Report of the
Accelerator Technical Advisory Committee for the
JAERI-KEK Joint Project

May 21-23, 2002
KEK
Tsukuba, Japan

Table of Contents
Page

Executive Summary ......................................................................................1

1

Introduction ........................................................................................52

Findings and Recommendations

3

2.1

200 MeV Linac...........................................................................6

2.2

3 GeV Synchrotron .....................................................................92.3

50 GeV Synchrotron ................................................................. 12

2.4

Control Systems........................................................................ 16

2.5

Beams Dynamics....................................................................... 18

Appendices3.1

Meeting Agenda........................................................................ 22

EXECUTIVE SUMMARY
The Accelerator Technical Advisory Committee (ATAC) for the JAERI-KEK Joint Project (JKJ)
held its first meeting over the period May 21-23, 2002 at the KEK laboratory in Tsukuba, Japan.
The JKJ Project combines aspects of the previously proposed Japanese Hadron Facility by KEK
and the Neutron Science Project by JAERI. The new project is being undertaken jointly by KEK and
JAERI and will be constructed at the JAERI site in Tokai. The project is now approved with abudget of 133.5 billion yen for Phase 1. Construction was initiated in 2001 and Phase 1 is scheduled
for completion in 2006. Phase 2 carries an additional 55.5 billion yen and is not yet approved forconstruction. The committee also notes that the JKJ Project will provide Japan with a preeminent
facility in high energy, nuclear, and materials sciences.
The ATAC heard presentations concerned with the technical design and fabrication of the accelerator
facilities supporting the project as described in the very complete and detailed Technical Design
Report released in April 2002. In addition the committee saw a significant amount of advanced
hardware existing on the KEK site. The committee did not specifically review the cost of the facility
nor the construction, installation, and commissioning schedule. Presentations and committee
discussion concentrated on the Phase 1 project. The committee congratulates the project team on itsvery excellent progress in developing the design of the accelerator complex and initiating construction.

General Comments
The JKJ Project is comprised of a state-of-the-art proton accelerator complex with associatedexperimental facilities. The accelerator facility, which was the subject of this review, consists of a
400 M eV linac, a 3 GeV rapid cycling synchrotron, and a 50 GeV synchrotron. The two
synchrotrons are designed to provide extremely high average beam power: 1 M W from the 3 GeVring and 0.75 M W from the 50 GeV ring. This performance is beyond that of any other facilities
operational in the world today. Notable pieces of the project that are currently delayed into Phase
2 include an additional 200 M eV of superconducting linac and associated waste transmutation area,
an upgrade of the M ain Ring energy from ~40 to 50 GeV, and a neutrino beam line supporting long
baseline neutrino experiments.
Performance criteria have been established for all the accelerators and advanced conceptual designs
are complete. M ajor components have been prototyped, and in the case of the linac and the 50 GeV
Main Ring many are on order.
The accelerator design and construction present a large number of challenges, most of which areassociated with the very high average beam power required from the facility. The design,
construction, installation, and (ultimately) commissioning are being under taken by a staff numbering
approximately 110 people. In the experience of the committee this appears to be a modest number
for such an ambitious and complex facility , constructed over a five-year time frame. The committee
also notes that a project of this scope comes along only infrequently and presents unique1

opportunities for the training of young people in the design, construction, and operation of a major
accelerator facility—people who become a resource for the future.
The committee heard very little on strategies for commissioning of the accelerator complex.
While we did not expect significant discussion at this meeting, the committee suggests thatthe project team assure that designs choices are made consistent with expeditious
commissioning of the facility. Presentations on commissioning strategies will become an
appropriate part of future meetings of the ATAC.

Linac
The linac consists of an (H-) ion source (IS), drift tube (DTL), separated drift tube (SDTL), andannular coupled structure (ACS) linacs. The final energy in Phase 1 is 400 M eV, with a peak currentof 50 mA, and a repetition rate of 50 Hz. The design is quite advanced and procurement of the DTL
and SDTL has begun. An ion source that nearly meets specified requirements also exists and studiesof the source and associated low energy beam transport (LEBT) line are underway. The first DTL
tank is assembled and has been aligned successfully. The first two SDTL modules have beenprocessed to approximately three times the required power. R&D aimed at finalizing the ACS isunderway. The committee offers the following specific comments and recommendations with respect
to the linac:•

The design and hardware assembled to date are basically sound and likely to deliver the
specified performance.

•

Pulse-to-pulse energy variation needs to be further understood and communicated to
the RCS design group.

•

Analysis of impact of errors and vibrations has been initiated and needs to be continued.

•

The committee supports and recommends the undertaking a complete end-to-end (IS to
RCS) multiparticle simulation, considering realistic conditions, of the linac as soon as
possible.

•

The M EBT chopper rise and fall time is a potential source of halo generation. The committee
suggests evaluation of solutions to avoid partially kicked bunches propagating through thelinac.

•The Cesium seeded filament source meets all project performance tests with the exceptionof a modest shortfall in lifetime. The committee recommends an experiment to determine
whether such a source is compatible with RFQ operations.

•

The LEBT assumes effective beam neutralization. This assumption needs to be supported
by numerical estimation or simulation.

•

The committee encourages further investigation of a design with a tapered gradient in the
upstream end of the ACS to shorten a dedicated matching section.
2

Rapid Cycling Synchrotron (RCS)The RCS is a state-of-the-art, high power, synchrotron. It is specified as providing a 3 GeV proton
beam with 8.3×1013 protons per pulse at 25 Hz repetition rate. The total delivered beam power is
1 MW.
M ultiturn injection from the linac is utilized in the RCS. Transverse and longitudinal painting, plus
a second harmonic cavity, are employed to minimize the impact of space-charge forces within thebeam. Acceleration utilizes a novel RF system. The lattice is of the “flexible momentum compaction”
type producing a higher transition energy than would be achievable with a more traditional FODO
type lattice.
A complete design concept for the RCS exists and there is active R&D on the magnet, power supply,
injection, and RF systems. However, procurements of major RCS components have not yet
been initiated and so opportunities still exist for modest design enhancements ormodifications. With this thought in mind the committee offers the following comments andrecommendations:•

The committee supports and recommend a reexamination of the optics of the linac to RCS
transfer lines, in close collaboration with the Linac group, with a goal towards improving
the acceptance. The committee supports retention of momentum collimation in any modified
design.

•The committee recommends consideration of lattice modification for the RCS based on theuse of regular FODO cells in the arcs. Such a lattice modification could offer benefits interms of increased acceptance, increased dynamic aperture, increased dispersion-free freespace, and perhaps simpler tuning. Any such benefits will have to be balanced againstcomplications in the longitudinal match of the RCS to 50 GeV Main Ring transfer.

•

Control of the tunes during RCS acceleration does not exist. The committee believes this
could compromise RCS performance and recommends the design team think about options
for introducing this capability.

•

The committee recommends the use of programmable correction dipoles in the RCS.

•

Longitudinal painting is planned to generate bunches with a hole in the longitudinal phaseplane. The attention of the project team is drawn to the fact that stability problems havebeen encountered in the CERN PS Booster under such conditions, especially when combinedwith dual harmonic operations.

•

The RF system is based on very novel, low Q, based resonators. The heavy beamloading in
the cavities will be wide-band, which will create a unique stability and beamloading
compensation problem. The committee recommends studying the problem analytically, andidentifying opportunities for experiments in existing accelerators to develop further
understanding.
3•The committee recommends the development of both tune-shift and impedance budgets for
the RCS. The committee also requests a comprehensive presentation at next year’s meetingon the subjects of impedances, instabilities, and feedback.

•The committee is not convinced of the necessity for the stranded cable in the RCS
dipole magnet.

•

The ratio between the aperture of the RCS and the collimator set position is smaller
than in some comparable machines. The committee suggests communications with
ISIS on potential collimator configurations.

50 GeV Main Ring
The 50 GeV M ain Ring is the second state-of-the-art, high power, synchrotron in the project. It is
specified as providing 50 GeV proton beam with 3.3×1014 protons per pulse with a 0.3 Hz
repetition rate. The total delivered beam power is 0.75 MW.
Injection utilizes four beam transfers from the RCS. Beam is either fast or slow extracted from the
50 GeV ring in support of a variety of high energy and nuclear physics experiments. The lattice isof the “flexible momentum compaction” type that allows acceleration of the beam without crossing
transition. In phase 1 the energy of the M ain Ring is limited to approximately 40 GeV by theabsence of an energy storage device required to reduce voltage modulation on the power grid.
A complete design for the 50 GeV M ain Ring exists and procurements of magnets and power supply
systems have been initiated. R&D continues in parallel on magnet, power supply, and RF systems.
The committee offers the following comments and recommendations with respect to the 50 GeV
Main Ring:•

The design and hardware assembled to date are basically sound and likely to deliver the
specified performance.

•

The duty factor for slow extracted beam seems to be low. The committee suggests looking
at whether the acceleration cycle could be reduced by shortening the ramp down period. It
might also be valuable to examine how the duty factor depends on the peak energy.

•

The committee recommends due consideration is taken of minimizing electron cloudformation, for example using in-situ baking of the vacuum tube, vacuum chamber surface
treatment, etc.

•

Impedances, instabilities, and damper specifications require close attention. The
committee did not receive any input on these topics at this review and requests acomprehensive presentation at next year’s meeting. Furthermore, the committee recommends
the development of both tune-shift and impedance budgets for the 50 GeV Main Ring.

•

The committee encourages consideration of a second harmonic RF cavity in the M ain Ringas part of the initial configuration.
4•The committee notes that a unique opportunity may exist for JKJ staff to participate
in the commissioning of the slow extraction system for the 120 GeV Main Injector
Ring at Fermilab later this year.

5

1

INTRODUCTION

The Accelerator Technical Advisory Committee (ATAC) for the JKJ Project held its first meetingover the period M ay 21-23, 2002 at the KEK laboratory in Tsukuba, Japan. The committee heard
presentations from project staff on the 21st through early afternoon on the 22nd, held several closed
sessions to discussion reactions and opinions, and presented a verbal report to project managementon the 23rd. The meeting agenda is attached as Appendix 3.1.
The ATAC wishes to express it appreciation to KEK and JAERI management for their hospitality
during this meeting, and to both the management and staff for their comprehensive presentations.
Committee members in attendance at this meeting included: R. Garoby/CERN,
Gardner/RAL(deputy chair), S. Holmes/Fermilab (chair), A. Noda/Kyoto, and J. Wei/BNL.

I.

Committee members absent from this meeting included: K. Bongardt/Juelich, D. Gurd/ORNL, T.
Roser/BNL, L. Young/LANL. All absent members reviewed the Technical Design Report andprovided written input to the full committee in advance of the review. In addition all members
participated in the preparation of this report.
This report summarizes the M ay 21-23 meeting. The body of this report consists of the committee’sfindings and recommendations related to the major accelerator components of the JKJ Project. Also
included are discussions of the control system and beam dynamics topics that span the individual
accelerators and allow the complex to operate efficiently as a whole. Because of the absence ofsignificant control system expertise on the ATAC at this meeting, Chapter 2.4 is provided by D.
Gurd based on his review of the Technical Design Report.

6

2

FINDINGS AND RECOMMENDATIONS

2.1

Linac

The Linac part of the JKJ accelerator complex is extensively described in the Technical Design
Report that was communicated to the members of the Accelerator Technical Advisory
Committee a few weeks before these meetings. This has been supplemented with direct interview
of members of the project team and 5 oral presentations on Tuesday 21 and Wednesday 22,May:oProject overview by Y. Yamazaki,oLinac beam dynamics by M. Ikegami,oLinac RF systems by S. Yamaguchi,oLinac accelerator components by K. Hasegawa,oBeam instrumentation in the Linac by J. Kishiro.
Moreover, we were shown the related hardware available on the KEK site, namely the filament
ion source with the LEBT, pre-chopper and 30 mA RFQ, the DTL1, a prototype SDTL tank, anumber of 324 MHz klystrons and numerous other remarkable RF equipment. Controls andVacuum issues were treated collectively with the synchrotrons. This gave us a rather complete
overview of the design principles used in the Linac and its components, as well as in the degree ofadvancement in their construction and test.

Findings
An H- source is needed to provide ~60 mA beam current during the pulses. A filament and an RF
driven versions are under development. Using Cesium, the RF driven source has already achieved
the required level of performance, except for lifetime which is still too small.
The LEBT, with solenoid focusing, has a pre-chopper to modulate the injection energy into thefollowing RFQ with rise and fall time below 50 ns. The operation with beam of a similar prechopper has been demonstrated recently on the HIMAC injector.
Two models of 4 vanes 324 MHz RFQs with pi mode stabilizing loops and electromagnetic
quadrupoles are being built. The first one, made for 30 mA beam current, has already been fully
characterized. A new one, better optimized for operation at the nominal beam current of 50 mA
is presently under construction.
After the RFQ, at 3 MeV, a MEBT equipped with RF deflectors improves the beam time
structure. The 15 ns rise and fall times of the field in the deflectors will partly kick a few bunches
at the limits of the beam pulse.
At the end of the chopping line, the beam enters a Drift Tube Linac (DTL) structure. Three
successive DTL tanks increase the beam energy up to 50 MeV. Low level measurements arepresently being made on DTL1. Preliminary measurements have also been made of the7mechanical vibrations generated by pulsing the current in the quadrupoles, and deformations havebeen found to be negligible.
At 50 MeV, the type of accelerating structures is changed to Separated Drift Tube Linac (SDTL).
Transverse focusing is also changed from FODO with a 2-beta-lambda period to Doublet with aperiod of 7-beta-lambda. The RF frequency is kept constant at this transition. The first of these
SDTL tanks has already been built and successfully conditioned up to 3 times the nominal input
RF power.
Above 190 MeV, Annular Coupled Structures (ACS) operating at 972 MHz are used. A 15.9 mlong MEBT2, equipped with buncher cavities is needed for longitudinal matching. The bunch
current is tripled inside these third harmonic resonators. The principle of the ACS structure withits bridge coupler has been demonstrated at 1296 MHz. A 972 MHz prototype is underconstruction.
At 400 MeV the L3BT beam line transports and adapts the beam to the Rapid Cycling
Synchrotron (RCS). Energy spread is reduced with a set of two debuncher cavities. Because of
the 150 mA bunch current, space charge effects have to be seriously taken into account.
The design of the 324 MHz klystron is fully mastered and a number of units have already been
produced. The development of the 972 MHz klystron is progressing satisfyingly.
Waveguide components are designed and prototypes are, or will soon be available.
The transient beam loading at 1.2 MHz induced in the accelerating structures by the chopped
beam has been investigated by the project team and the effect found negligible.
The low level RF system of the Linac is specified for stabilizing the field in the RF structureswith 1% accuracy in amplitude and 1 degree in phase. Phase stabilized optical fibers are used for
distributing the reference 12 MHz signal. Modern digital electronics is employed for I/Q
regulation, permitting high performance and sophisticated controls.
Beam instrumentation and controls are in the early stages of development.
Comments
The degree of advancement of the low energy part of the Linac is very convincing. An H- sourcewith useable characteristics has been shown to work, although the use of Cesium raises questionsof ageing and degradation of the following RFQ.
Concerning the 3 MeV chopping line and its RF deflectors, we expressed our worries about theparticles trajectories in the Linac and the losses due to the partially kicked bunches.
The committee highly appreciates the flexibility provided by the electromagnetic magnets in the
DTL.
The experimental tests of the low energy front end that is being assembled at KEK are very
important and strongly supported by the ATAC members. In a similar way, the low power
measurements of the first DTL tank (accelerating up to 20 MeV) should soon be followed by8high power tests.
Preliminary measurements of mechanical vibrations are encouraging, but further investigation on afull size DTL tank have to be planned.
The high gradient capability of the SDTL prototype comfortably exceeds the nominal
requirement.
However, the foreseen front-to-end particle tracking simulations are absolutely necessary tovalidate all design choices, especially in MEBT1 at 3 MeV and in MEBT2 at 190 MeV.
The design of the low level RF system is convincing.
Two subjects could not be treated, and should be reviewed at a later date:o debunching in the L3BT transfer line where space charge effects are still visible,
o the SC Linac
Recommendations
The detailed design of the main RF components and subsystems of the Linac have already been
completed, and prototypes of many of them have been built and tested. Their measured
characteristics and the quality of their realization leaves us no doubt that they will perform as
expected in their foreseen role. (Good advancement of the ion sources development, remarkable
performance of the 30 mA RFQ, conditioning of an SDTL prototype up to 3 times the nominal
input power, realization of full performance 324 MHz klystrons, RF deflecting cavities, highquality low level RF electronics, beam instrumentation, etc.).
In the design of the Linac accelerator itself, the explanations we were given let us think that the
choices made are workable. However, we consider that some subjects still deserve further
analysis, for which we make the following suggestions:oExperimental tests are needed for a well-informed decision on the operational
consequences of operating a high gradient RFQ on the H- beam from a source using
Cesium.

oSolutions to avoid partially kicked bunches should be pursued.

oThe possibility should be considered of using ACS sections with a progressively
increasing gradient to shorten the MEBT2 for the transition at 190 MeV between
SDTL and ACS,o

Impact of errors and vibrations, and pulse to pulse energy variation need further
investigation,oAs planned by the project team, complete front to end computer simulations of the
Linac including the L3BT line are absolutely necessary, including space charge effects
and machine imperfections, and using “realistic” particle distributions.

9

2.2

3 GeV Rapid Cycling Synchrotron (RCS)

Findings/Comments
Lattice
A good description of the RCS lattice and the injection painting scheme was provided. The
injection scheme has been well studied and appears to give good flexibility, allowing bothcorrelated and anti-correlated painting. In spite of up to 20 foil hits per proton the predicted foil
temperature is low. Multiple foil hits may lead to some beam near the acceptance limits but
initial checks do not show this.
However, the H- beam first passes through the upstream quadrupole of a cell and the extractionof the Ho/- is via a downstream quadrupole. This links the injection and ring optics, making achange of the tunes during injection complex. The experience on ISIS is that beam loss is reducedby control of the tunes & closed orbits over injection and early acceleration.
The 7 families of quadrupoles looks complex and while the advantages are given as flexibility intune value it does not appear possible to change the Q values dynamically throughout theacceleration cycle. This again is an important feature on ISIS and while the space charge tune
shift at 0.16 is much less on the RCS it may be worth adding fine tuning control to give +/- 0.2
delta Q over the acceleration cycle.
Acceleration
Restricted straight section space has lead to the use of broadband low Q cavities that achieve
considerably higher accelerating fields than ferrite loaded cavities. Promising results are reported
from prototypes. However, their use on high intensity beams must be carefully studied alongwith their use for the provision of combined harmonics. An early test on a high intensity ring
would be useful.
Extraction
The extraction system uses 7 kicker magnets and a septum magnet split into 3 sections. Kicker
impedance must be considered along with the stray field produced by the section of septum
magnet closest to the circulating beam orbit, if this has not already been done.
Magnets
Magnet designs are considered straight forward with the number of quadrupole types kept to 4.
The main magnets in the RCS are powered by individual, tracking, resonant ‘White’ circuits.
Although stranded aluminum cable is being proposed for the 25 Hz magnets to reduce the eddy
currents in the windings it was not clear that this was essential or cost effective. A technique forbrazed joins was not explained. The committee notes that B-dot for ISIS and JKJ are similar and
ISIS uses plane copper.
10

Vacuum
A novel design of ceramic vacuum chamber is proposed for the 25 Hz magnets to eliminate eddy
current effects. Ceramic sections are joined by a metal braze which is also consistent with
attaching metal end flanges to the vessel. Metalization of the ends for attaching these flanges isreported to be inconsistent with the use of a glass frit for joining the ceramic sections. Small
magnetic effects from the brazed joints are not expected.
Copper strips deposited on the outer surface of the ceramic vessels provide a RF screen. The RFcontinuity connections using capacitors have to be designed along with a method of checking theirintegrity in a radiation area. Low electron emission is achieved on the inside from a TiN coating
which will also prevent charge build up on the inside of the vessel. Impedance measurements
should be continued.
The method of vessel support in the magnets must be decided bearing in mind the magnet
vibration and the method of interconnection between vessels. If bellows are used to relieve strainsthen RF screens may be necessary in the bellows.
Lost Beam Collectors
Studies of lost beam collection indicate a high efficiency of collection. However, theApertures and Collimation limits for the Primary, Secondary and Aperture limits are 324,
~385 and 486 pi mm mr which can be compared with those proposed for the ESS
Accumulator Rings of 260, 285, 480 pi mm mr.
(Incidentally, the Injection Foil appears to be inside the collimator value of 360 pi mm mr
whereas it is normally outside the relevant y or x acceptance of 486 pi mm mr).
Adjustable collectors are the desirable solution and the methods for ensuring the arrival of the lostbeam on the collectors should be considered. On ISIS this is achieved by small, dynamic
adjustment of the closed orbit corrector magnets away from the settings that provide theminimum closed orbit error. Beam losses are adjusted while the facility is operating at 50 Hz
using 1 pulse in 50 with different closed orbit or Q values.
The mechanical design of the collector straight should allow the use of active, but not remotehandling, techniques. Interaction between JKJ and ISIS staff may prove fruitful.
GeneralFurther consideration should be given to the methods to be used for commissioning, fault finding
and error states. Personnel protection must be given the highest priority and consideration be
given to machine equipment protection from lost beam. The use of intercepting or destructive
beam monitoring will often flood or overload the machine protection systems but their use isessential.
11

While the machine shielding must comply with the local regulations a good rule of thumb is toensure that full beam loss in any area does not create radiation levels of greater than 250 µSv/h in
occupied areas.
Adequate room and lifting gear should be provided for the installation of temporary shielding for
all accelerator components above the100 MeV point.
Recommendations
Injection
Consideration of a modified lattice (as mentioned in the beam dynamics section) using FODO
arcs and matched doublet straights might create longer, free regions in the straight sections andimprove the injection scheme.
Tune Control
Consider adding fine tuning control to give +/- 0.2 delta Q over the acceleration cycle.

12

2.3

50 GeV Main Ring

Findings/Comments
The 50 GeV synchrotron is a long desired machine not only in Japan but also from the world andwill have a great impact on particle and nuclear physics when completed. Its design is presented
at the Accelerator Technical Advisory Committee held at KEK from the 21st to the 23rd in May.
Many remarkable attainments in component development are presented together with elaborate
written up proposal for the entire project. Congratulation from the heart is presented at first andthen some findings/comments on the 50 GeV main ring are summarized here.
Lattice
The lattice design with three-fold symmetry composed of usual cells of FODO structure plus
missing bend cell in addition to straight sections realizes the imaginary γt lattice, which is freefrom the transition energy in the entire energy range to be treated. The idea to adopt theimaginary γt is very interesting. The lattice preserves rather long straight sections of 116 m inorder to include all the equipments for slow extraction such as an electrostatic septum (ESS),
magnetic septa (SM) and bump magnets in the same straight section and results in a low packing
factor of the dipole in the circumference, which resulted in a rather high maximum magnetic field
as 1.9 T.
The operating point in betatron tune diagram is considered only in rather close region to theextraction resonance of 22.33. In order to make margin to the resonance during injection andacceleration, possibility of moving from appropriately far tune to the resonance after completionof acceleration should also be studied. Even with these flexibilities, the 11 quadrupole families
seem to be still too much. Careful studies on this problem is required and reasonable scheme how
to adjust these large number of quadrupoles at the commissioning stage based on observed beam
parameters should be at least clarified even if the reduction of the number of quadrupole families
is not feasible.

MagnetJudging from the results of the field measurement of radial distribution, it is well anticipated thatthe iron has already saturated to some extent at the excitation level of 50 GeV. On the other hand,the end cut structure of Rogowski’s shape is reported to be difficult to be adopted in order toavoid vibration in the iron core during ramping. Careful consideration on the saturation effect at
the higher excitation level is needed so as to realize smooth acceleration up to the top energy.
The measured results of quadrupole magnet with use of the rotating coils should be carefully
investigated from the point of view of horizontal useful aperture size. Considering the fact that13

horizontal useful aperture (132 mm) is a little bit larger than the bore diameter of the quadrupole
magnet (130 mm), field measurement system utilizing only the rotating coil system will notprovide us enough information to evaluate the homogeneity of the field gradient and its effective
length in the whole useful aperture region. Complementary measurement system of the field
gradient (G) and its integration along magnet axis(GL) in the entire useful aperture region should
be considered at least to evaluate the magnet design even if only the rotation coil is used for theroutine measurements of all the quadrupole magnets. Twin translation coils might be one ofpossible candidates. Radial structure of not only field gradient in the central region, but also theintegrated gradient along the beam axis should be paid attention. End cut shape of the quadrupole
magnets should be carefully investigated from this point of view with use of the above system.
Septum magnet with opposite field is interesting, but the effect on the circulating beam of theremnant field at injection energy should be carefully investigated in connection to the near byresonance.
Acceleration
The excitation pattern of the magnet should be flexible. The patterns of ramping up and downshould be able to be given independently by putting independent timing signals for triggering,which is inevitable to realize flexible change between slow and fast extractions. Possibility of
ramping down much faster should also be studied in order to increase the duty factor of theextracted beam. Possibility of enlarging the duty factor for lower beam energy than 50 GeVshould also be seriously investigated. Large duty factor of the beam is no less important thanhigh beam intensity for the case of counter experiments.
High field gradient cavity (~40 kV/m) loaded with magnetic alloy (MA) should be carefully
studied both theoretically and experimentally from beam dynamical point of view. Beam loadingof RF system is very high and feed-forward system should also be carefully studied.
Beam Instability
High proton beam intensity of 3.3x1014 per pulse is considered to easily induce coherent
instability. Cures for the instabilities with use of 6-pole, 8-pole, feedback damping or any othershould be proposed.
Scheme of increasing of the longitudinal emittance is required to be studied. Scheme with use ofhigher harmonics should be studied in more quantitative way. Study on beam dynamics including
beam instabilities and possible single particle resonances should be described much in detail.
VacuumRequired vacuum pressure should be carefully studied in connection with vacuum instabilities.
14

During slow beam extraction, the beam will be debunched and becomes sensitive to electron cloud
build up. For example, possibility of coating the vacuum chamber with TiN and in-situ baking
should be studied.
Proposed chamber thickness of 2 mm needs careful study about the stiffness especially the casewhen Ti alloy is adopted.
Beam Monitor
Specifications for beam diagnostics seem to be not so clear. Development of beam monitors forsuch high intensity machine should be described more clearly. The beam profile monitor with useof a sheet beam is very interesting and continuous R&D including the high intensity test at AGS
is to be considered.
Beam Extraction
Slow beam extraction assuming zero chromaticity in horizontal direction should require further
studies about the transition from finite chromaticity to suppress instabilities at the injectionenergy. The high voltage of ESS should not increase more than 200 kV if enough turn separationis realized, which might cause problem in feed through of high voltage.
GeneralMovement of the ring tunnel after magnet alignment is one of the most important issues to be
paid attention. Careful studies about the ground motion is required and enough time to wait theshrinkage of the concrete before performing precise alignment should be reserved after thecompletion of the tunnel.
Role of the abort system of 3 GeV beam in the main ring should be clearly described. Share of
the role with 50 GeV abort system should also be presented.
In order to make hands-on maintenance possible, all kickers should be designed without active
elements such as Thyratrons or IGBTs in the tunnel. Front end electronics of the beam monitors
should also be located outside of the ring tunnel. Location of various equipments should be
carefully investigated from the point of view of avoiding the radiation damage and performing
hand on maintenance.
Recommendations
1. Effect of the space charge force might become negligible at 50 GeV, but slow beam
extraction with such a high average current of 15 µA has not yet been realized. The
experience of slow beam extraction at high energy synchrotron as FNAL should bereferenced although difference of adopted resonance exists.
2. Tune flexibility during injection and acceleration is worth investigation as well as
15

commissioning strategy of adjustment of 11 quadrupole families.
3. Further beam dynamics studies on beam instabilities and so on are required.

16

2.3

Control System

It looks as if the controls team is off to an excellent start. The Technical Design Report
is quite comprehensive, the issues identified and understood, and a coherent andworkable approach is outlined. Excellent work!!
For successful integration of a complex network of accelerators such as is proposed, it is essentialthat there be one Controls Group Leader, with responsibility over control of all subsystems(vacuum, power supplies, RF, etc) and all accelerators (linac, RCS, MR). Consideration should
be given to including even conventional facilities (power, HVAC, etc), neutron choppers and thespallation target etc as well. This is implied in the brief discussion of organization, but is not
explicit.
Although not in the Controls Section, the discussion of the commissioning strategy is valuable,
and should inform the control system design. The section (5.1) on “Approach and Philosophy”
appears to be well thought out and quite complete. The simple philosophical statement that “Allinformation should be seen in the Control Room” is correct - however it is notoriously difficult toimplement in the face of pressures both for cost savings and from groups having independent
lower-level systems such as PLCs or intelligent devices. A lesson frequently learned the hardway in accelerator laboratories but not always applied is: “No hidden data.” Work hard to
enforce this approach.
The idea of using commercial products rather than in-house design wherever possible iscommon practice in new facilities, and correct here. But the advantage can be lost if care
is not take to resist the “too new” – products whose long-term reliability or market
endurance is not proven. The layered design approach is the norm today – the only reasonableapproach. The choice of EPICS is obvious, and will be beneficial. Remember that one of theprinciple benefits of EPICS is not technical – it is participation in an active community of sharedinterest and resource. Don’t solve problems that have already been addressed by others – makeuse of your worldwide EPICS collaborators. I particularly applaud the decision to use Ethernet
as a fieldbus wherever possible, and to limit the number of Ethernet controllers. This and otherchoices of standards will pay dividends, but will require effort and strong management support tomake stick.
The discussion of module selection, drivers and driver development is excellent. I wouldemphasize again however the potential value of tracking what is already available in the EPICS
community. For example, the OMS stepping motor driver is widely used in the EPICS
community and may meet the needs of this project. The discussion of PLCs and their interfaces
is very well done. I believe a statement of when, where and why PLCs will be used – i.e. for what
systems and under what circumstances – would be useful. There is a risk of an unnecessary (andcostly) PLC layer turning up with subsystems only because the subsystem engineers are
suspicious of or unfamiliar with the capabilities of EPICS. A PLC layer should be there only
where appropriate, and as a result of an agreement between the controls team and subsystem17

designers.
Network design appears well thought out, however the bulleted list of “requirements and design
criteria” (p5-5) does not really include requirements. Requirements should be stated first in termsof estimated bandwidth and reliability (and possibly security??) before arguing that theserequirements can be met using the following design criteria, and then providing the bullets. A
case needs to be made for the network redundancy that is assumed. The APS is fully redundant
but SNS felt that commercial network equipment is sufficiently reliable, and that the extra
equipment needed to provide redundancy might itself compromise reliability. I offer no opinion,
but some cost/benefit analysis would be helpful. Perhaps more should be said about security
requirements and a plan to meet them. The idea of a separate PLC network was new to me andinteresting. The proposed ClassB private IP address space is a common and flexible strategy
appropriate for the scale of this project.
The discussion of Tools, Applications and the Operator Interface demonstrates the goodunderstanding of the issues one would expect from this experienced team. The decisions and thedecision process are sound. The choice of SADScript, which worked very well for KEKB andplayed a large role in its early commissioning success, is excellent. Detailed comments on someof these issues have been listed separately.
There is a good discussion of timing system requirements (Section 6) and a preliminary indicationof how these could be met (without any discussion of technology.) Nothing is mentioned aboutline synchronization, although it may be implied in the comments on neutron choppers. Are there
challenges relating to the synchronization of line frequency, neutron choppers, RF power andextraction? Feedback is mentioned as a requirement, but there is little discussion of specificrequirements (other than for low-level RF feedback, section 3.1.3.6.3 for example). EPICS ofcourse cannot be used for fast feedback – how will any fast feedback requirements be met? The
controls interface to the chopper drive is not discussed, but is critical to operating mode selection.
The discussion of commissioning strategy touches on the operational modes, and correctly links
these to machine protection considerations. The section on machine protection (9.2.3) needs tobe expanded, although the initial breakdown into run permit, fast protect auto-rest and fast
protect latched seems entirely appropriate. The section on Personnel Safety (Section 8) considers
only shielding requirements – there is no mention of access control. Will this be theresponsibility of the Controls Group?
There is a very useful discussion of the different databases that will be required, theirrequirements and a start at considering how they might be implemented. This work should
continue at an intense level – the importance of having a coherent database strategy in place very
early in the project, with the static database for management in place and being populated as thedesign proceeds, cannot be stressed too highly. This will require work on the part of thedatabase team, but also commitment on the part of the entire project and strong support frommanagement. The dividends will be enormous.
18

Congratulations to the controls team for an excellent start.

19

2.5

Beam Dynamics

Findings
An impressive amount of design and beam-dynamics work has been done for the entire
accelerator. Due to the limited time, many subjects were not presented at the review. Excellent
work was documented in the Technical Design Report.
The design philosophy and general lattice layout of the accelerator facility have been presented.
Structural transitions occur at kinetic energies of 50 keV (Ion source to RFQ), 3 MeV (RFQ to
DTL), 50 MeV (DTL to SDTL), 191 MeV (SDTL to ACS), 400 MeV (ACS to RCS), and 3 GeV(RCS to MR). Major changes of transverse focusing type occur at energies of 50 MeV (singlet to
doublet) and 400 MeV (doublet to singlet). Major changes of acceleration frequency occur at 191
MeV (324 to 972 MHz) and 400 MeV (972 to 1.23 MHz). The linac contains a transport
section (3.0-meter MEBT1 at 3 MeV) for chopping and matching, and a section (15.9-meter
MEBT2 at 191 MeV) for matching upon frequency transition. The Linac to RCS transfer line
needs special emphasis due to the 150 mA bunch current and 100 kW average beam power. The
Rapid-cycling-synchrotron (RCS) lattice is designed with arc achromats containing missing
dipoles (six FODO-cells per arc including two missing-dipole cells) to increase the transitionenergy and synchrotron frequency. The Main Ring lattice is designed with arc achromats
containing missing-dipoles to avoid crossing transition during acceleration.
The linac is designed for H- operation at high peak intensity (50 mA). The RCS is designed for a fast
ramping (25 Hz) with high intensity (8.3 x 1013 proton per pulse). The M ain Ring is designed fora high intensity (3.3 x 1014 proton per pulse) and high brightness (4 x 1012 per eVs at tens of GeV).
Results of beam dynamics studies were presented for linac, RCS, and M ain Ring. Various computersimulation programs have been used for the study of different sections of the accelerator including
RFQ, linac, transport lines, and rings. An analysis of expected beam loss and radio-activation was
performed for the entire facility.
For the linac and connecting transport lines, single-particle dynamics and 2-D space-charge forceswere included in the basic design. Study on beam halo using 3-D space-charge model has been started(M EBT to ACS). Effects of field errors and misalignments have been partially studied. Analysis on
pulse-to-pulse beam centroid jitters, in both transverse and longitudinal directions, was not reported
in detail. On the linac structure, it was reported that the performance of the present design issuperior to the alternative structure with DTL directly connecting to ACS at a higher energy around
100 MeV.
For the Rapid-cycling-synchrotron, the tuning range of the basic lattice, not including injection
chicane and bumps, was explored. Separate studies on injection, RF, collimation, and extraction were
presented. High collimation efficiency (higher than 98%) was reported. Except for space charge,collective effects were not presented. Optical perturbation from the injection chicane and painting
bumps was reported to be 20 – 30%. A significant reduction in dynamic aperture and a large offmomentum beta-beating were reported when the two-family sextupole chromatic correction was20

applied.
For the M ain Ring, a large range of adjustment for the vertical tune and the transition energy wasreported. Effects of magnetic errors, misalignments, and space charge were studied. Intensitydependent matching was reported to be necessary. Effects of beam-environment coupling andelectron cloud were not reported.
For the transport lines connecting the rings with linac and experimental facilities, the lattice design
is not yet finalized. Beam collimation was planned. The impact of extraction-kicker malfunction isunder evaluation.
Comments
Lattice optimization is crucial to the achievement of ultimate low-loss performance of theaccelerator facility. There seems to be room for optimization on the lattice design.
Detailed study is desirable considering detailed 3-D space charge and lattice perturbations.
1) A long MEBT1 with tight focusing for chopping and anti-chopping at low energy (3MeV) is a potential source of beam halo generation. It is desirable to reserve the optics
capability of bypassing anti-chopping and possibly chopping in MEBT1, and explore afaster LEBT chopping with the goal of a shorter rise/fall time and a low beam-in-gap level.
A comparison between the present design and an alternative, shorter MEBT1 (formatching and diagnostics only) with gentle focusing can be beneficial if a realistic initial
distribution and a 3-D space-charge model are used for beam-halo investigation.
2) The change of accelerating structure, the transition from singlet to doublet focusing at anenergy of 50 MeV, and the three-time frequency jump are sources of possible beam
mismatch and halo generation. Detailed study is desirable to ensure adequate acceptancefor beam halo.
3) An all-FODO, smooth lattice is desirable for the L3BT line for matching, collimation,
diagnostics, and operational robustness. Capability of transverse and momentum
collimation is highly desirable.
4) For the RCS ring, an alternative is to use regular FODO cell instead of missing-dipole cellfor the arc. Possible advantage can be (a) an increase of the acceptance of the arc by
reducing both horizontal and vertical beta-function and the dispersion; (b) an increase in
the length of dispersion-free straight sections without significant increase in the total ring
circumference; (c) improvement of correction efficiency including both higher-orderchromaticity and off-momentum betatron function; (d) allowing chromatic sextupoles tobe distributed across the arc to avoid deterioration of the dynamic aperture; and (e) areduction of power-supply families of the quadrupoles. The disadvantage of such ascheme is the lack of synchrotron-frequency enhancement, whose impact can possibly beminimized by maintaining a high betatron tune. (For example, with a five-cell arc of cell
length 11 m, the matched, peak beta-function and dispersion can be reduced by about
30%. The length of each dispersion-free section can be increased from 3 to 4 cells. The
reduction in synchrotron frequency can be about 20%.) A long, uninterrupted straight21

section possibly realized by a doublet at the cost of increased quadrupole strengths can beadvantageous, possibly separating injection from lattice tuning (especially since anaccurate phase advance is needed for the vertical painting), reducing chicane perturbation,
allowing flexible collimator placement for increased efficiency, and reducing the number ofmagnets between secondary collimators. The optics and the extraction-channel acceptanceneed to be designed such that beam loss is tolerable when one kicker misfires, and thebeam location on neutron target does not move significantly upon kicker malfunction.
We endorse the design of Main Ring lattice to avoid transition crossing. For both RCS and Main
Ring, it is important to ensure adequate adjustability in the transverse (especially horizontal)
tunes without compromising injection, collimation, and extraction efficiency. The nominalworking points should be optimized considering nearby structure resonances and possible driving
harmonics, sensitivity to injection chicane and bump perturbation, sensitivity to collective effects
including space charge resonances and instabilities.
It is useful to monitor across the entire acceleration cycle the evolution of key, expected beam andmachine parameters including the controlled and uncontrolled beam loss, the transverse andlongitudinal acceptances, beam emittances and pulse-to-pulse centroid jitters, to ensure adequate
machine protection, tolerable radio-activation, and adequate acceptance-to-emittance ratios. An endto-end simulation needs to be performed as soon as possible, possibly with measured distribution
from the ion source, the expected field errors, and collective effects. Such an end-to-end simulation
ensures design consistency across the entire accelerator facility, and can provide valuable insights tothe basic design choices.
For the linac, it is necessary to develop a comprehensive “error budget” including field errors,
misalignment, and mechanisms (e.g. RF control inaccuracy and mechanical vibrations) leading topulse-to-pulse centroid variation. Studies should be performed to evaluate sensitivity of beamtransmission, emittance growth, and halo generation to key quantities including beam intensity, initial
beam condition, and major sources of error. Detailed 3-D simulation with focus on beam halo shouldbe performed, possibly with more than one set of codes for verification (e.g., TOUTATIS and latest
PARM TEQ for RFQ, latest PARM ILA, IM PACT, and LINSAC for the rest of linac), to ensuresatisfaction of stringent beam-loss requirements.
For the RCS and M ain Ring, it is necessary to develop a “tune-shift budget” to monitor leading
single-particle mechanisms that may compromise machine performance, including space-charge force,
chromatic effects, magnetic imperfections (geometrical, saturation, ramp-dependent, and magnet-tomagnet tracking, remnant fields from septa), magnetic fringe field, kinematic nonlinearity, chicane andbump orbit perturbation, magnet misalignments, and electron-cloud neutralization. Efforts need tobe made to reduce the impact from the major sources if their impact is significant.
For the RCS and Main Ring, it is necessary to develop an “impedance budget” to monitor leading
beam-environment coupling, and for the control of collective effects and instabilities. Efforts need
to be made to confirm by measurement, and to reduce impedance of leading sources (e.g. theimpedance of the extraction kicker modules and their power supplies) if their impact is significant.
22For the RCS, efforts need to be made to ensure an operationally reliable and robust transverse
painting, and possible momentum painting with an energy spreader.
Given the physical uncertainty of the regime of ultra-high intensity, efforts should continuously bemade develop and compare various computer simulation codes, and to benchmark these codes withexperimental machine study.
Recommendations
1. Continue the excellent design optimization, and assess possible advantage of alternative
lattice options.
2. Complete and refine end-to-end simulation incorporating realistic conditions.
3. Continue and extend beam-dynamics studies, especially on collective effects, instabilities, andelectron-cloud effects.

23

3

Appendix: Agenda for the 1st ATAC meeting (ver. 5/14/02)
Accelerator Technical Advisory Committee
Meeting Room, Bldg. 3
May 21st (Tuesday)
8:45~9:00
Welcome address:
9:00~9:15
Executive Session
9:15~9:30(Coffee break)9:30~10:00
10:00~10:45
10:45~11:30
11:30~12:15
12:15~14:00

Overview: Y. Yamazaki
Linac beam dynamics design: M. Ikegami
RCS beam dynamics design: F. Noda, K. Yamamoto
MR beam dynamics design: S. Machida(Lunch)14:00~14:20
14:20~14:40
14:40~15:10
15:10~15:40
15:40~16:10

Linac RF: S. Yamaguchi
Linac accelerator components: K. Hasegawa
Ring RF: M. Yoshii
RCS Magnet System: N. Tani, Y. Watanabe(Coffee Break)

16:10~16:25
16:25~16:40
16:40~17:00
17:00~17:10
17:10~17:30

MR M agnets: K. Niki
MR Magnet Power Supply: M. Muto
Injection/Extraction: I. Sugai, I. Sakai
Slow extraction: M. Tomizawa
Vacuum: Y. Saitoh

17:30~18:00

Executive Session

May 22nd (Wednesday)
8:45~9:05
Monitor: J. Kishiro, N. Hayashi
9:05~9:25
Control: to be proposed by J. Chiba
9:25~10:00 Beam Loss and Strategies for its Mitigation: Y. Mori
10:00~10:30 (Coffee Break)
10:30~12:00
Executive Session
and/or Reserved for the other presentations to be requested by ATAC
and/or ATAC Report Write-up
12:00~13:30 (Lunch)
13:30~18:00

ATAC Report Write-up

May 23rd(Thurdsday)
9:00~11:00 Executive Session and/or ATAC Report Write-up
11:00-12:00
Closing meeting with project management
12:00~13:30 (Lunch)
13:30 - 14:30 Executive session
2414:30 Adjourn25