The Seventeenth KEKB Accelerator Review Committee Report
March 7, 2012
Introduction
The Seventeenth KEKB Accelerator Review Committee meeting was held on February 20-22,
2012. The following members of the Committee were unable to attend: John Fox (who wasable to connect via EVO), Stuart Henderson, Dave Rice and John Seeman. 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 high standard of the presentations, which dealt with theearthquake recovery as well as the design of SuperKEKB. It was particularly pleasing to haveseveral presentations given by recently hired junior staff members. The Committee evaluatedthe present 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-acc.kek.jp/kekb/.
Contents
A) Executive SummaryB) RecommendationsC) Findings and Comments
1)
KEK Roadmap
2)
Recovery of Linac after the Earthquake
3)
Overview of Design Issues
4)
Overview of Construction Status
5)
Belle II Construction and Commissioning
6)
Dynamic aperture and IR modeling
7)
Error Tolerance and Optics Correction
8)
IR Magnets
9)
Beam Background
10)
IR Vacuum Chamber and Assembly
11)
Collision Feedback
12)
Magnet13)
Beam diagnostics, Feedback systems
14)
Photon Monitors
15)
Beam Background16)
Development of New LLRF System
17)
Improvement of Superconducting Cavities
18)
Cavity for Damping Ring
19)
Production Status of Vacuum Components
20)
Baking equipment and coating equipment
21)
RF Gun and Low Emittance Transport
22)
Positron Source
23)
CSR in Damping Ring
24)
Synchrotron Injection
25)
Beam Abort System
26)
Control and Timing System

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A) Executive Summary
The SuperKEKB Project has made considerable progress since last year despite the massive
earthquake that did considerable damage to buildings and equipment. However, the effort
applied to a rapid recovery of the linac and Photon Factory was not available to makeprogress on the project, so all the schedule float has already been used up. There has been
rapid progress in some areas, for example the vacuum system, with large quantities ofcomponents being delivered; this has overloaded the staff assigned to inspection and quality
assurance. In other areas, notably the Interaction Region components, the very specializedcomponents are still being designed, and should be prototyped before going out for finalorder. The schedule is extremely tight to complete everything in the time available. The
progress in the linac area is impressive; the earthquake caused considerable damage to thelinac, but the linac group managed to resume beam operations within two months. In
addition, the new linac is designed and components are on order. Magnet refurbishment isproceeding; the wiggler magnets survived being banged together in the storage area, but it isfeared that the LER Magnets did not fare as well. Progress in the design and beam dynamics
of the rings has been steady, but this is an extremely difficult machine and there are stillunanswered questions.
Overall, the Committee considers the cost risk for the entire Project to be low; and thetechnical and schedule risks are considered low for the Injector chain, facilities and the ringcomponents, but the committee considers the technical and schedule risk high for theInteraction Region. The committee therefore believes that a mitigation strategy should be
developed, modifying the commissioning plan to enable the project to reach T=0 on time andto advance the start of physics operation as much as possible.
B) Recommendations: The Committee has made recommendations throughout thedifferent sections below. Highlights of these recommendations are summarized here.
1) Develop a back-up plan to commission the collider rings without the Interaction Region
components to establish the required beam current, to carry out low emittance tuning andto approach the required vacuum by beam scrubbing of the ring. This plan would be
activated in case of delays in delivery of the interaction region components to minimize
the impact to the start of the physics program.
2) KEK management should continue to do everything possible to ensure that the staffing
needed for SuperKEKB is made available as soon as possible. Some progress has been
made by short-term and some permanent hiring, and through collaborations with
universities and other institutes, but shortage of qualified staff continues to be a majorrisk to successful completion of the project, the commissioning and operations.
3) Develop a clear set of milestones for the production of the IR SC magnets and cryostatsso that progress can be carefully tracked and the high schedule risk, which concerns thecommittee, can be mitigated.
4) Re-examine the IR Vacuum design to ensure that the vacuum required for the experimentcan be obtained in a reliable way. It is also necessary to find sufficient space andaccessibility for vital machine elements.
5) Develop, with benchmarking, the necessary simulation tools to study the various criticalpath beam dynamics effects impacting SuperKEKB performance. These simulations
should include at least the 3D IR modeling, the error effects, dynamic aperture, beam-

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beam interaction, intrabeam scattering, and the outcome figures of merit including theachieved luminosity, detector background, and Touschek lifetime.
6) 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 of aself-consistent end-to-end description of the injection system that meets all of therequirements.

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C) Findings and Comments
1) KEK Roadmap
The KEKB management will be renewed at the end of March, with Prof. Katsunobu Oide
retaining his position as Head of Accelerator and Prof. Nobukazu Toge, well known to thecommittee for his work on ILC, will be a KEK Trustee. In addition, several of the otherappointees have been strong supporters of the B Factory program at KEK, for example, Prof.
Masanori Yamauchi, Head of the Institute of Nuclear Science.
The existing Roadmap was presented and it is clear that the direction of the laboratory has
been following the program that was set out. The Roadmap will be renewed in 2013, and thiswill establish the direction of the laboratory for the following five years. This will cover thestart of the SuperKEKB physics program, but will also be the time that ILC could become an
option for Japan.
2) Recovery of Linac after the Earthquake
An earthquake if magnitude 9.0 on the Richter scale struck the northeastern coast of Japan on
March 11, 2011. The buildings and accelerators of KEK experienced an acceleration of
0.34g, which lasted for more than 3 minutes in the Tsukuba area. Even though the strength ofthe earthquake was not extreme, the long duration caused serious damage in KEK.
The 600 m linac tunnel was severely damaged, and the maximum movement of some
supporting girders reached 10 cm longitudinally and 6 cm transversely. A section of a
focusing triplet fell on the ground, and bellows and BPMs were deformed and seriously
damaged. The Linac system was vented to air, and cooling water flooded the tunnel. There
are 60 klystron-and-modulator units in the klystron gallery, and several units experienced
vacuum leakage, ceramic window leakage, broken hybrids and waveguide leakage.
Excellent decisions were taken to reduce further damage to the Linac system, especiallyback-filling dry nitrogen into the vacuum system during the power outage period. The
excellent decision-making and teamwork recovered 3/8 of Linac within two months. Afterthe repair work, the Linac system was conditioned and reached a trip rate comparable to theoperation records before the earthquake. 3 GeV electrons were injected into the Photon
Factory on May 16, and injection into PF-AR on June 1. The remaining 5/8 of the Linacvacuum was recovered by the end of October, and high-power tests were done with no major
problem in December. The upstream Linac section will continue to be upgraded as part of
the SuperKEKB project.
Structural analysis of the Linac supporting structure showed a resonance frequency of 3.5 Hz
after the shock. Reinforcement of the girder and insertion stopping-block to limit theoscillation amplitude was implemented to increase the stiffness of the girder system. This
would be very useful in any future earthquake. This experience should be applied toSuperKEKB magnet support girders.
A great portion of manpower and resource was devoted to the recovery after earthquake last
fiscal year. The committee would like to give high marks to the injector linac group for theirgreat efforts on quick recovery. The committee is glad to hear that “The major goals andtimeline to the SuperKEKB Injector Upgrade are not changed” in the conclusion.
Recommendation:
Earthquake is a natural disaster, a Force Majeure. In view of the manpower shortage inthe Linac and Storage Ring groups, the committee suggests that the management team

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look into timeline, milestones and resources, and revise the schedule accordingly.
3) Overview of the Design Issues
The design effort of SuperKEKB continued last year. Most of the effort concentrated on the
IR issues, including optics, magnets, vacuum chamber, background collimation, and collision
feedback system. These efforts have yielded a much-improved IR overall design compared
to last year. The Committee commends this effort and appreciates the good results obtainedso far. We would like to reiterate however that the IR remains the critical path item of theSuperKEKB and, as such, still requires continued or even enhanced efforts along similar lines
in the coming year. It was stated that the lattice design of IR would be finalized by the end of
March this year.
Among the changes made, the committee notes the following:•

A modest adjustment was made to the HER emittance at T=0 to relax the x-y decoupling
requirement. The HER horizontal emittance was reduced from 5.3 to 4.6 nm by installing
60% of the existing KEKB LER wigglers. The other key parameters, including thedesign luminosity, are unchanged. The remaining 40% wigglers are to be installed if theinitial complement proves useful.

•Iron yokes were added to 3 of the IR magnets to reduce the effect of leakage fields on
beams in the other ring.

•

The vertical vacuum aperture in the QC1P magnet was increased from 10 mm to 13.5 mm
to reduce the beam background.

•

Iron shields were added in the detector magnet to substantially reduce the solenoidal fieldat the beam lines.

•

The transverse solenoidal fields were also much reduced with the iron shielding. A
welcomed outcome of this is that the solenoid-induced vertical emittance growth wassignificantly reduced.

•

Synchrotron injection is now being considered for the HER to replace betatron injection
because of the limited dynamic aperture.

The committee considers these good improvements on overall SuperKEKB parameters.
Specific discussions are included in later sections of this report.
For the studies up to now, simulation studies have been used to optimize the Touschek
lifetime, aiming to reach a level of 600 seconds (when other known effects are also included,
the overall lifetime reduces to 360 seconds). The dynamic aperture limits the Touschek
lifetime, and optimizing the strengths of 52 sextupole families maximizes the momentum
aperture and the associated Touschek lifetime. The committee concurs that using the
Touschek lifetime as the figure of merit at the present stage is reasonable. However, as thedesign evolves and the Touschek lifetime goal is more firmly established, it will be necessary
to add other figures of merit to the optimization. Effects of beam-beam interaction on
luminosity with and without error effects, for example, could be another figure of merit. In
such an effort, the committee wishes to stress that attention must be paid to the additional lossof luminosity due to the interplay of multiple beam dynamics effects as observed at KEKB.
Realistic and 3D modeling of the IR optics is one key issue addressed in the past year. The
simulation tool is implemented in 3D without paraxial approximation and takes into accountthe relative tilts between the solenoid axis and the beam directions. This is good progress.
The 3D solenoid field distribution with magnets and iron shielding included is in preparation,

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and will soon be ready as part of the modeling effort.
The beam-beam interaction also has an effect on the injection background through verticalbeam blow-up. This background has not been simulated yet. It is suggested that octupoles beused to shape the phase space profile to control this effect. How and whether this can beachieved remains to be seen.
The solenoid field of the detector is well compensated except for the space between QC2RP
and QC2RE, where an additional long weak solenoid was inserted to improve thecompensation. Unfortunately, the addition of iron shielding was not possible because theiron could not be sufficiently constrained against the force of the solenoidal field. It wasnoted that after compensation, this optics complication did not affect the dynamic aperture
appreciably.
The solenoid orientation has been set to bisect the angle between the two beam lines, and isconsidered frozen because the magnet designs have already been launched. Following a
study in 2010, an equal split of the crossing angle is expected to be very close to the optimum.
More significantly, however, is the fact that after adding shielding to the solenoidal field, theexpected increases of vertical emittances due to the solenoidal field have reduced from 4 pm
to 1 pm. The choice of solenoid axis angle is no longer as critical an issue as in 2010.
Much effort was also devoted to the estimation of error tolerance and the development of
optics correction systems. The error tolerances of IR magnets tend to be very stringent. The
correction systems presently envisioned include skew quadrupole windings on each of the
sextupoles, which replace the orbit bumps at the sextupoles as used at KEKB. Chromaticity
compensation knobs include skew sextupole windings or rotating sextupoles. Designs ofthese systems and their parameters are progressing. The committee looks forward to hearing
an update on this very important topic.
An impedance budget has been developed but not presented to the committee. It is suggested
that a constantly updated impedance budget be maintained for SuperKEKB with inputs fromthe beam dynamics and the vacuum groups. In addition, a “policing function” should be
implemented to enforce the limitations imposed by the impedance budget.
A detuned lattice was presented to the committee as an example lattice for T=0 operation. In
this example, the beta functions at the IP were raised, so the natural chromaticities are about
equal to the KEKB values. It was found that injection into the LER could be achieved
without the damping ring as the dynamic aperture is quite large, and the Touschek lifetime isabout an hour. However, it is assumed in this example that the IR is already installed as
designed and is available at T=0. If this is not the case, the committee recommends
considering another T=0 backup which utilizes temporary magnets or magnets at zerostrength across the IR.
Recommendation:
Maintain an updated overall impedance budget and consider appointing a responsible
person or team (“impedance police”) to evaluate and approve impedance-wise all
items to be installed in the machine4) Overview of Construction Status
The KEKB group continues on an aggressive and determined development and construction
project for the SuperKEKB. This began with the announcement of ¥10 billion by the
Ministry of Education, Culture, Sports, Science & Technology Japan (MEXT) over three
years starting in the Japanese fiscal year 2010 (JFY2010) towards the upgrade of KEKB. The

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total construction budget is set at ¥31.4 billion with an operations budget beginning in
JFY2014 once the construction is completed before the end of JFY2014, referred to as the
T=0 milestone.
Like all aspects of KEK, the major earthquake that struck on 3 March 2011 had major
impacts on the construction of SuperKEKB. Nevertheless, the SuperKEKB team believes
that the T=0 milestone (defined as the completion of construction and commencement ofoperations) can still occur before the end of JPY2014. The damage from the earthquake wassignificant, but not catastrophic. Representative damage presented to the review committee
included damage to the D5 Power Supply Building, the LLRF area also in D5 and damage
associated with the klystrons and magnets in storage. The damage to the klystrons, wiggler
magnets that were being held in storage during construction, and the beam pipe bellows were
those with the largest machine performance concerns. The SuperKEKB Team verified thatthe wiggler magnets and the klystrons sustained no performance damage. The team has
prudently and effectively begun a radiographic examination of all of the beam pipe bellows
that will allow the detection of any damage without disassembly. Leaks and other vacuum
system damage to the linac were immediately repaired as the environmental conditions within
the tunnel severely degraded (moisture) after the earthquake. The civil construction of thetunnel (floor, walls, and ceiling) also sustained damage and as would be anticipated, the ring
became significantly misaligned. Supplemental funds have been received to address thedamage resulting from the earthquake and high power klystron tests as well as the HER
bellows radiographic examination are underway.
The T=0 milestone has not been changed, so the construction schedule has been somewhat
compressed due to delays caused by the earthquake. The SuperKEKB team has carefully
considered and prioritized the scope required for T=0. Notably, the beam current, bunchcharge at the injector and βy* have been scaled back for optimization during thecommissioning operations. The commissioning is scheduled in two phases with theagreement between SuperKEKB accelerator and Belle-II detector; Phase-I is the collider
commissioning for achieving luminosity of 1x1034 cm-2s-1 with Belle-II solenoid, and PhaseII is the commissioning with Belle-II detector and machine tuning continuing to increase
luminosity. It is recommended that a back-up commissioning plan be developed for
performing the initial commissioning without IR components.
While progress and management of the construction project is strong, the compression of the
project schedule resulting from the earthquake and slippage of some technical areas has
greatly increased the need for careful integration and “traffic planning.” Facility repairs,
additional alignments, magnet installation and larger aperture cooling piping replacement all
require almost simultaneous access to the tunnel with the current schedule. Planning ofactivities in various parts of the tunnel must be done in exquisite detail to avoid delays andinefficiencies (from multiple groups being in the same area at the same time), and loss orrepetition of progress from subsequent groups degrading or undoing work previously done.
A trivial example of what can happen if this integrated planning is not detailed enoughfollows: At the home institution of one of the reviewers, a magnet was carefully installed andprecision aligned to the few micron level only to discover a few days later the large dusty
footprint of a technician stringing cable was found on top of the magnet. Needless to say themagnet needed to be realigned.
Staff shortages remain. While staff has been added over last year, the levels are still
considerably short of the 77 FTEs needed for the complete construction phase. According todata presented at the review, total staff (permanent and non-permanent available staff) was 61
FTEs in December 2010, 66 FTEs in April 2011, and 67 FTEs projected in April 2012.

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Unfortunately, unless the acquisition of staff is accelerated the shortfall will be compounded,
as work is not completed on schedule for lack of resources. This in turn will increase theneed for more staff that will cause more work to fall behind schedule.
Recommendations:
In the face of chronic staff shortfalls, a prioritized staffing approach that applies
position slots to those areas of the highest impact is needed. Additionally, active
development of multiple creative alternative solutions to meeting staffing shortfalls
should be established.
5) Belle II Construction and Commissioning
Continuing from the KEKB success of integrated luminosity of 1 ab-1, SuperKEKB aims tointegrate a total of 50 ab-1. This will yield the possibility of a much-improved accuracy indetermining the CP violation parameters, in searching for new physics beyond the Standard
Model and possibly new particles, and to provide data to resolve mode-by-mode statistics.
To deal with the luminosity increase by a factor of 50, Belle is undergoing a substantial
upgrade of all its subsystems. The inner beryllium beam pipe radius is reduced from 1.5 cm
to 1 cm. The first pixel vertex detector layer (there are two layers of pixel detectors and four
layers of Silicon strip detectors) is 1.4 cm. The beryllium pipe is double layered with paraffincooling. An injection veto algorithm has yet to be designed. To minimize the loss of events,
an improvement of the pixel detector integration time from 20 µs to 5 µs was proposed, but isunlikely to be implemented. Other options are being pursued.
An effort has been made to estimate the expected increase of beam background. It is
expected that the main issue will be radiative Bhabha events. It was noted that there is only afactor of two in the safety margin between the background from lost particles and theradiation lifetimes of some sensitive detector components. The detector solenoid axis willbisect the crossing angle of the two beamlines. The BEAST-II assembly to be used duringcommissioning stage of SuperKEKB is also under design.
A request was made by the Belle collaboration to raise the SuperKEKB center-of-massenergy from 11.5 GeV to 12 GeV to study the charged bottomium resonance 5S states. Since
the LER (positrons) energy is limited by the BT magnets, the easiest way to raise the centerof-mass energy seems to be to raise the HER (electrons) energy by ramping up after injection.
There might be a small reduction of the peak luminosity as well as a loss of top-up mode ofoperation.
6) Dynamic aperture and IR modelingInteraction region (IR) modeling and its impact on the dynamic aperture and the Touschek
lifetime is one of the most critical ingredients in the SuperKEKB. Much progress has been
made since the last review. Introducing an iron yoke into the superconducting quadrupolessignificantly minimizes the magnetic interference between two beamlines near the interaction
point. This change also reduced the number of multipole correctors, and resulted in a
simplification of the magnet design and localized the solenoid compensation.
The solenoid field was eliminated from the beamline by introducing an iron shield. As aresult, the rotational symmetry was broken, and a more detailed three-dimensional solenoid
model was incorporated into the IR modeling. Most importantly, the optics modeling itself
was significantly improved by using a localized coordinate system centered on the design
beam axis. Fringe multipole fields from the interconnect wiring at the SC quadrupole end
were also included. This more realistic model actually led to some degradation in the
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dynamic aperture. However, after several adjustments to the magnets and optimizing thecorrection system, the degradation was completely removed.
The Committee is pleased that this achievement was largely possible because of the close
cooperation between the magnet designers and beam dynamics specialists.
The Touschek lifetime is a suitable figure-of-merit for characterization of lattices optimized
with respect to nonlinear effects. However, it is important to take account of the beam-beameffect in computing the realistic Touschek lifetime in a high-luminosity collider, including
the beam size modification caused by dynamic beta/emittance change.
Despite many improvements in the dynamic aperture and IR modeling, the resulting
Touschek lifetime remains low, approximately 600 second. Moreover, the lifetime
calculation was based on an ideal lattice without machine errors and beam-beam effects. Any
degradation could result in an overall reduction of the beam lifetime, and therefore
compromise the machine performance. The Committee would like to see a sizable increasein the margin of the Touschek lifetime.
Recommendations:Finalize the optimized dynamic aperture with the computed 3D solenoid field andimproved IR modeling, in order to provide timely input for the magnet designers to
finalize the IR lattice design.
Simulation the impact of realistically assessed field errors and alignment errors in the
final-focus magnets on the dynamic aperture, and develop a strategy for improving itby empirical tuning of the multipole correctors incorporated in the IR magnet design.
7) Error Tolerance and Optics Correction
The experience gained in the KEKB optics correction was applied to simulate the correctionof the SuperKEKB lattice; similar COD-based techniques were tried out with the aim ofminimizing the x-y coupling and beta-beat.
It was assumed that the x-y coupling was caused by rotational errors of the quadrupoles andmisalignment of the sextupoles. Ignoring all the BPM errors, the vertical emittance of thering can be reduced by a factor of 46, down to 1.5 pm, using the correction scheme.
Assuming 100 random error distribution with various BPM resolutions, the results indicatethat the BPM resolution should be better than 2 um and the BPM rotation error less than 0.3
mrad in order to correct the emittance down to around 2 pm after several iterations. This also
restores the dynamic aperture.
The optics correction of beta beating was analyzed with respect to the BPM resolution. If the
BPM resolution is better than 2 um, the beta beating will be reduced to less than 5%
horizontally and 10% vertically, as estimated from 100 random error sets of BPMs. The studyof the optics correction will continue under various conditions and follow closely the
progress of the lattice optimization. The standard correction procedures and schemes canthen be established. It is also essential to use the most up to date measurement data for themagnets, BPMs and power supplies to optimize the correction strategy.
The inclusion of realistic details, especially in the IR region, will be very important. To
complete the study, more optimization should be carried out to include more errors andcorrections. The optimal settings of the twelve families of skew-sextupole chromatic
coupling correctors need to be found.
Recommendations:Page 9 of 26

The magnet group has manufactured a prototype of the rotatable sextupole. The
detailed field measurement and mechanical precision need to be checked and the
proposed correction scheme should be evaluated using the measurement data of thisrotatable sextupole. This scheme will require much more study: how to use these
correctors, how to minimize effects on the beam aperture.
The Committee recommends carrying out a detailed simulation of the correction of
the IR lattice distortions caused by realistically assessed field and alignment errors in
the final-focus magnets.
8) IR Magnets
Work continues on all aspects of the complex systems of the Interaction Region (IR) and inparticular the magnets. The IR magnet design continues and optimization progresses. Since
the 16th KEKB Accelerator Review Committee meeting, iron yokes have been introduced
into a number of the quadrupoles and the number of leak-field correction coils has been
reduced. 3D designs of QC1 and QC2 have been completed, and their impact on beam optics
is being evaluated. The compensation solenoid is being redesigned and iterated against thebeam optics impact. Brookhaven National Laboratory (BNL) has been added as acollaborator and will fabricate the corrector and leak-field cancellation coils.
In the area of research and development, the QC1P R&D design verification model magnet
has been constructed and cold tested since the 16th KEKB Accelerator Review Committee
meeting. Vibration modeling and studies have also continued. The fabrication of a harmonic
coil for magnetic field measurements has been completed, and magnetic tests of the R&D
magnet will begin shortly. These tests will increase confidence in the design and calculationsof the magnetic design.
The two dimensional design and modeling of the magnets has been completed, and theoperating points all appear to have an adequate operating margin below the critical currents.
Calculations of the 3-dimensional solenoid fields have begun. The compensation solenoids
appear adequate, with the exception of the region where the BPM on the ESR side of the IR
precludes the use of a compensating solenoid.
BNL’s fabrication schedule of the corrector and leakage compensation coils is consistent withthose of the magnets being constructed directly under the supervision of the SuperKEKB
group.
Additional prototypes (QC1P and QC1E) are scheduled for 2012, and the complete
construction of the IR superconducting magnets is scheduled for the first part of 2015.
The schedule for the completion of the magnets by early 2015 is very aggressive and has noschedule contingency. This leads to a natural tendency to move as quickly as possible fromdesign development activities into fabrication. The consequent risk is that construction may
begin prematurely on a magnet with the potential of producing a magnet that may not meet
performance requirements. This tendency should be appropriately resisted. As wasrecommended from the previous review, a clear set of detailed milestones and decision points
should be established, with criteria based on performance requirements. This is needed forthe remaining development and fabrication of the IR SC magnets and cryostats so that
progress can be carefully tracked. In addition, a backup contingency plan should be
developed in case the IR development and fabrication strays from the milestone and decision
point plan.
The SuperKEKB team is commended for the vibration studies and mockup testing that isscheduled, and encourages all efforts are employed to ensure that these are carried toPage 10 of 26

completion and are a fully adequate set.
Overall, the IR area (both magnets and vacuum system) remains the area of highest risk forboth technical and schedule. Nevertheless, the SuperKEKB is proceeding well in this area.
Recommendations:
The committee recommends establishinging a clear set of milestones and criteriabased decision points for the development and fabrication of the IR SC magnets,
corrector and compensation coils, and cryostats so that progress can be carefully
tracked and contingent plans enacted in a timely manner if required.
9) Beam Background
Beam background is expected to become much more serious than in KEKB due to the higher
beam current, higher luminosity, and smaller IR pipe size, among other factors. The sourcesof background considered are Touschek scattering, beam-gas Coulomb scattering, radiative
Bhabha, synchrotron radiation, and the two-photon process. The beam-beam effect has not
yet been included. A collimation system distributed around the ring and especially near the IP
has been worked out based on simulation results. A collimator upstream of IP is shown to bevery effective in removing the synchrotron radiation background. Touschek background isshown to be reduced to <0.2 GHz. Radiative Bhabha is found to be the leading backgroundcontribution.
Although most radiative Bhabha loss occurs at more than ten meters from the IP, there is still
7 GHz background for HER and 6 GHz for LER within four meters of the IP. The Bhabha
gammas also generate neutrons. Additional metal shields are to be added to stop the gammas
and the neutrons. This shielding scheme remains to be designed. The two-photon processcontribution is estimated to be negligible.
A more complete simulation effort has been initiated and more results are to come. What
will be included are: 3D solenoid field, beam-beam, and the whole detector geometry.
The Committee encourages the preparation of the simulation tools as planned, and to include
beam-beam effects soon. Given the many difficult demands on the IR, as much as possible ofthe background reduction should be addressed in the ring. In addition, the Committee feelsthat there are a few questions to be addressed before the collimation system can beconsidered optimized:•

It is not clear why the beam-gas bremsstrahlung is not an issue as in many other colliders.

•

To collimate beam-gas background, a vertical collimator (the only vertical collimator in
the design) is added at ~60 m from the IP. It was estimated that this single planned
collimator uses up the entire budget for the transverse mode coupling instability. This
will need to be reviewed or re-optimized.

•

The loss factor of collimator ridge geometry calculation gives unexpected results, leading
to a particular choice of ridge design. This needs to be reconfirmed with other experts
and/or other codes.

•

In some cases, particle loss occurs in multiple turns. In those cases, it might be better toinsert collimators away from the IP to minimize secondary background. In this study,
multi-turn simulations will be needed.

•

Another way to have an overall collimation design is not to differentiate according to thebackground sources, but according to beam dynamics, i.e. horizontal betatron, verticalbetatron, and synchrotron collimations at dedicated, special-purpose locations.
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It is planned that commissioning with Beast II will enable studies of background and collision
tuning, with staged phases of increasing beam currents. The Committee feels this a good
approach10) IR Vacuum Chamber and Assembly
A new vacuum chamber layout has been presented taking into account the new insertion
magnets and the additional ion and getter pumps. The cross sections of the chambers havebeen adapted to the new aperture requirement. The chambers have tapered sections for low
impedance and to shield against synchrotron radiation. It is proposed to provide small ridges
along the wall to reduce the reflection of synchrotron radiation. The central pipe consists of adouble wall Beryllium tube brazed to Titanium end manifolds. To avoid corrosion of thisdelicate pipe with brazed joints, cooling with paraffin is required, as was presented to the lastcommittee meeting. The tapered connections adjacent to the cryostats will be made out of
Tantalum to provide shielding. These chambers will have ducts for water cooling and gold
coating on the inside surface. The proposed design relies critically on reliable, UHVcompatible joining techniques between these different materials: brazing, hot isostaticpressing and manufacturing of Tantalum chambers. The joining techniques require validationof each of these steps.
For the connection of the IP chamber to the cryostat, it is proposed to use radiation hardelastomer seals. In this way, the insulation vacuum and beam vacuum are independent, which
is very important requirement.
The revised vacuum layout has been improved with the addition of ion pumps and getterpumps located outside of the cryostat at a distance of roughly ±4m from the IP. Since
photon induced desorption dominates the gas load, a dynamic pressure of 10-5 Pa can be
expected at the IP. However, this pressure assumes an optimistic photon desorption
coefficient of 10-6 molecules/photon.
To achieve such a low eta value it is proposed to use a gold coating. Measurements for acopper sample obtained in a test at the Photon Factory were shown to the committee. A
subsequent test with a gold sample is planned.
A mock-up is proposed to evaluate in detail the assembly and installation procedures of the
IP chamber and the SVD. The committee considers this as a vital step, which must precede
the final design and the manufacturing of the IP components including magnets and supports.
Recommendation:
Validate design choices, the assembly and installation procedures.
Confirm parameters for the pressure estimates.
11) Collision Feedback
Based on KEKB data, the vibration magnitude of the final quadrupoles and the resulting
beam orbit motion could be a few times the vertical beam size in SuperKEKB.
The problem is addressed by four measures: using the coherency of the ground motion,
modified magnet supports, additional damping of oscillations, and finally orbit feedback.
A modal analysis has been performed with the ANSYS code. Vertical oscillation frequencies
appear around 26, 36, and 53 Hz.
When evaluating the effect on the beam-beam separation, the vibration coherence of bothbeams must be taken into account. The measured coherence of the ground motion between
the IR quadrupoles for the magnets of both beams reduces the relative motion of the two
Page 12 of 26

beams by a factor 10-20. The cancellation uses the fact that the fractional tunes for the tworings are about the same. It was remarked that at KEKB, vibrations on the left and right sideof the collision point had been absolutely uncorrelated.
For SuperKEKB the quadrupole oscillations will have smaller amplitude and be at a higher
frequency thanks to improved supports. The dominant remaining oscillation frequency is dueto the 3 Hz component of the ground motion. A 50% reduction of motion at this frequency
will be achieved by adding damping material. The lever arm effect has been included in thecalculations.
Evidence from KEKB supports the assumption that ground motion is the dominant source of
quadrupole and beam motion and that vibration from 4.5-K helium cooling, water-cooling,vacuum pumps (no mechanical motion) can be neglected. Namely, a model based on groundmotion and mechanical resonances makes predictions that are consistent with themeasurements at KEKB. No other sources of vibration were considered.
The horizontal orbit feedback cannot use the beam-beam deflection method, since the beambeam parameter is low and there are two sources of the horizontal beam-beam kick. Instead adithering system like at PEP-II is foreseen. The expected high ZDLM rate will allow goodprecision and fast response.
K. Ohmi has simulated the dependence of the luminosity on the horizontal beam-beamseparation. The luminosity drops rapidly for a separation larger than 5-10 micron (roughly thehorizontal rms beam size). The horizontal collision feedback system need not be very fast,
since the most important perturbation is expected to be rather slow, around 3 Hz.
A proportional-integral-derivative controller proposed for the feedback will not have any gain
above the first resonance of the system. Therefore, while it might be able to reduce thedisturbance at 3 Hz, as planned, it will either be inactive or may even amplify motion for thehigher-frequency resonances at 26, 36 Hz, 53 Hz, etc.
Helium pressure oscillations at 4.5 K could excite quadrupole vibrations around 10 Hz
Other possible concerns are vibrations of the magnet cold mass inside the cryostat anddifferential oscillation modes of the support and cryostat (if any) that would move theelectron and positron quadrupole in opposite direction. A question is whether the oscillation
damping might also lead to a decoupling from the ground at relevant frequencies, which
could degrade the coherence of the magnet motion.
High current beam operation and the associated heating effects could lead to movements ofaccelerator beam-pipe components, changes in BPM readings, and to additional beam motion.
How does the speed of the horizontal collision feedback compare with the speed of the global
orbit feedback? Is there a possible cross talk?
Recommendation:
Continuous attention should be paid to minimizing IR magnet vibration. Any
additional sources of mechanical excitation in the IR region, e.g. from the experiment,
should be avoided as much as possible, and their magnitudes carefully checked.
Actual quadrupole vibrations inside the cryostat should be measured on the first IR
magnet prototypes, e.g. by geophones or laser system, and compared with model
predictions.
The committee repeats its previous recommendation to look at more sophisticatedfeedback techniques, e.g. using state space formalism.

Page 13 of 26

12) Magnet and Magnet Power Supply System
The KEKB Group continues to do a considerable amount of consistently high quality work in
the area of the ring magnets and magnet power supplies. As would be expected after the
March 3, 2011 earthquake, a major fraction of the activities in this area was assessing andmitigating damage and ensuring that the stability of the tunnel complex is assured. The
alignment and stability of the magnets and the rings depend completely on this assurance.
The earthquake created considerable damage in the tunnel area with large movements andchanges in alignment being observed, particularly on either side of expansion joints. This is
not surprising as the expansion joints completely decouple the adjacent concrete structures sothat they will move independently of each other in the event of an earthquake. This createdvery large misalignments where the beams and magnets crossed these expansion joints. The
locations of all the expansion joints are easily seen when looking at the post-earthquakealignment measurements.
Several types of earthquake-related damage occurred within the tunnel complex, including:cracking of platforms and concrete structures, liquefaction in places, surface soil disruption
cracks, floor movement, cracks (both structural and superficial), and large shifts in magnet
and equipment stands. The KEKB Magnet group is instrumenting the tunnel with acomprehensive GPS network as well as monitoring potential shifts between expansion joints
and performing extensive soil surveys. All of this is to establish and understand if residual
stresses have been created by the earthquake that will be released (slowly most likely) overtime and degrade alignment.
Fortunately, although some of the wiggler magnets sustained damage, it has been determinedthrough magnetic measurements that all of the damage was superficial and had no impact onmagnetic performance. Unfortunately, the same cannot be said of the KEKB LER dipoles.
Many of these dipoles were damaged to the point of being unusable, but it is estimated that
10-15 of these magnets are still serviceable, which is a sufficient number for SuperKEKB.
This will be verified by magnetic measurements later this year.
A creative approach to supplying additional corrector coil windings to the magnets without
disassembly has been developed, but it includes a significant number of electricalconnections (three per turn), so that care much be exercised to ensure the final installation iscorrect and robust.
The environmental conditions could no longer be controlled in the tunnel after the earthquake,and the temperature is approximately five degrees below the nominal operating temperature
at the time of this review. If the environment of the tunnel remains uncontrolled, thetemperature will continue to drop until it reaches the ambient temperature of the groundsurrounding the tunnel. So long as the temperature remains uncontrolled, precision alignmentof the magnets upon installation is futile. The approach to installation and alignment should
either be amended to incorporate the need for a complete final precision alignment once theenvironmental controls and temperature stability of the tunnel are reestablished, or theenvironmental and temperature control of the tunnel should be reestablished prior tosignificant magnet installation. Note however that until the long-term stability of the tunnel
complex is documented, neither the environmental temperature controls, nor precisionalignment is advisable.
As is planned, careful active monitoring of shifts across expansion joints must continue forthe foreseeable future (throughout all the construction, commissioning and operation ofSuperKEKB). Without such active careful monitoring delicate structures such as the RF
bellows will remain at risk.
Page 14 of 26

Little time was spent describing the progress on the accuracy of the mechanically rotating
sextupoles. There was an almost parenthetical mention that maintaining the magnetic center
during a rotation was an issue, but no discussion of was made during the review. The
committee anticipates seeing a full discussion of these important developmental magnets atthe next review.
The magnet power supply systems seems to be well in hand and understood. A creative
approach to providing 24-bit (0.06 PPM) digital control was presented, but the committee
remains cautious. Although 1 least significant bit (LSB) resolution was shown, long term
stability with feedback was demonstrated to only 1.4 PPM / 8hrs, a factor of 23.5 times larger
than the resolution.
Recommendations:
Once the long term stability of the tunnel complex has been documented, either
reestablish environmental temperature control of the tunnel complex to allow precisionalignment to proceed along with magnet reinstallation, or amend the approach on magnet
installation so that only rough alignment without permanent anchoring is done until
temperature control and stability are reestablished when a final complete precisionalignment may be performed.
13) Beam diagnostics, Feedback systems
The KEK team has great skills in beam instrumentation and the application of various
techniques to the several orbit measurement and feedback projects. Very solid progress has
been achieved in the design and development of beam diagnostics and feedback systems forSuperKEKB with effective use of existed KEKB diagnostics and feedback systems as wellapplying the technical expertise. We appreciate the work in defining the Bunch-by-Bunch
current monitor and presenting it at this Review.
With the low cut off frequency in LER beam vacuum chamber, 509 MHz-based systems arebeing developed. The development of boards and detectors is in very good shape, including
1) Digitex 17K94A 509 MHz detector, 2) turn-by-turn monitor, 3) IR feedback detector with
uTCA board and feedback processor, 4) bunch position detector and feedback digital filter(iGp12), and 5) bunch current monitor. The TBF and LBF are considered for LER and HERof SuperKEKB, but LBF is only an option for HER. The DAFNE type longitudinal kicker isbeing adopted, and the related experiments are being made under the collaboration withSLAC and INFN-LNF. The optics issues have been examined, including tunes, phaseadvance feedback monitor and kicker, phase advance between collision point and feedback
detector, phase advance from injection point.
There has been significant technical work on the 509 MHz heterodyned BPM processing
system for the LER, with a plan to produce final modules in the next year. The plan for the
HER uses the existing 1 GHz modules from KEKB (the VXI modules developed by HP). In
the 2010 review, we wondered if long-term support for the HP BPM modules might become
problematic, and if it was worth investigating a variant of the new 509 MHz LER module,(basically a different LO to mix the signal into the processing channel). We respect the needto balance manpower among projects, but again wonder if this path has been investigated (orrejected for good reasons), or if the issue of how to support the original KEKB HP BPM
modules is essentially deferred to a later date. The time to do this is before the mass
production run.
The year has shown technical progress for the gated turn-by-turn monitor, and the final
technical choices are being made in conjunction with the optics group as well as a plan forPage 15 of 26

the number and location of the BPM monitors. The slides mention the evaluation of yet athird BPM electronics package, based on the commercial Libera system. We suggest thatchoosing among the possible options would be easier if there was some more specificfunctional requirement (isolation, or dynamic range, etc.), so that a decision could be made if
the gated implementation is adequate as designed or if alternatives must be developed orpurchased.
The plan to control coupled-bunch instabilities in transverse and longitudinal planes is welldefined, and the KEK team has very important expertise and experience. The issue of
feedback control for tunes very near the ½ integer was explored last year. The possible
solutions include use of two independent BPM pickups, roughly 90 degrees apart in betatronphase, followed by two feedback processor systems, each with independent kickers. Thisapproach certainly has flexibility, and offers increased gain, though it doubles the installed
hardware.
We repeat our advice from the last review to plan now for high-current heating of the beamline components, and to develop beam line interlocks and monitors for the kickers, amplifiers,
kicker loads, connections, etc. in the transverse and longitudinal systems.
The design of the IP orbit feedback processor was presented including a detector with CIC
signal processing in the signal chain. A special “uTCA orbit feedback processor”
architecture was shown. We understand the intent is to use Matlab/Simulink tools to develop
a control filter to run on this platform. This is an excellent general-purpose approach.
However, we repeat some of our concerns from last year, particularly the important need totie the modeling of the magnet motion, dynamics of the magnet system and the actuator
responses, etc. into some sort of feedback model.
Recommendation:
Define a technical specification for the necessary performance of the gated monitor
system, so that a clear decision can be made comparing the proposed gating techniqueand the commercial medium band detector.
The orbit feedback instrumentation effort should be coupled with the modeling effort
that has been presented under the heading “Collision Feedback”. The design andscale of the feedback controller, and algorithm, should be very tightly coupled toknowledge of the system dynamics. It is a very complex system and the necessary
task will advance the state of the art in accelerator control.
14) Photon Monitors
Three different kinds of photon monitors are foreseen: a synchrotron radiation monitor for thelongitudinal bunch length (using a streak camera) and horizontal beam size (using aninterferometer); an X-ray monitor for the vertical beam size; and a large angle beamstrahlung
monitor for beam-size matching and IP tuning.
The photon monitors for the damping ring were covered in a separate presentation.
The heat deformation of SR mirror was already a big problem at KEKB. For SuperKEKB a
new mirror is being developed which addresses this problem; a quasi monocrystalline
diamond mirror is being produced together with a Japanese Company, Seki Technotron,
where 3-4 monocrystals are joined together. The new design should have a much improved
surface smoothness as well as excellent heat conduction and low thermal expansion
coefficient. The SRM interferometer to be used for the horizontal beam size measurements
cannot do single shot measurements. Applying it to the vertical beam size will yield only
Page 16 of 26

marginal resolution.
The X-ray monitor uses a coded aperture imaging technique that has been successfully tested
at CesrTA. The scatter measured at CesrTA agrees well with simulations, demonstrating thatthe result is statistics limited. There is a plan to improve the associated detector and further
reduce the error in the measured beam size by raising the photon detection efficiency at
higher x-ray energies. Both Si+Au and Diamond+Au masks have been fabricated and arebeing tested at CesrTA. A 64-channel digitizer and readout system for the XRM will betested at ATF2. The ultimate goal is to resolve the beam size for head and tail separately,
which might allow a direct monitoring of the head-tail and e-cloud instabilities; the minimum
goal is to resolve the beam size of all the bunches shot by shot.
A third photon monitor is planned for the beamstrahlung from the collision point.
Beamstrahlung monitors were very successful at SLC, and were used for several years todetect which of the two colliding beams was responsible for performance degradation. The(different) more advanced LABM planned for SuperKEKB is based on the papers ofBonvicini. A first very short test had been done in the last days of CESR operation, with only
one side of the IP operating. The polarization of the beamstrahlung radiation at specificazimuthal points varies depending on the beam-size mismatch, offset or rotation of one beam
against the other. The LABM comprises 4 narrow acceptance telescopes using light extractedwith small beryllium extraction mirror, counting photons in two polarizations and four bands.
An optics channel prototype has been built, but changes to the recently added IR shielding
may be needed. Production of the optics box with light collectors has started, and a possible
beam test at Frascati in 2013 is being considered.
The committee is pleased to see that the SRM and XRM are on track to be ready at the timeof the SuperKEKB start up with beam, the LABM will be ready soon after as required by thecommissioning plan.
One remaining question is at which luminosity levels the LABM starts to become useful.
Another question is the difference between the beamstrahlung, which has been examined andthe coherent bremsstrahlung that has been predicted for other storage-ring colliders.
Assuming that the effective horizontal beam size is σz θc/2 the SuperKEKB parameters
would appear to be close to the coherent bremsstrahlung regime.
15) Development of New LLRF System
The committee finds good progress on the development of the new digital LLRF system,
consisting of µTCA-based FPGA boards and PLC. The new LLRF system prototype has beendeveloped and evaluated with measurable improvement. Prototype boards are in hand andbeing tested using a dummy cavity. Initial results show that the amplitude and phase stability
meets the requirements but the long-term thermal drift is out of specification. The systemstability should be confirmed by external “outside the loop” measurements on the test system.
The thermal drift is mainly coming from the front-end band-pass filter and is being addressedby compensating locally with thermally sensitive components. It is expected that a revisedboard will be tested soon. The timing distribution for the new system will be via phasestabilized optical fibers. This is expected to give excellent timing stability over long
distances. The existing timing distribution system will be preserved as a back up.
Recommendations:
Demonstrate acceptable thermal stability with the revised boards.
Confirm the system performance with "out of the loop" measurements.

Page 17 of 26

16) Improvement of Superconducting Cavities
The existing SCRF systems were relatively unharmed by the earthquake. The high power
klystrons retained vacuum but they have not yet been tested. Ancillary components sufferedsome damage and misalignment but recovery has been effective and timely. If fully recovered
the present inventory of cavities and RF systems is adequate for T=0 commissioning. As was
known before the earthquake, some reconditioning of cavities and redistribution between therings will be necessary to reach full current. Analysis shows that the HOM load power in the
SRF cavities is significantly higher at the higher current and shorter bunches in the newmachine. According to simulations the current HOM damper might overheat to 190 C. A
new HOM damper was fabricated and tested with an improved cooling scheme and reduced
thickness of the ferrite plate (4mm to 3 mm). Unfortunately, it failed at the higher power
level. While the existing stock of cavities and loads is thought to be adequate for T=0, thecommittee recommends continuing the development of a robust high power load as a backup,
possibly using silicon carbide. Ideally this should be developed and tested in time to allow a
possible retrofit to the existing cavities before high current beam operation is needed.
A horizontal high-pressure-rinsing (HHPR) system has been developed and demonstrated
very successfully on a single cell cavity, without a cryomodule. The target of this test is torestore the performance of the SRF module after many years of operation or accidental
contamination without taking apart the whole cryomodule. While this approach has somerisk, it would be highly attractive to avoid the time necessary to fully rework the cryomodules.
The committee recommends trying this on a spare cryostat as soon as possible while
recognizing the risk that the module could be degraded or lost.
Recommendations:
Demonstrate improvement of the cavity performance with the horizontal highpressure rinsing system.
Prepare and test the higher power HOM load as soon as possible.
17) Cavity for Damping Ring
The damping ring RF system has progressed well since the last review. Work has been doneon the shielded, welded interconnect between the cavities to show that it should have a low
impedance with no trapped modes. The cavity HOM loads have been redesigned with asingle row of SiC tiles. The match is improved and the HOMs are better damped. Powerhandling should be more than adequate for the low beam current in the damping ring. The
same HOM tiles are applied to the beam pipe loads between the cavities; however they are
now mounted in the beam pipe rather than in the “wings” of the fluted pipe. While the loss
parameter of this structure may be higher than before, it is expected to be small compared to
the CSR wake. A prototype damping ring cavity is expected to be power tested in the next
few months. It is expected to meet all requirements since it is closely based on the ARES
cavity. While the committee’s recommendations from the last review were not followed,
good progress has nevertheless been made and the system is likely to be successful.
Recommendations:
Complete the damping ring cavity system test up to the full power of 180 kW withrepresentative HOM loads attached.
Verify that the loss parameter of the beam pipe SiC loads is acceptably small.
18) Production status of Vacuum components

Page 18 of 26

The committee is pleased to hear that series production of main components for the vacuum
system is in full swing this year. The first chambers produced by INP have been delivered
recently. Other components have entered the mass production phase in several Japanesecompanies or are ready to be ordered this year. Generally, all components for the HER andLER are well on schedule. NEG strips and heaters will be delivered this year and can beassembled in the vacuum chambers.
As the products are delivered to KEK, the upcoming work will concern testing andinstallation of the vacuum elements in the tunnel. A detailed program for vacuum testing andbaking of the vacuum chambers will be required to guarantee the quality assurance for thecomponents prior to assembly and installation in the tunnel.
Progress with the design of the movable mask was reported, but no final solution for themask has been found. The choice of the most appropriate material still remains under study.
The ideal material should withstand a large temperature increase without loss of mechanicalproperties or melting.
Installation of vacuum components, chambers and bellows in the magnets should be carefully
prepared to avoid interference with the work on magnets and upgrading of the water coolingsystem.
The importance of a close follow up of production in industry should be recognised. The
associated additional cost will be a good investment.
The final assembly of vacuum components with pumps, electric feed-throughs and theinsertion of the NEG strips into the chambers will require a heavy work program to beorganised on site.
A Quality Assurance program must be implemented for leak checking, bakeout, TiN coating
and backfilling of the chambers with clean, dry nitrogen. Cleanliness must be guaranteedfrom the time of initial conditioning until installation in magnets and the machine start up. In
particular, contamination of the TiN surface with water could destroy its performance.
It has become a good practice to establish individual ‘travellers’ for each vacuum element sothat its history is recorded.
Congratulations from the committee for the remarkable progress since the last meeting.
19)

Baking and TiN coating equipment

The large number of vacuum chambers which go into the HER and LER rings will require an
extensive conditioning program. All vacuum chambers will be baked and will undergo a
final vacuum validation stage. In addition, the chambers for the LER will receive a TiN
coating to mitigate the electron cloud. To cope with the large number of chambers (some 180
for the HER and 1000 for the LER), it is proposed to use hot air ovens instead of theconventional baking method with heating jackets. The required baking temperature of 150 C
can be achieved in a short time. For the TiN coating process, a special facility is planned,
which can accommodate several chambers at a time. Vertical installation as well as ahorizontal coating facility will be provided. The planning presented to the committee showsthat the installation schedule can be met.
Since the baking and TiN coating will be an integral part of the vacuum conditioning, it is
proposed that the final vacuum, including the residual gas composition, should be recordedon the traveller of each chamber.
20) RF Gun and Low Emittance Transport
Page 19 of 26

The RF gun is very challenging. The goal of 5 nC at 10 um is beyond what has beenpreviously demonstrated. Two new designs are being pursued, a disk and washer structure
and a new Quasi-Travelling Wave (QTW). Both look promising, while keeping surface fields
below 100MV/m. The QTW offers the potential of higher accelerating gradient after the firstcell, and stronger RF focusing leading to smaller beam size while preserving good emittance.
Both options used a shaped cathode and re-entrant geometry in the first cell to yield goodinitial emittance. It is proposed to use a demountable LaB6 cathode in the QTW. While thismaterial is commonly used for thermionic guns, it also looks promising as a photocathode.
The committee recommends demonstrating these new technologies in a well-instrumented
beam test as soon as possible. Ideally, both options should be thoroughly tested before adown select is necessary. Simulations show that the low emittance out of the gun can betransported and accelerated in the linac. CSR in the first arc was mentioned but not
quantified. Hopefully it is not a big effect as the energy is already high. An X-band
deflecting cavity system is being built in collaboration with SLAC to be used for slice
emittance measurements. The lasers for these guns are also challenging and must work
consistently with very high reliability in top-off mode. The committee notes good progresson all these topics.
Following the recommendations of the previous Committee, many emittance preservation
measures are being pursued: improvement of the linac alignment system using the laser
tracker is underway with the aim to achieve a sub-millimeter accuracy; stripline BPMs with
upgraded electronics have already achieved 20 µm precision in H/V beam position
measurement (<10 um being the target); and in cooperation with SLAC, a 15 MV transverse
RF deflection system will be used for transverse emittance measurement, and will be capableof reducing the transverse projected emittance by compensating for the bunch tilt caused bytransverse wakes. The Committee is satisfied with the presented schedule of system upgrade.
Recommendation:
Aggressively pursue a demonstration of the QTW gun with LaB6 cathode and the fullpower laser.
21) Positron Source
SuperKEKB requires a 50-fold increase in luminosity through higher current and lower
emittance, requiring an upgrade to the positron source. The existing electron beam of 3.5
GeV with 2 x 10 nC is used to produce positrons with two bunches of 4 nC each. For
efficient positron capture, a Flux Concentrator (FLC) and Large Aperture S-band (LAS)
sections are adopted. A damping ring (DR) is required for emittance reduction before
injecting into the LER.
For SuperKEKB, the e+ target is moved to a location further upstream to have enough margin
for damping ring injection. The e+ source upgrade contains many ingredients: target,
matching device, capture accelerating structure, capture DC solenoid, beam line, quadrupole
focusing system, damping ring, and transport lines with bunch and energy compression.
Two types of flux concentrators (FCs) have been developed; one in collaboration with BINP
and the other with SLAC and IHEP Beijing. The BINP device suffered from a breakdown
problem above 7 T field level in 2011. The earthquake interrupted work on this device, andthe damaged flux concentrator was sent to BINP for repair. The flux concentrator of the
SLAC type will be used for T=0 and for the earlier linac commissioning (which will startalready next autumn). Special hardened copper will be used for this FC in order to shift themechanical resonance frequency away from 50 Hz. A possible performance improvement by
shape modification of the FC is being explored through simulation studies. More time isPage 20 of 26

needed for R&D on the later FC upgrade. A SC solenoid is another candidate means to boost
the positron yield in the longer-term future.
For SuperKEKB the target needs to be optimized for the flux concentrator and, therefore its
design will be different from the KEKB target. An amorphous tungsten target will be used at
T=0.
The electron beam for the HER is on-axis, and the electron beam to the positron target passes
through an offset bypass hole.
The SuperKEKB capture section will use a mixture of L-band and large-aperture S-band(LAS) structures. This combination represents a good compromise. By re-using existing Sband components it reduces the initial cost compared with a pure L-band system and provides
comparable or even better performance. A large aperture S-band structure is chosen for its
acceptance. The frequency difference between S band and L band structures sweeps out
satellite bunches, which would otherwise be critical for the damping ring radiation shielding
The first L-band klystron tube and the first L-band structure were delivered in March 2010,
and an L-band operation test stand will start in April 2012. A built-in collinear power loadusing Kanthal (deposited by atmospheric plasma spraying) as an RF absorber avoids the needfor an output coupler and provides space for compact solenoids.
Beam optics design and tracking simulations have made a lot of progress. The fields of boththe capture section flux concentrator and the solenoid peak at 6 T. Gaps for waveguides leadto oscillations in the longitudinal magnetic field that dilute the positron transverse
emittance. Compensation of the field dips in the waveguide regions by adding hugesolenoids is being considered.
Detailed particle simulations of the positron transport have been performed from the capture
section through the linac sectors 1-2, LTR, DR, RTL, linac sectors 3-5 and BT line. A
deceleration phase mode is preferred in the capture section, since this reduces the high-energy
tail. An e- stopper is installed to catch low-energy electrons coming from the target.
A challenge is developing e+/e- compatible optics in linac sectors 3-5. Most DC quadrupolesin this part will be replaced by pulsed magnets for better matching of the three types ofparticle beams (including electrons for the Photon Factory).
Promising tracking results have also been obtained for the ECS and BCS systems in the LTR
and RTL, respectively.
The positron-injector schedule is tight, with linac positron commissioning starting early in thefall of 2013.
The design charge from the positron complex is 4 nC per bunch. The ideal design without
errors promises 6 nC, but degradation due to the waveguide gaps etc. leads to a reduction in
the available positron charge by almost a factor of two. At T=0, only 1 nC per bunch is
required, and the damping ring will not be needed due to the relaxed beta* in the collider
rings.
New shielding in the linac is required due to the relocation of the target. Initially the newly
added shielding will be more compact, facilitating the exchange of components whenrequired. This compact shielding will later be replaced by a heavier shielding structure.
Recommendations:
CSR effects in the bunch compressor should be examined.
A protection scheme for the target should be developed at least conceptually.
Page 21 of 26

22) CSR in Damping Ring
Since the last review, significant progress has been made in understanding the effects ofcoherent synchrotron radiation (CSR) in the damping ring.
The discrepancy between the codes for calculating the CSR wakefield developed by Gennady
Stupakov and Katsunobu Oide was successfully resolved. Both codes deal with realistic
vacuum chamber geometry and numerically compute the CSR wake generated by bending
magnets, including the transient effects. Currently, Oide's code was used to calculate the
one-turn integrated wake for the damping ring.
The peak value of the CSR wake is about a factor of 100 larger than the combined wake fromall other common sources. A detailed study of seven different shapes of vacuum chambers
was carried out using multi-particle simulations. Clearly, the chambers with narrower verticalgaps have a smaller wake. The well-known shielding effects of the metal chamber can
explain this result. The simulation also showed that, given the same vertical gap, theantechamber made little difference. Since the antechamber is necessary to control theelectron cloud, a vacuum chamber with a narrower gap and with an antechamber is a natural
choice for the design.
The simulation clearly displayed the difficulty in achieving numerical convergence in therefinement of the mesh used in the particle-in-cell method. The poor convergence may resultin some numerical artifacts, especially for a current that is significantly higher than thethreshold of the microwave instability. In other words, the result at 8 nC has much higher
uncertainty than the one at 4 nC.
Since two bunches with the 4 nC charge per bunch in the damping ring is sufficient tomaintain the design current through top-up injection with an injection efficiency of 60% for
300 second LER total lifetime, basing the decision of the chamber geometry on the 4 nC
charge should be a primary consideration.
However, given the nature of the narrow resonances in the CSR impedance, two bunches may
affect each other and result in a lower threshold of the microwave instability. This multibunch effect should be included in the simulation.
Recommendations:
Since there are some uncertainties seen in the simulation, the Committee recommends
that the results of this study be compared with a simulation using a Vlasov-FokkerPlanck code using the same wakefield.
Consider using parallel computing for improving the accuracy and achieving thenumerical convergence for wake calculation and particle simulation.
23) Synchrotron Injection
Synchrotron injection was presented as an alternative solution to the conventional betatron
injection scheme in the HER. The scheme seems feasible with a dispersion of -1.6 meter at
the injection point and a very thin effective septum width of 3.5 mm (compared to 5 mm in
KEKB). A preliminary design of the septum was presented. Further study of theimplications of the thinner width is necessary, along with a realistic and achievable set of
injection and stored beam parameters.
24) Beam Abort System
The beam abort system forms a critical part of the machine protection system forSuperKEKB. There are several technical and practical risks that the SuperKEKB team isPage 22 of 26

addressing. The beam abort system consists of nine principal components on both the LER
and HER:
1.
2.
3.
4.
5.
6.
7.
8.

Horizontal Kicker
Vertical Kicker
Pulsed Quadrupole
Lambertson Septum
Power Supplies
Pulse Compression
Beam Dump
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 perturbing the back of the bunch train when theabort is triggered. This requirement is necessary in order to avoid damaging the machine or
disrupting the RF system. The requirement of a rapid rise time results in a practical limit of
one power supply for each ring. There is a need to spread the beam as much as possible inorder to reduce the energy density deposition.
The tests and research development on the extraction window have indicated that, contrary to
the initial lowest order modeling, the temperature rise (equated with potential damage to thewindow) should be independent of thickness. This has been shown not to be the caseexperimentally, but the BAS team has a plausible explanation for the dependence on the
thickness. There is an indication in what the group has examined that there may be an
optimum thickness for the Titanium-alloy window that is a trade-off between two different
damage mechanisms.
The team is encouraged to examine the possibility of using two sextuple magnets instead ofpulsed magnets to enlarge the horizontal beam size at the extraction window.
A pulsed magnet with a rise time of <200 ns presents several technical challenges of which
the group appears to be well aware and is addressing. A water-cooled ceramic chambercoated with 6um thickness of Ti has been developed; the pulsed magnet has been prototyped;
and the magnetic fields were measured with and without the chamber. The measured risetime of less than 200ns is an encouraging result that shows the potential of the optimizationof the inner Ti coating thickness of the ceramic chamber. As their present prototype system
has no demonstrated margin (the effective magnetic field rise time = 200 ns), the group is
actively looking to optimize the thickness of the Titanium coating of the ceramic beam pipeand other aspects of the integrated system.
In all of the areas, there appears to be a good balance between analytical and empiricaldevelopment of all of the components of the beam abort system. Although the group has agood hypothesis for the mechanisms responsible for the window damage, there is a strong
desire on the part of the group to fully understand and characterize the mechanism.
The group is also considering alternative approaches, such as the use of two sextupoles inplace of the pulsed magnets in order to increase the spreading of the aborted beam.
A practical issue and risk is the loss of the supplier for the ferrite cores necessary for the
beam abort system.
Recommendations:
Study of a “striped” coating on the ceramic chamber or a slot type kicker is
encouraged to generate this pulsed magnet field with fast rise time less than 200ns.

Page 23 of 2625) Control and Timing System
The control system is based on EPICS and is in an extremely mature state. The KEKB teamhas profited from the EPICS collaboration and is now in the process of augmenting EPICS by
putting IOCs in every piece of hardware, effectively simplifying the connects. In addition,
the scripting languages that have been used at KEKB are now being increased to give added
flexibility. The committee fully endorses this approach.
The team is now working on adding fast, global, synchronous controls via an event driver andreceivers. This will greatly facilitate the complex timing that will be needed to control threedifferent beams through the injector chain.
Other upgrades are going on throughout the system, and the Committee is confident that theapproaches taken will lead to an excellent system. The only additional feature that seems tobe missing is the addition of ring buffers to the BPMs and other signals to facilitate diagnosis
of a complex problem by looking at the machine status immediately prior to the problem. It issuggested that this functionality be added to the control system.

Page 24 of 26

Appendix A
KEKB Accelerator Review Members
Andrew Hutton, ChairJLab

Yunhai Cai

SLAC (replacing John Seeman)

Alexander Chao

SLAC

Oswald Gröbner

CERN (retired)John Fox

SLAC (attended via EVO)

Stuart Henderson

FNAL (unable to attend)

Gwo-Huei Luo

NSRRC

Won Namkung

POSTECH

Evgeny Perevedentsev

BINP

David Rice

Cornell University (unable to attend)

Bob Rimmer

JLab

Kem Robinson

LBNL

John T. Seeman

SLAC (unable to attend)

Zhao Zhentang

SINAP

Frank Zimmermann

CERN

Katsunobu Oide

KEK, Ex Officio Member

Kazunori Akai

KEK, Secretary, Accelerator

Atsushi Enomoto

KEK, Secretary, Accelerator

Haruyo Koiso

KEK, Secretary, Accelerator

Page 25 of 26

Appendix B
Agenda of the 17th KEKB Accelerator Review Committee
17th KEKB accelerator review
Monday 20 February 2012
09:00 - 09:40

Recovery of Linac after the Earthquake

Atsushi Enomoto

09:40 - 09:55

Overview of Design Issues

Haruyo Koiso

09:55 - 10:35

Overview of Construction Status

Kazunori Akai

10:55 - 11:25

Belle II Construction and Commissioning

Karim Trabersi

11:25 - 11:55

Dynamic aperture and IR modeling

Akio Morita

11:55 - 12:25

Error Tolerance and Optics Correction

Hiroshi Sugimoto

14:00 - 14:45

IR Magnets

Norihito Ohuchi

14:45 - 15:25

Beam Background

Hiroyuki Nakayama

15:45 - 16:15

IR Vacuum Chamber and Assembly

Ken-ichi Kanazawa

16:15 - 16:45

Collision Feedback

Yoshihiro Funakoshi

16:45 - 17:30

MagnetH. Iinuma, T. Oki

Tuesday 21 February 201208:30 - 09:00

KEK Roadmap

Fumihiko Takasaki

09:00 - 09:25

Beam diagnostics, Feedback systems

Makoto Tobiyama

09:25 - 09:50

Photon Monitors

John Flanagan

09:50 - 10:05

Development of New LLRF System

Tetsuya Kobayashi

10:25 - 10:40

Improvement of Superconducting Cavities

Yoshiyuki Morita

10:40 - 11:00

Cavity for Damping Ring

Tetsuo Abe

11:00 - 11:25

Production Status of Vacuum Components

Yusuke Suetsugu

11:25 - 11:50

Baking equipment and coating equipment

Kyo Shibata

13:00 - 13:40

RF Gun and Low Emittance Transport

Mitsuhiro Yoshida

13:40 - 14:20

Positron Source

Takuya Kamitani

14:20 - 14:45

CSR in Damping Ring

Hitomi Ikeda

15:05 - 15:20

Synchrotron Injection

Takashi Mori

15:20 - 15:45

Beam Abort System

Toshihiro Mimashi

15:45 - 16:15

Control and Timing System

Kazuro Furukawa

Page 26 of 26