Report from the
3 Meeting of the Accelerator Technical Advisory
Committee for the Japan Proton Accelerator ResearchComplex (J-PARC)
rd

March 5-6, 2004
JAERI
Tokai, Japan

Table of Contents
Page

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

1

Introduction......................................................................................................92

Findings and Recommendations

3

2.1

Linac ....................................................................................................10

2.2

3 GeV Synchrotron..............................................................................13

2.3

50 GeV Synchrotron............................................................................16

2.4

Summary of Performance with 181 MeV Linac .................................18

Appendices3.1

Meeting Agenda ..................................................................................20

EXECUTIVE SUMMARY
The Accelerator Technical Advisory Committee (ATAC) of the Japan Proton Accelerator
Research Complex (J-PARC) held its third meeting over the period March 5-6, 2004 at the
JAERI laboratory in Tokai, Japan.
The J-PARC Project was initiated in 2001 as a joint project carried out by KEK and JAERI.
When complete the facility will support research into the areas of Neutron, Nuclear, andElementary Particle Physics. The Project is approved with a budget of 151.4 billion yen forPhase 1, which now includes funds for construction of the neutrino facility originally scheduled
for Phase 2. To accommodate funding for the neutrino facility the linac energy in Phase 1 has
been formally lowered to 181 MeV (as contemplated a year ago) and the construction schedule
has been delayed a year. Phase 1 is now scheduled for completion at the end of JFY2007, with
the neutrino facility completed one year later. Recovery of the linac energy to the originallyplanned 400 MeV will cost about 8.5 billion yen and will be completed following Phase 1, overthe period JFY2008-2010. Phase 2 includes extension of the linac energy to 600 MeV,
construction of the waste transmutation facility, and upgrade of the Main Ring to 50 GeV, but is
not yet approved for construction. The committee notes that when complete J-PARC will
provide Japan with the preeminent facility for hadron sciences in the world.
The ATAC heard presentations covering the technical design and fabrication of theaccelerator facilities supporting the J-PARC Project. These presentations were well prepared andinformative, as well as being responsive to most recommendations from the March 2003 ATAC
meeting. In addition the committee toured the construction site and observed many initial
production components undergoing testing as well as significantly advanced civil construction
activities. Presentations and committee discussion concentrated on the Phase 1 project goals andthe linac energy recovery plan. The committee was very impressed with the degree of progresssince the last meeting, in particular the achievement of 30 mA of beam accelerated to 20 MeV in
the first drift tube linac tank. This performance meets the design goal of the upstream end of theaccelerator complex and portends well for the future. The ATAC congratulates the project teamon its very excellent progress.
Subsequent to this meeting the ATAC Report was presented to the International Advisory
Committee and discussed as part of their deliberations at their meeting on March 8-9, 2004.

General Comments
When completed J-PARC will be a state-of-the-art proton accelerator complex withassociated experimental facilities. The accelerator facility, which was the subject of this review,
consists of a 181 MeV linac, a 3 GeV rapid cycling synchrotron (RCS), and a 50 GeV
synchrotron denoted the Main Ring (MR), and operating with a maximum energy of 40 GeV in
Phase 1. The two synchrotrons are designed to provide extremely high average beam power: 0.6
MW from the RCS and 0.72 MW from the MR. This performance is beyond that of any otherfacility operational in the world today. Notable components of the project currently delayed
beyond Phase 1 include restoration of the full linac energy to 400 MeV, an additional 200 MeV
1

of superconducting linac and associated waste transmutation area, and realization of the full 50
GeV performance of the Main Ring. The neutrino beamline and target previously incorporated
into Phase 2 has now been funded in parallel with Phase 1.
Performance criteria have been established for all the accelerators, all major components
have been prototyped, and nearly all are currently on order.
Since the last ATAC meeting, the reduction of the linac energy in Phase 1 to 181 MeV (from400 MeV), as first proposed a year ago, has been formalized. As such the meeting of the ATAC
concentrated on issues related to facility performance based on the 181 MeV linac and plans forrecovering the energy to 400 MeV once funds become available. However, such funds are notyet committed.
The accelerator design and construction present a large number of challenges, most of which
are associated 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 130 people. While this staff is extremely dedicated and skilled, thecommittee feels, as it did last year, that the overall staffing level is modest for such an ambitious
and complex facility, constructed over a seven-year time frame. The committee is gratified tohear that increased staff have been pledged by laboratory management and suggests that theappropriate balance be maintained between new hires and reassignment of existing experienced
accelerator staff as other activities wind down at KEK and JAERI.
The committee heard for the first time presentations on beam diagnostics and strategies forcommissioning of the accelerator complex. The ATAC report provides several comments andsuggestions in these areas.
400 MeV Recovery Plan
The plan for recovering the full 400 MeV linac energy has been modified from thepreliminary plan presented to the ATAC in its last meeting. The revised plan is to fabricate andpower test Annular Coupled Structure (ACS) units offline, over the period JFY2008-2010. ACS
units are then installed on the beam line and commissioned over the second half of JFY2010.
Operations with the full 400 MeV linac energy are then initiated in early JFY 2011 with full 1
MW achieved in the RCS at the end of JFY 2012. The ATAC has the following comments
relative to the recovery plan presented at this meeting:•

The strategy of installing the ACS structures in a single shutdown, followed by
immediate commissioning and transition to operations, eliminates concerns expressed by
the ATAC last year relative to transmission of beam through idle ACS cavities in theprior recovery scheme. The ATAC is confident that 3 months are sufficient, withadequate preparation and personnel, to install and commission the ACS equipment.
Setting-up with beam of the linac and RCS are likely to take a similar duration.

•

Momentum collimation has been removed from the linac to RCS transfer line. While theperformance of the linac appears to be acceptable in terms of beam capture in the RCS,
the committee retains some concern with regard to this removal in terms of off-normal
2linac pulses.
Recommendation: The presence of a momentum collimation device in the linac to RCS
transfer line should be reconsidered.
•Achievement of the stated 3 month schedule to install the ACS followed by 3 months ofcommissioning appears aggressive and so will require detailed planning and assignmentof adequate personnel. The committee did not hear details of the plan. J-PARC
management will have to establish a plan, in consultation with users, several years inadvance of the actual upgrade.

•

The committee endorses the new strategy as minimizing risk associated with the energy
recovery, and maximizing delivered beam power to users in the interim.

•

The committee feels there is a high probability that linac performance goals for Phase 1of the project will be met.

•

However, as reflected in the discussion below the ATAC continues to believe that
restoration of the linac energy to 400 MeV is essential for realization of the original JPARC goals of 1 MW beam power from the Rapid Cycling Synchrotron and 0.75 MWfrom the 50 GeV Main Ring.
Recommendation: Recover the linac energy to 400 MeV as soon as possible.

Performance expectations with the 181 MeV linac
An energy of 181 MeV for injection into the RCS has now been formalized as the J-PARC
Phase 1 goal. Installation of the ACS linac, and realization of the full 400 MeV originallyproposed, are now delayed beyond Phase 1. Within this plan performance goals for the J-PARC
accelerator complex in Phase 1 have been established as:
3 GeV Rapid Cycling Synchrotron:

0.60 MW50 GeV Main Ring (40 GeV, fast spill)

0.72 MWThe ATAC meeting featured multiple presentations and subsequent discussion relative to themeasures being taken to maximize performance of the J-PARC accelerator complex based on thelowered linac energy, and the degree of confidence that can be assigned to projected
performance levels. With regard to RCS performance the ATAC has the following comments,
conclusions, and recommendations:•

The RCS performance goal is consistent with the 30 mA achieved in DTL tank 1.

•

Scaling the beam intensity to constant space charge results in a projection of 0.33 MW
delivered from the RCS with a 181 MeV injection energy. The committee believes 0.33
MW represents a lower limit on what will be achieved with the RCS in Phase 1.

•

Simulations presented to the ATAC indicate that a higher space charge tune shift shouldbe achievable at 181 MeV than at 400 MeV because identical beam loss, in percent,3

translates to lower lost beam power.
•

The committee believes 0.6 MW beam power with 181 MeV injection into the RCS isplausible, but requires more developed simulations and loss analysis to provide
confidence.
Recommendation: Incorporate closed orbit errors and correction , magnet errors,
resonance correction, and bunching factor variations into the RCS simulation.
Recommendation: Improve the injection simulation by identifying where the lostparticles go. Establish a budget for particles lost other than on the collimators anddemonstrate that the collimation system meets this budget.

In order to recover the maximum beam power the injection scheme into the Main Ring has
been modified from the original Phase 1 design. The Main Ring harmonic number has been
doubled to enable operations with 15 bunches, rather than the originally planned 8. With
expected bunch intensities delivered from the RCS the resultant beam power is 0.72 MW,
essentially the same as the original Phase 1 goal of 0.75 MW. However, this mode of operation
requires single bunch operation of the RCS and 15 individual injections into the MR. (The oldscheme had four transfers of two bunches each.) With regard to MR performance the ATAC has
the following comments, conclusions, and recommendations:•

RCS beamloading compensation is a greater challenge with a single bunch than with two.
Nonetheless, the committee believes it is achievable.
Recommendation: Consider the possibility of providing beam loading compensation
via feedback in addition to or instead of feedforward.

•

The MR injection time is extended from 0.12 seconds to 0.56 seconds with the new
injection scheme. The ATAC expressed concern at its last meeting with respect toperformance with an extended dwell time at the 3 GeV MR injection energy.

•

Simulations to date provide a good start on understanding the issues associated with theextended dwell time and offer encouragement that MR performance goals can beachieved. This work is going in the right direction, however the situation is complex andan integrated simulation does not yet exist.

•

If the MR were operated in the originally envisioned mode of four transfers of two
bunches each from the RCS, the achievable beam power based on the current RCS
performance goal would be 0.44 MW. The committee believes 0.44 MW represents thelikely lower limit on what will be achieved with the Main Ring in Phase 1 (40 GeV, fast
spill).

•

The committee cannot yet establish a high degree of confidence in the 0.72 MW goal for
the MR given current uncertainties in the simulations. (However, nothing has beenpresented that would preclude this.)•

Simulation of the full 0.56 second injection process is very difficult, thus some method of4extrapolation will be required.
Recommendation: The committee recommends an approach to establishing likely
performance in the MR incorporating the following elements:-

Establish a loss budget, both for particles ending up on the collimators andparticles ending up elsewhere.

-

Incorporate all possible effects into the injection simulation: magnet errors,machine apertures, closed orbit distortion and correction, resonance correction,and the impact of increased bunching factor.

-

Benchmark the simulation against an existing machine (BNL/AGS, KEK/PS, or
Fermilab/MI).

-

If indicated by the simulation, explore methods for increasing the bunching factor
at injection into the MR.

-

Estimate any longitudinal emittance growth that could lead to loss of beam from
the MR at the start of acceleration (beam outside the buckets).

-

We suggest linear extrapolation of simulated loss to 0.3 seconds (average time
which a particle stays at 3 GeV). This should be conservative as simulations show
slower than linear dependence of beam loss on time at 3 GeV.

Commissioning and Instrumentation
Preliminary strategies and planning for commissioning of the J-PARC accelerator facilities
were presented at the meeting. These presentations were augmented by descriptions of
instrumentation being prepared for the accelerators. The ATAC has the following comments andrecommendations with regard to the commissioning strategy and instrumentation:•

The strategy and plans for commissioning appear to be very comprehensive for this stageof the project.

•

Plans for providing instrumentation are well integrated and support the commissioning
plan.

•

The committee endorses the overall strategic approach to commissioning, but feels a few
aspects of the plan deserve reconsideration: First, the plan to establish first turn orbits in
the RCS and MR by utilizing low intensity beam at 1 Hz repetition rate requires theinstallation of pre-amplifiers on the BPMs in order to observe beam positions. The plan is
to utilize a small number (4-5) of pre-amps which are physically moved around as thefirst turn beam progresses. Second, the role of the high energy abort in the MR seems to
the committee to be unnecessarily restricted to a machine protection role.
Recommendation: Consider a strategy that utilizes high intensity beam (high enough to
be visible on the BPMs) run at a relatively low (~1/minute) rate for commissioning.
This will require that appropriate data is both saved and logged on individual pulses so5that it can be analyzed and guide adjustments made on a subsequent pulse. Such a data
logging capability could also serve for post-mortem analyses once the J-PARC facility
is in operation. (By “post-mortem” we mean analysis of what happened after something
goes wrong. For example, following a magnet quench in the Tevatron or in RHIC acollection of relevant data (orbits, loss monitors, voltage sensors) is frozen so that theconditions in the accelerator over the previous several hundred milliseconds can beused to reconstruct what happened.)
Recommendation: Consider utilization of the MR high energy abort for beam disposal
during the commissioning period.
•

The ATAC was not presented with plans for the high level applications programs thatwill be required to support commissioning. We would suggest a presentation at next
year’s meeting.

Machine Protection Systems
The committee was presented concepts for the machine protection system (MPS) and offers
the following comments and recommendations:•

The overall design of the linac MPS is convincing although we suspect that the reaction
time specified for beam loss below 50 MeV is unnecessarily small.

•

The machine protection strategy for the RCS and MR does not appear to be fully
developed at this time. It is unclear what damage can be done in the RCS or MR in asingle pulse accident. This is a critical question and must form the basis of the machine
protection strategy.
Recommendation: Establish the potential impact of a single pulse accident in the RCS
and MR, and reflect this information in the machine protection strategy.

•

As noted above the role of the full energy abort in the MR is not well defined andrequires further thought.

General Comments Relative to Accelerator Performance
Excellent progress has been made both on the DTL beam commissioning and on fabricationof all linac components (DTL and SDTL) required for 181 MeV operations. The full design
current of 30 mA has been transmitted through DTL tank 1 with 100% efficiency and little
tuning. Congratulations are due to the staff on this achievement. The ATAC has several
comments relative to the linac beyond those given in the previous discussions.
•

The ATAC was presented with the end-to-end simulations recommended last year. In
general these appear comprehensive and support linac performance goals. However, we
would further suggest assembling the data in a manner that allows one to see directly
apertures vs. beam envelope over the length of the linac and transfer line to the RCS(although we saw nothing to give us any real concern).
6•The RFQ runs with constant water temperature that is achieved about 60 minutes afterturn-on. Stablization could probably be achieved in a shorter period with active control.

Within regard to the RCS the ATAC has several comments and recommendations beyond
those discussed above:•

The committee is worried about the disposition of three monitors for radial position
feedback to the rf system. Care must be taken to desensitize the arrangement to closed
orbit distortions.
Recommendation: Reexamine the disposition of radial position BPMs. As analternative (or addition) consider utilization of a reference magnet.

•

The committee believes foil lifetime is a potential issue. We suggest this be examinedclosely.

•

The committee suggests that a description/simulation of the longitudinal painting scheme
be presented at next year’s meeting.

•

The impedance estimates for the RCS seem high, but were presented as being consistent
with the Keil-Schnell stability criterion.
Recommendation: Undertake a beam simulation with measured and modeled
impedances to assure stability.

•

A preliminary study of the electron cloud effect in the RCS was presented. This workneeds to be continued.
Recommendation: Apply TiN coating on as many elements as possible, not just theceramic beam tubes.

•

The field quality of the main dipoles and quadrupoles is very important particularly at the
injection energy.
Recommendation: Measurements of the field multi-poles should be performed at fields
corresponding to 400 MeV and 181 MeV injection energy under standard ramping
conditions.

•

The committee suggests that extended testing of an RCS dipole and quadrupole beundertaken with the full 25 Hz excitation profiles.

With regard to the Main Ring the ATAC has the following comments and recommendations:•

The committee heard a very interesting idea of using a pre-scatterer to limit losses on theelectrostatic septum. The committee did not hear enough to judge whether this will work,
but we encourage pursuit of this idea to establish viability.

•

There was no presentation on impedances and instabilities in the MR. The committee
remains concerned on this topic given the unprecedented beam intensities.
7

Recommendation: Prepare an impedance budget and instability analysis for the MR
including both single and multi-bunch effects. Use results of the analysis to establish
the requirements for beam dampers. Results should be presented at next year’s ATAC
meeting.
•

The committee continues to be concerned relative to beam instability during the resonant
extraction process featuring zero chromaticity and low momentum spread.
Recommendations: 1)Complete the simulation demonstrating the 1% loss criteria
during the slow extraction process.; 2)Simulate the debunching process of the beam in
the presence of the cavity impedances; and 3)Consider measures to ameliorate beamstability issues during this process, for example through implementation of a higher
frequency rf cavity.

Finally there are a few global issues that were raised at last year’s meeting that remainunresolved:•

The committee wonders if electromagnetic compatibility (EMC) is a potential issue
within the complex. Very large currents with high frequency modulation are beingtransported within the accelerators, which are not all 100% shielded. We suggest giving
some thought to potential issues.
Recommendation: Electromagnetic compatibility needs to be addressed at the projectlevel. The strategy in this respect should be presented at the next ATAC meeting.

•

The committee retains some concerns related to coordination across the the interfaces
between the various accelerators in the J-PARC complex.
Recommendation: Appoint a “accelerator physics coordinator” to globally oversee
accelerator physics design, track changes in machine configurations, and overseeinterface issues especially between the linac and RCS, between RCS and MR, andbetween RCS and the neutron target.

8

1

INTRODUCTION

The Accelerator Technical Advisory Committee (ATAC) for the J-PARC Project held its
third meeting over the period March 5-6, 2004 at the JAERI laboratory in Tokai, Japan. The
committee heard presentations from project staff on the 5th, held several closed sessions to
discuss reactions and opinions, and presented a verbal report to project management on the 6th.
The meeting agenda is attached as Appendix 3.1.
Committee members in attendance at this meeting included: R. Garoby/CERN, S.
Holmes/Fermilab (chair), A. Noda/Kyoto, T. Roser/BNL, L. Young/LANL (retired), and J.
Wei/BNL.
Committee members absent from this meeting included: K. Bongardt/Juelich, I.
Gardner/RAL (deputy chair), and D. Gurd/ORNL.
The ATAC wishes to express it appreciation to JAERI and KEK management and support
staff for their hospitality during this meeting, and to both the management and staff for theircomprehensive presentations.

92

FINDINGS & RECOMMENDATION

2.1 Linac
Since the last ATAC meeting in March 2003, the management of the J-PARC project had
both to ensure construction at the foreseen pace with a reduced budget in FY2003, to analyze theconsequence of the decision to limit the linac energy to 181 MeV in a first stage and to negotiate
correction of that decision. The Committee is pleased to report that convincing progress has beenobtained on all these fronts and that our past recommendations concerning the linac have been
properly taken into account.
In agreement with the project management, the Committee had asked in advance that thefocus of the present session should be on specific issues and the subjects of the talks havecarefully reflected that request.
The linac being both the first accelerator to be built and the one most affected by the energychange, a linac specialist in the Committee (L. Young) has been invited to a pre-meeting thattook place one day before the ATAC.
Comments
Linac design issues (from pre-meeting)
The induction cavity for the pre-chopper in the LEBT produces a very large backgroundnoise on the beam diagnostic devices. Beam tests, up to now, have not used it. However, forlonger macro pulse lengths (500 µs), the LEBT induction cavity pre-chopper will be needed toreduce the beam power deposited on the MEBT beam scraper. The Committee suggests someeffort should be expended to reduce noise from LEBT chopper. (EMC measures like better
grounding of the pre-chopper system and common mode rejection on the beam diagnostics haveto be applied)
Two SDTL cavities are powered by a single klystron by splitting the RF power by awaveguide splitter. The two SDTL cavities have been designed to have nearly equal beamloading. The relative phase of these two cavities will be controlled by the movement of tuners inthese cavities. The tuners are slow and can only be used to control the time-averaged relative
phase. The relative amplitude will be adjusted by a variable RF power splitter. The Committee
believes that in principle this system should operate satisfactorily.
Progress in linac construction
The revised schedule now foresees 6 months of beam tests on the linac in the period from
September 2006 to February 2007. Visiting the site, the Committee could indeed observe thatcivil engineering advanced rapidly and approximately according to schedule, as reported by the
project management. All DTL structures and 22 out of 32 SDTL structures are built.
30 mA of peak beam current were successfully accelerated up to 20 MeV on the DTL test
set-up, at KEK. The Committee congratulates the J-PARC linac team for this importantachievement that gives confidence in the future performance of the full linac.
Performance projections at 181 MeV
10The ATAC appreciated the study made of the consequences of the presence of idle ACS
cavities in the beam path and is convinced by the conclusions drawn. The Committee considers
as highly justified and fully supports the decision to avoid installing ACS structures in the beam
path while operating at 181 MeV.
End to end beam simulations have been made, in agreement with last year’s ATAC
recommendations. The effect of errors has been observed, with the consequence that transverse
collimation is needed to meet the RCS emittance requirement. However, for an easierinterpretation of the results, we would like future analysis to systematically indicate the ratio ofbeam size to aperture. In the longitudinal phase plane the fluctuations of the mean beam energy
at the end of the SDTL (assuming 1 % in amplitude and 1 degree in phase) are of the order of
1 MeV peak to peak. However, the debuncher brings the energy spread and fluctuation within
the requirement of the RCS. To reduce beam loss in the RCS, the Committee recommends
momentum collimation to eliminate energy tails and possible abnormal pulses with energy
outside the acceptance of the RCS.
The magnet configuration in the beam transport line at the place of the future ACS structures
has been changed putting the doublets between SDTL pairs at their final location. The
Committee is convinced of the interest of this change and approves it.
400 MeV energy recovery plan
The ACS structures will be installed during an extended shutdown followed by setting-up at
400 MeV . The ATAC is confident that 3 months are sufficient, with adequate preparation andpersonnel, to install and commission the ACS equipment. Setting-up with beam of the linac and
RCS are likely to take a similar duration.
Commissioning strategy
The successive operating modes to progressively set-up the accelerator have been definedand scheduled. The thermal analysis of RFQ performance after cold turn-on has been made. The
Committee is satisfied with this study and expects that practical means will be devised in duetime to minimize the estimated 1 hour delay before beam can be accelerated.
Detailed procedures have been elaborated for linac tuning. The study has been remarkably
well done and the ATAC is perfectly satisfied with the proposed procedure.
The development of beam diagnostics for the linac has been thoroughly described andprogress looks adequate.
The machine protection system is at an advanced design stage. The overall design isconvincing although we suspect that the reaction time specified for beam loss at low energy(below 50 MeV) is unnecessarily small.
Moreover, we feel concerned that electromagnetic interference represents a risk for thecorrect operation of the personnel and machine protection systems. We re-iterate our request thatelectromagnetic compatibility (EMC) should be addressed at the design and implementation
stages.
Recommendations
1. The presence of a momentum collimation device in the linac to RCS transfer line should be11

reconsidered.
2. Electromagnetic compatibility needs to be addressed at the project level. The
corresponding strategy should be presented at the next ATAC meeting.
3. End to end linac simulations showing the ratio of beam size to aperture are requested forthe next ATAC meeting.

122.2 3 GeV Rapid Cycling Synchrotron
The 3 GeV RCS is a state-of-the-art, high power synchrotron. It is designed to provide a 3
GeV proton beam with 8.3×1013 protons per pulse at 25 Hz repetition rate with a total delivered
beam power of 1 MW. As discussed above the beam power is estimated to be at 40-60% of thedesign intensity while operating with a 181 MeV injection energy instead of the design value of
400 MeV.
Multi-turn charge-exchange injection of H- beam from the linac is utilized in the RCS. Phase
space painting and a second harmonic rf system are used to minimize space-charge forces within
the beam. The RCS includes two technical innovations not seen in comparable machines. Low Q
cavities using FINEMET obviate the need for fast resonant frequency tuning and also support
first and second harmonic frequencies at the same time. A “flexible momentum compaction”
lattice produces a higher transition energy than would be achievable with a more traditional
FODO type lattice and allows for adjusting the momentum compaction at extraction to the Main
Ring.
The committee was given presentations that covered many issues of the design of the RCS,in particular including responses to the comments and recommendations that were raised by theprevious ATAC meeting.
Comments
The construction of the RCS is proceeding well. Civil construction is about at its halfway
point and procurement of most of the equipment has started. In particular the first production
dipole and quadrupole will be completed by April 2004 and all magnets are scheduled forcompletion by March 2005. Proper slotting of the endplates of the dipole and quadrupole
magnets reduced the eddy-current heating to less than 100 degrees Celsius. Beam commissioningof the RCS is scheduled to start in May 2007.
The rf beam loading is quite significant in the RCS and the committee was presented with afeed-forward compensation scheme. It includes harmonic amplitude and phase corrections atthree (h= 2,4,6) or six (h=1,2,3,4,5,6) frequencies depending whether two or one bunch iscirculating. Although feasible this scheme is quite complicated and will have to be adjusted
carefully throughout the acceleration ramp. A feedback scheme might be more practical andshould be explored.
The scheme to replace activated components in the RCS consists of using either a 10 T craneor air-pallets to move the components through the tunnel. To minimize radiation dose topersonnel in case of equipment failure the component replacement procedure, in particular inhigh radiation areas such as the collimation, injection and extraction areas, has to be carefullyplanned and equipment that facilitates the operation should be installed during construction. A
plan presently being developed by the project needs to be completed urgently as it may impact
construction activities.
The allowable beam losses at the collimation system are 3% with 400 MeV injection energy
and 6 % with 181 MeV injection energy assuming the majority of the losses occur at injection.
No allowable loss levels at any other areas were given to the committee. It is essential for thedevelopment of injection and acceleration schemes to have such allowable levels of controlled
and uncontrolled losses in all areas of the RCS.
13

The injection region is typically an area with high losses. The committee was presented withcalculations that showed the sensitivity of the charge-exchange injection to the distributions anderrors of the injected 400 MeV H- beam. These calculations should be extended to include 181
MeV injection, space charge of the circulating proton beam, and realistic foil deformations. All
possible losses should be identified, both controlled and uncontrolled.
Foil deformation could be a serious problem for stable operation of the RCS. More stable foil
configurations should be explored. Corner foils as planned for SNS would be more stable. This
would require vertical bump magnets or operating with a “smoke ring” in the vertical phasespace. It may also be possible to use a tubular structure of the stripping foil to increase thestability.
A machine protection system (MPS) is being developed that can quickly stop the beam at
low energy if a failure occurs. In the case of the RCS such a system will protect the ringcomponents provided that the already circulating protons in the RCS cannot cause any damage.
It should therefore be verified that a single pulse of beam cannot damage any equipment in the
RCS.
The planned beam instrumentation in the RCS consists mainly of a system of Beam Loss
Monitors (BLM) and Beam Position Monitors (BPM). Both systems are well designed allowing
for multiple readings during the 20 ms ramp time. The intensity dynamic range of the BPMs is100, which covers the possible operating scenarios well. The analog output of three equally
spaced BPMs will be used for the radial feedback loop. Equal spacing with a tune of 6.72 does
not guarantee the suppression of the effect of horizontal closed orbit distortions. The placementof these BPMs should be reevaluated. It may also be possible to operate the rf system of the RCS
without a radial loop as long as the average dipole field is reproducible and known well enough.
The average dipole field would best be obtained from a reference dipole magnet.
No final plan exists for a circulating beam profile monitor. A possible profile monitor would
look at luminescence from a sheet of nitrogen gas. Such a device would be non-destructive andnot be affected by the beam space charge. However, the increased residual gas pressure could
cause problems with electron clouds. An alternative would be an Ionization Profile Monitor(IPM) that detects electrons that are guided to the detector with a magnetic dipole field. The
magnetic guide field makes this profile monitor also insensitive to space charge. Such a profile
monitor was successfully tested at RHIC and is planned for SNS. An accurate beam profile
monitor will help to reduce losses from beam tails.
A very thorough plan to commission the whole complex was presented. The driving
consideration for the commissioning plan is to minimize activation during this period when beamlosses are unavoidable. To this effect all activities will be performed with low bunch intensity
and a low 1 Hz repetition rate. In addition it should be explored whether it would be possible tocommission the complex with individually requested beam pulses instead of repetitive operation.
This would further reduce the dose to the equipment but would require that the data acquisition
can store all relevant diagnostic information for subsequent review and correction. Such a14

flexible data acquisition system would also be very useful for post-mortem investigation of
failures during regular operation. By “post-mortem” we mean analysis of what happened aftersomething goes wrong. Fore example, following a magnet quench in the Tevatron or in RHIC acollection of relevant data (orbits, loss monitors, voltage sensors) is frozen so that the conditionsin the accelerator over the previous several hundred milliseconds can be used to reconstruct what
happened.
A first list of impedance calculations of the RCS beam line components was presented. Someof the impedances seem large. This effort should be continued. In particular, the transverse
impedance of the extraction kicker should be measured or calculated as soon as possible. The
heating of the kicker ferrite by the beam image currents should also be evaluated.
All ceramic beam pipes are being coated with TiN to reduce the secondary electron emission
yield. This should also be extended to all other surfaces including titanium sections.
The field quality of the main dipoles and quadrupoles is very important particularly at the
injection energy. Measurements of the field multi-poles should be performed at fields
corresponding to 400 MeV and 181 MeV injection energy under standard ramping conditions.
Based in these measurements non-linear correction magnets should be specified and included in
the RCS lattice. It would be prudent to have such non-linear correctors programmable.

Recommendations
1. Consider implementing RF feedback to compensate for the beam loading of the FINEMET
cavities.
2. Ensure that there is enough crane coverage to support efficient replacement of activatedring components, in particular in the collimation, extraction and injection area.
3. Develop a complete budget of the allowable levels of controlled losses in the collimatorsand the injection area dumps and uncontrolled losses everywhere else.
4. Complete detailed simulations of the charge-exchange injection that includes realistic
distributions and errors of the injected H- beam, space-charge effects of the circulating
proton beam, and foil distortions. Consider using more stable foil configurations
5. Verify that a single lost beam pulse cannot damage any equipment in the RCS.
6. Evaluate the placement of the beam position monitors used for the radial feedback loopwith regard to the suppression of the effect of closed orbit distortions. Alternatively theradial feedback loop could be replaced with the combination of a frequency loop and theaverage dipole field obtained from a reference magnet.
15

7. Evaluate beam profile instrumentation for the RCS. For example, consider installing an
Ionization Profile Monitor with electron detection.

16

2.3 50 GeV Main Ring
The Main Ring injection scheme has been modified to recover the maximum performance inthe face of reduced RCS bunch intensities based on its 181 MeV injection energy. The scheme
now requires 15 single bunch injections from the RCS rather than four 2 bunch injections in theoriginal plan. The result is an increase in the dwell time at the 3 GeV injection energy from 0.12
to 0.56 seconds. If successful this approach would preserve nearly all of the originallyestablished performance goal of 0.75MW.

Comments
The ATAC expressed concern at its last meeting with respect to MR performance with anextended dwell time at the 3 GeV injection energy. Simulations presented at this meeting, basedon a frozen model of space charge, provide a good start on understanding the issues and offer
encouragement that MR performance goals can be achieved. This work is going in the right
direction, however the situation is complex and an integrated simulation does not yet exist. Thisline of simulation should be pursued with consideration give to benchmarking against existinghigh intensity proton synchrotrons.
The idea of utilizing an upstream foil to minimize losses on the electrostatic septum for slow
extraction seems quite interesting. The concept needs further study to clarify the real situation of
the scattered beam. The committee also remains concerned about beam stability during the slow
extraction process based on the low chromaticity coupled with the low momentum spread.
More generally, there was no presentation on impedances and instabilities in the MR at thisyear’s meeting. We suggest that this topic be addressed at next year’s meeting.
BPM pre-amplifiers are used at the commissioning stage to view the beam at low intensity.
However, pre-amps are not required during full current operation. We suggest a reconsiderationof this strategy.
Due to very heavy weight of the magnets, the floor levels of the RCS and MR tunnel are
anticipated to vary after installation of the magnets. A strategic plan to attain needed precisionof the alignment of the magnets should be developed. The possibility to check the precision evenafter running is preferred.
Machine availability (which we define as the ratio of actual/scheduled running time) has notbeen discussed at the ATAC meetings, nor has the strategy to make the beam down time as short
as possible. However, the users will have certain expectations with regard to availability. We
suggest a dialog with the users to establish expectations followed by development of planning toachieve agreed upon availability goals.
In the design of the beam lines to neutrino and neutron, close collaboration between theaccelerator specialist and scientists from each research subject is required.

Recommendations17

1. Prepare an impedance budget and instability analysis for the MR including both single andmulti-bunch effects. Use results of the analysis to establish the requirements for beam
dampers. Results should be presented at next year’s ATAC meeting.
2. Complete the simulation demonstrating the 1% loss criteria during the slow extraction
process. The simulation should include the debunching process of the beam in the presenceof the cavity impedances. Consider measures to ameliorate beam stability issues during thisprocess, for example through implementation of a higher frequency rf.
3. The committee recommends an approach to establishing likely performance in the MR,
with the currently envisioned Phase 1 configuration, incorporating the following elements:-

Establish a loss budget, both for particles ending up on the collimators and particles
ending up elsewhere.

-

Incorporate all possible effects into the injection simulation: magnet errors, machine
apertures, closed orbit distortion and correction, resonance correction, and the impact
of increased bunching factor.

-

Benchmark the simulation against an existing machine (BNL/AGS, KEK/PS, or
Fermilab/MI).

-

If indicated by the simulation, explore methods for increasing the bunching factor at
injection into the MR.

-

Estimate any longitudinal emittance growth that could lead to loss of beam from the
MR at the start of acceleration (beam outside the buckets).

18

2.4 Summary of Performance Projections with 181 MeV Linac
With the revised Phase 1 baseline for the accelerator complex, the Linac output energy is
reduced from 400 MeV to 181 MeV. The design goal of beam power is reduced from 1 MW to
0.6 MW for the Rapid-Cycling-Synchrotron (RCS). The beam power for the Main Ring is
reduced from 0.75 MW to 0.72 MW with the increased number of bunches from 8 to 15.
On the Linac, a study was performed on the impact of idle ACS on the output energy spread,and concluded that the design specification of 0.1% can not be met. Based on this study, adecision was made that no idle ACS modules will be present during on-line operation. The ACS
section of the Linac will be populated with approximately 50% of doublet quadrupole magnets,
resulting in increased beam envelopes in all dimensions. After the completion of the Phase 1
project, the ACS modules and the remaining 50% of doublet quadrupole magnets will be inserted.
An end-to-end simulation was performed with PARMILA for the beam at 30 mA peak current
from the RFQ exit to RCS injection assuming RF amplitude error of 1%, phase error of 1 degree,
and various quadrupole magnet gradient errors, misalignments, and rolls.
On the RCS, the goal beam intensity is 5.0×1013 per pulse. The injection kinetic energy is
181 MeV. The injection/acceleration time is increased. The tolerable beam loss at injection isincreased from 3% to 6% based on a collimation efficiency of 97%. The RF frequencies arelowered to 0.94 MHz for the fundamental harmonic (h=2), and 1.88 MHz for the second
harmonic (h=4). The maximum peak current is reduced from 11.1 A to 6.7 A. The number of RF
cavities and their power supplies are reduced from 11 to 10. Specification for the power suppliesof the injection septum and bump magnets are reduced. A study on RF multi-harmonic beamloading compensation concluded that both 2-bunch and 1-bunch operations are possible based on
system feed-forward. A study on beam injection indicates that the reduction in stripping
efficiency is negligible if the injection straight has an acceptance of 30 mm mr. On the other
hand, deformation of the stripping foil remains a serious problem even at the reduced beam
power, especially due to reduced stopping distance and enhanced local energy deposit at 181
MeV injection energy. Considering the effect of space charge and vacuum chamber aperture but
assuming a low field error (10-4) and no closed-orbit error, computer simulation indicates that the
expected beam loss at injection is about 5%. With increased closed orbit error, the beam loss
increases dramatically. The expected beam power is 0.3 MW in order to retain the same spacecharge tune shift as the original 400-MeV operation, and less than 0.6 MW in order to keep thebeam loss below 4 kW.
On the Main Ring, the injection time is increased from 120 ms to 540 ms to populate 15
bunches in the MR with one-bunch operation in the RCS. The RF frequency is increased from
1.67-1.72 MHz to 3.34-3.44 MHz. The needed injection rise time is reduced from 300 ns to 170
ns. Computer simulation adopting a frozen space-charge model indicates a beam loss of morethan 2% in about 200 ms. An estimate on loss distribution is presented.
Comments
At last year’s review, we recommended evaluation of beam loss and radio-activation at the
reduced linac output energy, considering effects like linac resonance induced beam emittanceand halo growth, degradation due to idle ACS, enhanced magnet and power-supply errors at a19

reduced injection field in the RCS, enhanced RCS stripping loss when the injection field is not
optimized, and enhanced loss in the MR when the injection time is extended. We also
recommend that such a beam-loss model to be benchmarked with existing accelerator facilities
for a “reality check”. At this review, we were presented with many simulation results including
linac end-to-end simulation, idle ACS impact, RCS simulation including space charge, painting,and some field errors, and MR simulation with an estimate in loss distribution. In particular, weare pleased that the study on idle ACS has helped finalizing the 400 MeV recovery plan, andsimulation on RCS ad MR has resulted in consideration of implementation of ramped resonancecorrections.
At last year’s review, we recommended to appoint a coordinator to globally oversee
accelerator-physics design and interface issues, to evaluate overall fault conditions, and tomonitor across the entire acceleration cycle the evolution of key, expected beam and machineparameters including the controlled and uncontrolled beam loss, the transverse and longitudinal
acceptances, beam emittances and pulse-to-pulse centroid jitters, to ensure adequate machine
protection, tolerable radio-activation, and adequate acceptance-to-emittance ratios. We renew
this recommendation with emphasis on tracking configuration changes in an actively evolving
project, and on the integration of interface areas between various accelerator components (Linac
to RCS, RCS to MR), and between accelerator system, neutron target system, and experimental
systems especially regarding level of radio-activation, maintenance considerations, andparameter matching.
It would be important to base theoretical predictions not only on sophisticated computer
simulations but also on the understanding of the performance of existing accelerator facilities.
For example, the Linac performance could be benchmarked with that at proton linacs at LANL,
CERN, FNAL, and BNL regarding energy tail, emittance growth, beam loss, and failure
conditions. Calculation on the collimation efficiency in the RCS and MR could be benchmarked
with the performance of existing facilities like ISIS. Beam loss estimates in RCS and MR could
be benchmarked with those in existing machines like ISIS, KEK PS, BNL AGS, and FNAL
Booster.
Recommendations
1. Evaluate beam loss and radio-activation distribution across the entire accelerator complex
under the condition of reduced linac energy, taking into account realistic beam andmachine configuration including injection loss (foil scattering, H- and H0 loss), static anddynamic, systematic and random errors in magnets and power supplies, optics
perturbation across the injection chicane, and system malfunction (e.g. ion source
malfunction, noise, kicker misfire), etc.
2. Bench-mark computer simulation / theoretical prediction with machine measurements /experience at existing linacs, rapid-cycling synchrotrons, and high-intensity rings to
identify possible performance degradation mechanisms (e.g. linac energy tail, injection
efficiency, collimation efficiency, ring injection and ramping loss).
3. Appoint an “accelerator physics coordinator” to globally oversee accelerator-physics
design, to track changes in machine configuration, and to oversee interface issues
especially between linac and RCS, between RCS and MR, and between RCS and the20

neutron target.

21

3.1

Appendix: Agenda for the 3rd ATAC Meeting

Agenda of the 3rd ATAC Meeting for J-PARC Project (Tentative, 2/18
version, supplanted by 3/2 version)
5 March 2004
8:15 - 8:30

Welcome address and Project Status

8:30 - 10:00

Overview.

8:30
9:00
9:30
10:00-10:15
10:15-11:15
10:15
10:45
11:15-12:15
11:15
11:35
11:55
12:15-13:20
13:20-14:00
13:20
13:40
14:00-16:45

S. Nagamiya

Progress of design
Status of construction
Performance in the reduced energy operation
Energy recovery plan
Status of the neutrino facility
LINAC
RCS
50GeV
Coffee break

K. Hasegawa
H.Suzuki
M. Tomisawa

Commissioning strategy
LINAC
Ring

A.UenoS.Machida

Beam diagnostics
LINAC
RCS
MR

S. LeeN.Hayashi
T.Toyama

Lunch
Machine/Personnel protection
Personnel protection
Machine protection

Y. Takeuchi

H. Yoshikawa

Performances in 181MeV operation

14:00

Beam degradation passing through idle

Y. Shobuda

ACS
14:30

Beam loading issues on number ofbunches

15:00-15:15

F. Tamura

Coffee break

15:15
15:45

Reduction of the foil efficiency
RCS space-charge effect in injection

Y. Irie
F.NodaIssues related to MR dwell time

S.Machida

porch
16:15
16:45-17:15

Study on the impedance

16:45

Impedance budgets.

T.Toyama

22

17:15-19:00

Executive Session

6 March 2004
9:00 - 11:50
11:50-13:30
13:30-14:30

Executive Session
Lunch
Report to management

14:30-16:30
16:30-18:00

Site tour
Executive Session

23