Oku-yen.
The design of the RF system for the damping system is also underway. The basic ARES
cavity design will be used, but stripped of its storage and coupling cavities, which are notneeded because the stored current is so much less than that of either of the Main Rings.
The committee wishes to compliment the RF team for the very innovative and efficient way
in which they have met all the RF requirements of SuperKEKB!

22) ARES Cavity
The reconfiguration of the RF system for the ARES cavities to one klystron per cavity has
already been described. With the exception of increased HOM power, the operating
characteristics of the cavities in the LER are essentially unchanged, and continued successful
operation is a reasonable expectation.
Multipacting in the coaxial section of the input coupler has been observed in about 10% of
the ARES cavities in use in KEKB. To eliminate this concern for the higher power operationof the couplers for SuperKEKB, fine circumferential grooving has been applied to the insideof the outer conductor, and successfully tested and used in actual KEKB operation. In
addition, the increased input coupling factor required for SuperKEKB has been demonstrated
in low power tests. High power tests are scheduled for April, and installation of the newcoupler on an operational ARES cavity for May

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The HOM waveguide loads will still have a 50% margin to their design limits. The Grooved
Beam Pipe (GBP) loads will have a 30% margin with respect to their measured performance
limit at 1200 W. Nonetheless, the higher power GPB loads being designed for the Damping
Ring accelerating structure can be used here, if needed.

23) Superconducting Cavity
The feasibility of “reversed-phase operation” of the superconducting HER cavities is criticalto the RF system plan for Super KEKB. Only by using this technique can the new RF
demands be supported by existing hardware without major changes. By analysis and carefultest, the KEKB RF group have examined the issues and determined that none of them will
prevent implementation of this concept; synchrotron tune, beam loading response,
controllability, bunch length and transient trip response are all either unchanged, or ifchanged are acceptable and controllable. Tests included support of a luminosity run at
1200 mA delivering 300 kW/cavity to the beam. The only unusual event was a rise in cavity
voltage on a reversed-phase cavity during a beam energy change. A thorough investigation
demonstrated that this was to be expected, and that the range of possible excursions at thenominal operating point is well within the tolerable operating range of the superconducting
cavities.
HOM dampers will have to be improved to deal with beam currents in excess of 2 A, but thisshould be achievable with straightforward extensions of the existing design. Design concept
tests were successful and prototypes are being constructed for further proof.
Although the existing input couplers will meet the RF power requirements of SuperKEKB,
further development of couplers for higher power is ongoing.

24) RF Accelerating Structure for DR
The ARES accelerating cavity, relieved of its coupling and storage cavities for use in thedamping ring, needs to be dimensionally adjusted to correct for the frequency changes causedby those removals. Changes in cavity diameter must be accompanied by rotation of the input
coupling loop to achieve the correct coupling factor at the right frequency. This design andanalysis task has been completed, and the geometry is settled.
HOM power will be handled by replacing the SiC tile-loaded GPB with directly cooled SiC
bullets in a winged chamber capable of handling 5 kW. Analysis has identified the optimal
position and angle for the bullets, subject to the mechanical constraints imposed by beam
pipes and flanges. The fact that the cavity is provided with a single slug tuner creates a slightasymmetry in the fundamental electromagnetic accelerating mode and some leakage offundamental power into the HOM load. The effect has been thoroughly investigated and the
maximum effect is less than 2% of the load thermal rating. High power tests are planned totake place soon.
Investigations of higher order modes of the complex RF structure have been carried out, andthe most troublesome mode, at 11.75 GHz, has a comfortably long growth time of 30 ms.
25) Vacuum

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With the Nano-Beam scheme as the new base line for the SuperKEKB, several importantdesign parameters have changed for the vacuum system. In the LER the lower beam currentof 3.6 A and the increased arc bending radius of 71 m give a reduced power load to thevacuum chambers. In the HER the lower beam energy of 7 GeV combined with the reduced
beam current of 2.6 A result in a considerable reduction of the synchrotron radiation load on
the vacuum chambers. The longer bunch length also lowers the HOM power. Compared withthe present machine the new parameter set is still very severe but, nevertheless, opens up
several new design options. Therefore, copper beam pipes, as they were shown to the last
MAC, are no longer the only choice but, depending on the location in the machine, aluminumand other materials could be used. This widens the choices for design, manufacturing andprocurement of the vacuum components.
It is proposed to install newly designed beam pipes and other main vacuum components for
the LER and for the HER arcs. Some of the existing equipment like ion pumps will be reused.
It is proposed to replace the NEG pumps since they have a limited capacity. A new designfor the pumping ports, bellows and other components will reduce the global impedance of therings. A strong reduction of the global impedance budget results from the use of beam ductswith an antechamber. This design would in principle no longer be required with the reduced
synchrotron radiation load but it provides a low impedance. It is proposed to maintain thevacuum chamber aperture from the high current design (94 mm) so that chambers fit into
existing and reused magnets. A decision on this point is still open.
The electron cloud will remain an important consideration in the new design. Therefore, all
the measures previously studied and proposed for the high-current version like antechamber,surface coatings, solenoids, clearing electrodes, and a grooved surface will be used for thedesign of the new vacuum system. The threshold for single bunch instability defines anelectron density of 1x1011 m-3, which has been taken as the design value for the LER. The
estimated electron densities in the arcs exceed the threshold for instability by about a factorof 50. The main contribution (~93%) comes from drift spaces and steering magnets. It is
proposed to use all of the various established measures to come below the threshold. The
most promising solution consists of a combination of solenoids in the drift spaces, grooved
surfaces in bending and wiggler magnets, and possibly TiN coating for the copper chambers.
For an aluminum chamber, a surface TiN coating remains indispensable. The best results
have been obtained with specially designed clearing electrodes. Unfortunately, this solution isvery delicate and expensive. Longitudinal grooves are by comparison much easier to produce
specially with an extruded aluminum pipe. This solution will be evaluated with a test
chamber during the next run.
Among the outstanding issues are the design of special components and a decision on the
cross section. Is proposed that the beam ducts for the HER will use the same components as
the LER. The schedule shown to the committee includes a total of about 2000 beam ducts
between 2 and 6 m long that have to be manufactured and installed. This will require wellestablished procedures for manufacturing, baking, vacuum testing, solenoid winding andinstallation.
The committee is impressed by the considerable progress that has been made since the last
MAC and specifically, since the change to the new base line. It must be recognized that for
the vacuum system it has essentially been a new starting point in the design that requires afundamental reorientation. For this reason some of the choices presented to MAC my notwithstand a critical scrutiny. Among the most obvious items is the traditionally very tightinterrelation between magnet and vacuum systems. The committee recommends a combined
effort between magnet and vacuum groups to arrive at a common design.

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A decision on the aperture and vacuum chamber cross section is urgently needed.
The choice of the vacuum chamber material is important since it has wide-ranging
consequences from material properties to procurement and manufacturing. With limited
resources, it may be preferable to adopt one common solution for both rings. The committee
believes that the basic design concepts have all been validated and are ready to be chosen.
The means to mitigate the electron cloud are a specific example.
The new design and layout of the insertion is in a first stage of iteration. To advance thedesign, the committee recommends a combined effort between machine and detector
specialists.
26) Magnets
The presentation of the main ring magnet system was very well organized; its overall
description of the current scope of work seemed quite complete. In the latest optics designfor the LER and HER, a very large number of new magnets will be required: the lengths ofthe dipole magnets for both rings become nearly the same length, and more wiggler magnets
with shorter poles, more bend magnets, quadrupoles, sextupoles and steering correctors areneeded for the approximately 30% more HER cells. A larger capacity water cooling system
is required for the added heat load and almost all of the magnets will need to be removed,
refurbished, tested, have magnetic field measurements performed, their support base-plates
replaced, the magnets and stands replaced, be surveyed, connected to power supplies andtested. While some of the power supplies may be reused, specifications for many havechanged; some will certainly need to be replaced or upgraded, new power supplies (andbuilding space) are needed for the additional magnets in the optics, and the cable plant will at
least need servicing and likely replacement or upgrade. With the construction of newmagnets out of different runs of steel and using different dies, the magnetic characteristics
will be different, requiring the different magnet families be placed in common magnet power
supply strings – likely adding to the number of magnets to be constructed.
Removal and reinstallation schedules will be constrained by the vacuum system work, therequirement to not disturb certain accelerator components and systems (e.g. the RF cavities)
and the need to stage the disassembly and reassembly to make use of the accelerator tunnel asa storage site for magnets, while not being refurbished, tested or measured. Having proper
tools and fixtures for moving magnets and surveying them may also impact the schedule
positively. For example, perhaps special lifting fixtures, which can straddle one beam line topluck a magnet from the other beam line, or a transport fixture, which does not requiresignificant repairs to the floor for operation, might be useful in reducing delays to theschedule.
Improvements to survey and alignment were described and the committee feels these will bevery important for the placement of accelerator elements. While the simulation of placement
errors for optical elements in the final lattice layout needs to be completed, experience inother laboratories underscores the importance of accurate alignment and mechanical stabilityof magnets in order to approach single-beam emittance coupling values of 0.3-0.4%. The
study of vibrational modes in the magnets and their supports and their relative motion withrespect to the floor, the ground and the other ring’s components is critical for theunderstanding and operation of position and collision alignment feedback loops. For theseendeavors the magnet group and feedback group need to be in close communication.
The committee recognizes the large effort required by the magnet group in the current designof the lattice. The Committee’s first recommendation is that a closer connection between the
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lattice design group and the magnet group be established to allow magnet hardware
considerations to be taken into account in the optics design. For example, any effort made tostandardize magnets and reduce the number of different types will have a significant impact
on the magnet system workload. A few possible ideas to explore are: 1) The present design
has the LER and HER dipoles almost the same length; could they be the same? 2) Is it
possible to reuse a combination of the present HER and LER dipoles alternately in either the
HER or LER cells by allowing the cell symmetry to be broken? While it is unavoidable tobuild new magnets for SuperKEKB, the benefits of reducing this effort need to be aconsideration in the optics design.
As the effort for recreating the magnet layout for SuperKEKB is massive, the committee also
recommends that adequate resources (personnel, financial and space) be provided toaccomplish the task. If this is not done effectively, the magnet workload could become thecritical path for the project’s schedule.
27) Beam Diagnostics
A comprehensive survey of diagnostic needs for the SuperKEKB has been initiated. The
Committee commends this effort.
A button electrode has been designed for the SuperKEKB BPMs with a small diameter of
6 mm. The prototype is being tested at KEKB. The signal-to-noise ratio of thesuperheterodyne detector has increased from 61 to 88 db after several recent improvements.
The BPM accuracy requirements are presently simply copied from those of the KEKB. All
system designs follow from this assumption. It is strongly recommended that the diagnostics
requirements specific to SuperKEKB be defined as soon as possible. These requirements
cannot be fully specified until the lattice is fixed. However, as the lattice firms up, theyshould be provided to the diagnostic team in a timely manner so that the subsequent design
work on diagnostics systems can proceed without delay. Iterations for the design
requirements are then expected as the lattice design progresses in time.
The fast ion instability growth rate is estimated to be 0.3 ms for the HER. The electron cloudinstability growth rate is estimated to be 0.5 ms for the LER. The growth rates of various
longitudinal instabilities are generally found to be slow, although the LER is still envisioned
to require a longitudinal feedback system. These growth rates form the present basis for thedesign of the transverse and longitudinal feedback systems. However, more work is needed to
sharpen up on the predictions of these instability growth rates, and as that happens, thefeedback systems design should evolve.
Vertical beam size measurement using an interferometer is at the limit of the interferometer
resolution. Reflection mirrors, although much more relaxed than in the high current scheme,
will require some serious design work. A prototype will be tested on KEKB. A straightradiation X-ray monitor for vertical beam size measurement is considered with resolution ~510 micron.
An interesting idea of a beamsstrahlung monitor is being considered. It is estimated that there
should be a large number of beamsstrahlung photons that can be used to measure beamcollision sizes.
It is planned to monitor the multi-bunch operation by providing a pilot bunch at the end of abunch train. The Committee suggests considering the possibility of double pilot bunches, one
ahead and one behind a bunch train, because the difference between these two pilot bunches
can give information on effects such as ions, cloud electrons, and wake fields.
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Collision optimization is assured by a feedback system around the IP. It is suggested that amore careful evaluation of the Nano-Beam configuration be performed for this feedback
operation—in particular, whether this system will only feed back on the vertical beam offsets
or it is also capable of feeding back on the horizontal offsets, and in either case, what are the(possibly complicated) beam responses as functions of beam offsets.
It is suggested that a means be provided to monitor BPM vibrational motion relative to its
nearby quadrupole center.
28) Impedance Estimation
For a number of SuperKEKB LER vacuum duct components, evaluation of loss factors andlongitudinal impedances has been carried out using the GdfidL code. For a bunch length of
3–10 mm a reasonable longitudinal wake length of 0.1 m (for the loss factor) and 5 m (for thelongitudinal impedance) was computed.
In the comb-type bellows (1000 units) the loss factor is computed as a function of the bunch
length, in the above-mentioned range, showing 2.2 V/pC at 6 mm, while all of the curve lies
below the present KEKB level. However, a couple of trapped modes were discovered withthe frequencies above cut-off. The synchrotron radiation masks on the outer sidewall of theantechamber gives a negligible contribution; the same is true for the perforated screen
covering the NEG side of the antechamber and for the flange connections.
The following reported loss factors are so far evaluated at the 6 mm bunch length only. 16
movable masks with taper sections on both ends give 3.7 V/pC, being the largest vacuum
component. From the 2.2 km round resistive pipe we have 1.7 V/pC for Cu or 2.3 V/pC for
Al. BPMs and the bunch-by-bunch FB BPM have been designed especially for the highcurrent SuperKEKB option and thus their contribution to the loss-factor budget is small, as is
the contribution from the crotch IP chamber, both with 20 mm and 30 mm diameter joints.
However, a vertical beam displacement in the IP duct excites many trapped TE modes; theirimpact on stability of the 2503-bunch beam is planned for further study. All thosecomponents so far evaluated (together with the ARES cavities) contribute ~18 V/pC to theloss-factor budget, which results in ~900 kW HOM power loss at 3.6 A current in the LER
with the Al duct, and somewhat less (~880 kW) with the Cu chamber.
The next items planned include estimation of other components such as injection section andinteraction region, using the obtained impedances for evaluating beam instability increments(specifically, from bellows and movable masks), and calculation of loss factors andlongitudinal impedances of the HER components.
The Committee recommends speeding up the evaluation of the loss-factor/impedancecontributions which are as yet unknown in order to provide reliable specs for the LER RF
design which has to have sufficient allowance for the HOM power loss.
Smallness of the vertical emittance strengthens the limits on the coherent vertical instabilities
of any kind; therefore the Committee puts the emphasis on timely evaluation of all importanttransverse impedances with the priority on the novel components, e.g. clearing electrodes orgrooved walls envisaged for reduction of SEY, where the preliminary results indicate aserious enhancement of the kick factor caused by the misalignment of the groove direction.
The wake-fields should be incorporated into the tracking simulations for the ring to evaluate
the impact of the wakes on the transverse (esp. vertical) distribution.

Page 22of 2729) Beam Abort System
The concept of the beam abort system for SuperKEKB is described. The beam abort system
must have a fast rise time to cope with the abort gap of <200 ns which has been required by
the design. A list of the design parameters of the abort system was shown. The proposedsystem consists of a fast, pulsed kicker with a water-cooled ceramic vacuum chamber. The
extracted beam traverses first a thin Ti window, followed by a Lambertson magnet. The
extracted beam passes through air and is absorbed in the dump block. In order to reduce thepower density on the titanium window, it has been proposed to orient the window at 45˚ withrespect to the beam. As a further step to cope with the high beam density in the SuperKEKB,
it is proposed to add a pulsed quadrupole in front of the window that defocuses the beam as it
sweeps across the extraction window. The power supply for the kicker magnet has therequested 120 ns rise time. The Committee was shown results from a test with a 1 mm
Titanium window exposed to the KEKB beam. The preliminary results confirm that thewindow can withstand the SuperKEKB beam currents, but without a satisfactory safetymargin.
The Committee encourages the KEKB team to continue with the detailed design and to
improve the safety margin. The window thickness as well as choice of material, e.g. astronger titanium alloy or beryllium, could be optimized. It may also be possible to add
another pulsed magnet, which has a ramped deflecting field during extraction, and to movethe window downstream of a defocusing quadrupole to further “fan out” the bunches. The
Committee also suggests looking into the coated ceramics used in CESR and LEP. The
Cornell coated ceramic chamber was capable of passing a 40 nsec rise-time deflecting
magnetic field. Perhaps an adaptation of this design would be applicable.
30) Control
The control system for SuperKEKB is envisioned to be EPICS based, as it is in KEKB. The
KEKB control system is currently being upgraded to a more recent EPICS version. This
involves upgrades of the IOC, which allows EPICS to be embedded in various devices, aswell as upgrades in OPI host computers and the network switches. The old CAMAC fieldbuses are mostly to be progressively replaced. Ethernet-connectable modules will replace themagnet power supply interface. For SuperKEKB, the application programs will also be
updated, with the interface with the applications provided by linking a person from the
hardware group with someone from the control group. It is envisioned to provide additional
manpower by collaborations with commercial companies and foreign laboratories.
Continuing along the path of the present KEKB upgrade route is a reasonable and necessary
approach in preparation for the SuperKEKB. To speed up the process, it is suggested that
inputs from various hardware groups be sought anticipating the operation of the SuperKEKB
and that these inputs be integrated into specifications for the control system in a timely
manner.
Some "software" support will likely be needed during the creation of EPICS control panels
for the hardware groups, which have major component changes. This may be necessary sincethose groups will be undertaking a large number of tasks in the design, production,
testing, and installation of new hardware, and at the same time have a large number of related
control panel changes. When looking across working groups, it will be the ones with thegreatest workload who will also have the greater number of software modifications. So
in an effort to bring the workload into more of a balance, these groups with the greater

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amount of work should be provided with software support from the control group or
elsewhere.
31) Facility and Infrastructure
The presentation for the scope of work for the facilities and infrastructure was well organized
and relatively complete. Although it does need to be updated to reflect the present design for
the accelerator, the conclusions will not likely be fundamentally different from thosepresented: Additional space will need to be located temporarily for storage of components
removed from the accelerator, for modification, construction and testing of components andpermanently for additional infrastructure such as new magnet power supplies, added coolingand electrical capacity.
The committee agrees with the general conclusions for the requirements for temporary andpermanent space for facilities and for the increase or upgrade of the cooling and electricalinfrastructure. The effort in this capacity needs to be linked to the various groups that itsupports (e.g. vacuum, magnet and power supply) before estimates can be finalized for theneeded support facilities and services. The lack of a clear up-to-date plan can complicate ordelay the implementation of the overall project schedule.
32) Schedule / Budget / Human Resources
The overall R&D and construction schedules for SuperKEKB were shown, and the details
discussed. The plan is for a 3.5 year construction time starting mid-year in JFY2010. The
overall schedule looks well thought out and complete. It appears to have a good chance ofbeing able to be carried out if the funding is provided as proposed. There is some uncertainty,
however, because the funding profile for each year is not really known.
The overall budget as shown at first look seems to be adequate although tight with little
margin to complete the project. However, as the accelerator tasks are better defined, thebudget details need to be worked out in more depth. Contingency planning for unforeseen
events should be built into the budget or if the funding versus year is not as requested.
The tightest part of the schedule is the removal and reinstallation of the tunnel components
including the magnets, supports, and vacuum beam ducts. The planning for the schedule forthese activities should be taken to the next level of sophistication to resolve potential conflicts
with resources. Interferences with other laboratory resource needs should be determined andtaken into account.
If the SuperKEKB funding arrives as planned, the number of people available to design andplan the project is too small. A staff of about 82 people is needed for SuperKEKB at the peakof construction. With the present staffing it is anticipated that there will be about 48 people
available at the time. Thus, 34 new people need to be redirected or hired to construct the
project on time. Where these people will be found is a subject of ongoing discussions. A
laboratory wide strategy for staffing would help with this issue.
Finally, the cost of controls and diagnostics, e.g. beam position monitors, appears to behigher than can be accommodated. A reduced scope plan or new technical solutions should
be investigated.

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Appendix A
KEKB Accelerator Review Members
Andrew Hutton

JLab, Chairman

Mike Billing

Cornell (replacing Dave Rice)

Alexander Chao

SLAC

Warren FunkJLabOswald Gröbner

CERN (retired)

Trevor Linnecar

CERN (unable to attend)

Won Namkung

PostechFlemming Pedersen

CERN (unable to attend)

Eugene A. Perevedentsev

BINP

David Rice

Cornell (unable to attend)

John Seeman

SLAC

Wang Shuhong

IHEP (Unable to attend)

Katsunobu Oide

KEK, Ex Officio Member

Kazunori Akai

KEK, Secretary, Accelerator

Haruyo Koiso

KEK, Secretary, Accelerator

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Appendix B
Agenda of the 15th KEKB Accelerator Review Committee

February 15-17, 2010
In the meeting room on the first floor of Building No.3, KEK Tsukuba, Japan
Date / Time

Subject

PresenterFeb. 15 (Mon)8:30 - 9:00

Executive Session

9:00 - 9:20

KEK Roadmap

A. Suzuki

9:20 - 9:50

KEKB Status

Y. Funakoshi

9:50 - 10:20

Belle & Belle-II

T. Higuchi

10:20 - 10:40

Simultaneous Injection

K. Furukawa

10:40 - 11:00

Coffee Break

11:00 - 11:20

Operation Experience of Crab Cavity

Y. Yamamoto

11:20 - 11:40

Nano-Beam Scheme for SuperKEKB

H. Koiso11:40 - 12:20

Machine Parameters

Y. Ohnishi

12:20 - 13:30

Lunch

13:30 - 13:50

Beam-beam Simulation

K. Ohmi

13:50 - 14:05

Fringe Field of Solenoid

K. Oide14:05 - 14:50

Lattice Design

A. Morita

14:50 - 15:10

Systematic Study of Nonlinear Dynamics

E. Levichev

15:10 - 15:30

Coffee Break

15:30 - 15:50

IR Overview

M. Tawada

15:50 - 16:10

IR Magnets

N. Ohuchi

16:10 - 16:30

IR Vacuum Chamber and Assembly

K. Kanazawa

16:30 - 16:50

Machine-Detector Interface

M. Iwasaki

16:50 - 17:10

Vibration Measurement

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H. Yamaoka /M. Masuzawa

Feb. 16 (Tue)
8:30 - 9:00

Executive Session

9:00 - 9:20

Injector Upgrade Overview & Positron Source

T. Kamitani

9:20 - 9:40

RF GunT. Sugimura

9:40 - 10:00

Damping Ring

M. Kikuchi

10:00 - 10:15

Beam Transport, Injection, Extraction from DR

N. Iida10:15 - 10:35

Coffee Break

10:35 - 10:55

RF Overview

K. Akai

10:55 - 11:10

ARES Cavity

T. Kageyama

11:10 - 11:25

Superconducting Cavity

Y. Morita

11:25 - 11:40

RF Accelerating Structure for DR

T. Abe11:40 - 12:20

Vacuum

Y. Suetsugu

12:20 - 13:30

Lunch

13:30 - 14:10

Magnets

M.Masuzawa

14:10 - 14:50

Beam Diagnostics

H. Fukuma

14:50 - 15:05

Impedance Estimation

K. Shibata

15:05 - 15:25

Coffee Break

15:25 - 15:40

Beam Abort System

T. Mimashi

15:40 - 16:00

Control

T. Nakamura

16:00 - 16:20

Facility and Infrastructure

M. Ono

16:20 - 16:35

Schedule / Budget / Human Resources

K. Akai

16:35 -

Executive Session / Report Writing

Feb. 15 (Wed)
8:30 - 11:00

Executive Session

11:00 - 12:00

Close-out

12:00

Adjourn

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