NEUTRINO FACTORY AND MUON COLLIDER COLLABORATION
R&D ACTIVITIESMichael S. Zisman†
Center for Beam Physics
Accelerator & Fusion Research Division
Lawrence Berkeley National Laboratory, Berkeley, CA 94720 U.S.A.
for the Neutrino Factory and Muon Collider Collaboration

Abstract
The Neutrino Factory and Muon Collider Collaboration(MC) comprises about 140 U.S. and non-U.S. acceleratorand particle physicists. The MC is carrying out an R&D
program aimed at validating the critical design concepts
required for the construction of such machines. We arecommitted to encouraging international cooperation andcoordination of the R&D effort. Main activities of the MC
include a Targetry program, a MUCOOL program, acomponent development program, and a theory andsimulation effort. Moreover, the MC has participated inseveral feasibility studies for a complete Neutrino Factory
facility, with the aim of identifying any additional R&D
activities needed to prepare a Zeroth-order Design Report(ZDR) in about two years and a Conceptual Design report(CDR) about two years thereafter. In this paper, the R&D
goals in each area will be indicated, and the present status
and future plans of the R&D program will be described.

1 INTRODUCTION
For the past two years, the MC effort has focused
primarily on Neutrino Factory R&D topics, though Muon
Collider issues have not been ignored. (Examples include
an Emittance Exchange Workshop at BNL [1] and aHiggs Factory Collider Workshop at UCLA [2].) In
addition to the more traditional R&D activities undertakenby the MC, we have engaged in two “feasibility studies”
of a Neutrino Factory facility.
In Study-I [3], done with FNAL, technical feasibility ofan entry-level 50-GeV facility was established (assuming
the component specifications are met), and an outline of ascientifically-productive staged approach to a full facilitywas given. It was shown that a carbon target is viable foran entry-level machine. Cost drivers for the facility wereidentified, with the result that R&D on cost-effective†Supported by the U.S. Department of Energy, Division of HighEnergy Physics, under contract DE-AC03-76SF00098.

designs is now part of the overall program.
Study-II, done jointly with BNL [4, 5], was aimed at ahigher performance design. The front-end systems(capture, phase rotation, bunching, and cooling) weretreated in an integrated way. Improved understanding of
the physics requirements led to a 20 GeV beam energy.

2 COLLABORATION R&D GOALS
About one year ago, the MC created a long-range R&D
plan to cover a 5-year period. The plan was based on a“technology-limited” schedule, that is, a schedule thatassumes adequate funding would be available. At the endof the 5-year period (i.e., 4 years from now), the MC
expects to be ready to begin a formal Conceptual Design
Report (CDR) for a Neutrino Factory. Reaching this stage
implies that we are ready to design, and do a detailed costestimate, for most required components. This implies that:• all optics designs are completed and self-consistent• all validation experiments are completed, or at least
well along• concepts for all hardware are defined• prototypes for the technically challenging items arecompleted, or at least designed
As a milestone along this path, we envision preparing aZDR in about two more years. Thus far, our assumption
on funding availability has not been entirely fulfilled but,for now, we have been able to make sufficient progress toroughly maintain our technology-limited schedule.

3 R&D PROGRESS
R&D activities of the MC are organized along thefollowing lines:• Beam simulations and theory (organized by J.
Wurtele, UCB/LBNL)• Targetry experiments (organized by K. McDonald,Princeton)• MUCOOL experiments (organized by S. Geer,FNAL)• Component development
In the last category are topics such as the development of
201.25-MHz superconducting RF (SCRF) cavities atCornell, design of induction linacs for phase rotation atLBNL, design of a 20-T solenoid at BNL and MIT, anddevelopment of muon beam diagnostics, both thoseneeded for a cooling demonstration experiment and thoseneeded later for facility operation.
It is worth noting here that significant resources in thepast two years have been invested in the two feasibility
studies mentioned above. These efforts have drawn othergroups into the R&D program and have made a strong
case that a Neutrino Factory can be built.

3.1 Targetry
The goal of the targetry program is to demonstrate theperformance of MW-level targets in a high field solenoid,and, in particular, to demonstrate the lifetime of both solidand liquid targets. Plans also call for verifying pion andneutron yields.
Considerable progress has been made in the past year.
We are just beginning the E951 experimental program at
BNL after more than a year of preparation. In the firstround of experiments, a carbon target and one or moremercury targets (see Fig. 1) will be exposed to a 24 GeV
proton beam from the AGS. Strain monitors and a highspeed camera will be the primary diagnostic devices.
Simulations to assess target mechanical behavior are
under way [6]. It is worth commenting here that initialtests of a mercury jet in a high-field solenoid magnet are
being prepared by our colleagues at CERN, and we lookforward to seeing their results. Engineering of a pulsed
20-T solenoid for the E951 experiment is now
commencing; this device will be used in a subsequent
phase of the program.

Figure 1: Initial Hg target test apparatus.

3.2 MUCOOLThe MUCOOL program goals are to build component
prototypes for a cooling cell and bench test a complete
cell. The ultimate goal for this program is to test thecomplete cooling cell in a muon beam and eventually tocarry out an experimental demonstration of ionization
cooling. Though the present cooling channel designs are
based on 201.25-MHz RF components, initial component
tests, to be done this year, utilize 805-MHz components.
Normal conducting (NC) RF cavities are required tooperate at very high gradients. To improve the shunt
impedance and maximize the accelerating field on axis,
we have explored the use of Be foils to close off thecavity apertures. Thermal deformation tests have been
completed [7] with encouraging results. In addition, finiteelement calculations have been carried out [8] to validate
the model and reproduce the observed foil deformation.
One result of this work has been the use of stepped
windows to aid in heat conduction while reducing thematerial thickness near the beam axis. This approach isthe baseline for the Study-II design [4,5].
The Lab G facility at FNAL has been prepared forcarrying out high-power tests of the RF components [9].
This facility includes a 5-T solenoid having independently
powered coils and thus capable of operation in either astandard solenoid or a gradient mode [10]. Two different
cavities will be tested there in the coming months, a 6-cell
open aperture cavity (Fig. 2) and a pillbox cavity with Be
windows. Studies with the first cavity will examine highgradient limitations and studies with the second will
permit the evaluation of Be window behavior andmultipactor issues. Either cavity can be immersed in the5-T solenoidal field that represents a realistic coolingchannel environment.
A new area is presently being constructed at FNAL totest the 201.25-MHz cavities now being designed. Thisarea, which will serve initially as the site for LH2 absorber

Figure 2: Open cell 805-MHz cavity at FNAL being
tuned to final operating frequency in preparation for
high-power testing.

tests, is located at the end of the linac and will later giveaccess to the beam for component tests. It has convenient
access as well for 201.25-MHz RF power.
Absorber tests are now being readied by the Illinois
Consortium for Accelerator Research (ICAR) to occupy
the area. Pressure tests of the windows will be first,
followed eventually by thermal tests of a full system.
Very sophisticated thermal modeling is required for theabsorber design. Both internal and external heatexchanger concepts are being investigated, the former as a
joint R&D activity funded by U.S.-Japan funds.

3.3 Theory and Simulations
The goal for the beam simulation group is to complete
end-to-end simulations for a complete facility (target,capture, bunching, cooling, acceleration, storage ring),
including the effects of errors. Developing analytical tools
for understanding front-end performance is another key
activity, as is developing tools and techniques to study full
6D cooling (“emittance exchange”). Such techniques are
required for the design of an eventual muon collider andwould be helpful as well for improving the performanceof a Neutrino Factory. The simulation group also provides
support for the design of a demonstration experiment ofcooling. As described in Ref. 4, considerable progress has
been made at developing an integrated front-end design.
Analytical tools for the transverse cooling have beendeveloped [11] and work on a more generalized approachis in progress. Simulations and tracking for the acceleration and storage ring have also been undertaken. Dueto the large beam size and energy spread, these efforts
require a very detailed description of the magnetic fields.

3.4 Component Development
An important R&D area is the development of 201.25MHz SCRF cavities capable of high gradients and withadequate mechanical stiffness to avoid microphonics.
Though SCRF is by now a well-developed art, cavities at
the frequency required for muon acceleration have notbeen produced. In addition to a technical demonstration ofsuch devices, cost-effective fabrication methods must bedeveloped and tested. A test facility for this R&D
program (Fig. 3) is being built at Cornell. It will include
an enlarged clean room and high-pressure water rinsing
facility suitable for the 201.25-MHz cavity work.
Fabrication of the first 201.25-MHz SCRF test cavity, aNb-coated-copper design, has begun at CERN. Inaddition, tests have begun at INFN-Legnaro to produce aspun cavity, thus eliminating the welding step. The firsttrial will be at 500 MHz; if successful a 201.25-MHzversion will be built. Improving the quality of sputteredNb films is being studied at Beijing University using DC

Figure 3: Test facility for 201.25-MHz SCRF
cavities under construction at Cornell.
bias sputtering as opposed to the magnetron techniqueused at CERN.
Study of induction linac technology for the phaserotation section is another MC R&D activity. In Study-I,
the challenge was to provide multiple pulses for the coreson a microsecond time scale. For Study-II, the time
separation between pulses, 20 ms, is more standard forthis technology. However, the ability to combine multiple
pulse waveforms in a common core, and the identificationof the most cost-effective core material require R&D.
Plans for this are being developed. It is worth noting here
that, though large, induction linac cores of this general
size have already been successfully produced (Fig. 4) for
the DARHT project [12].

4 R&D PLANS
For the targetry program, the next steps will include
measurements of neutron and pion yields as part of theE951 experiment. Completing the design and then thefabrication of a pulsed 20-T solenoid is also a priority.
As mentioned, the MUCOOL program will shiftemphasis to the larger 201.25-MHz component
development. Developing Be windows or grid tubes forthe large aperture cavity is an R&D task in its own right.
A new solenoid for testing the RF cavities will be required
and must be designed and fabricated. Finally, developing
plans for a cooling demonstration experiment is part of themandate of this program.
There are several component development activities tobe pursued. For the SCRF cavities, the near-term plan isto fabricate a cavity with adequate mechanical stiffnessand then demonstrate high-power pulsed operation atdesign gradients of 15–20 MV/m. Design of a powersource for the RF systems is another important R&D item.
The favored approach is a multibeam klystron, possibly• Begin fabrication of high-power NCRF cavity andsuitable test solenoid• Design prototype high-power 201.25-MHz RFpower source• Complete acceleration and storage ring simulation
studies, including errors and fringe fields

5.2 FY03 (October 2002–September 2003)
During this period, major activities are expected to be:
14• Test target with solenoid at 10 ppp (~6 weeks
parasitic beam)
Figure 4: Induction linac cores fabricated at LBNL
for the DARHT project; these are representative of
the cores that would be used in a Neutrino Factory.
having 19 beams. Multibeam klystrons have been built
previously, but not at this frequency. Development of
diagnostics suitable for transporting, characterizing, andmaintaining the muon beam during cooling, acceleration,and storage must be developed. Such work has
implications as well for the anticipated coolingdemonstration, though different devices may well beneeded for the experiment.
Beam simulation work will focus on optimization toimprove cooling channel performance and exploration ofalternative approaches that have the potential for being
more cost effective. Error studies aimed at defining
component specifications will continue. Analytic work on
6D cooling and study of efficient emittance exchange
techniques will also be pursued.

5 R&D SCHEDULE
The schedule for the next several years R&D activities isreasonably well understood. As noted, however, theschedule outlined below is based on obtaining adequate
funding support, which is certainly not guaranteed.

5.1 FY02 (October 2001–September 2002)
During this period, we anticipate the following major
activities:• Begin (π, n) yield measurements to benchmark theMARS production code
• Construct a prototype carbon target• Test LH2 absorber with beam
• Test 201.25-MHz SCRF cavity (CW and pulsed)• Complete pion yield tests (~6 weeks parasiticbeam)• Begin high-power tests of 201.25-MHz NCRF
components• Begin beam tests of diagnostics devices• Integrate simulations end-to-end (target to storagering) with realistic errors and component
specifications

6 SUMMARY
The MC R&D program is vigorous and healthy at present,
though funding levels have fallen below what had been
anticipated. We have clear directions to proceed on all
R&D fronts. Long-range planning of the required R&D
program has been done. We anticipate being ready tobegin a ZDR in about 2 years and a CDR about two years
thereafter. MC membership is at a healthy level; theCollaboration is a grass-roots effort of both particle andaccelerator physicists. Though we have sufficient
manpower to carry out our program, additional groups
could be attracted to participate if support were available.
We are particularly fortunate to be joined now in thisendeavor by several NSF institutions; these university
groups are a potential source of students to participate inthis interesting R&D program. The involvement ofinternational institutions, while not formalized, is very
beneficial, and we hope to continue this positive trend.
We intend to provide detailed information to thecommunity at Snowmass’01 that will permit them toconsider and evaluate the physics potential, technicalefficacy, and R&D requirements of a Neutrino Factory.
The R&D program we are following will give the highenergy physics community the opportunity to carry out
frontier experiments in a relatively unexplored sector—anopportunity that should not be missed.

ACKNOWLEDGMENTS
The work described here represents the efforts of many
MC members. The leaders of the major R&D efforts
deserve much of the credit for guiding their programs andmaking the work happen. Support from the U.S. DOE andNSF make the work reported here possible. The special
help from FNAL and BNL managements for Study-I andStudy-II, respectively, has gone a long way towardmaking the concept of a Neutrino Factory real. Lastly, theclose interactions and cooperation with our colleagues inEurope and Japan have done much to enrich the effort ofthe MC. I am grateful for helpful comments from A.
Sessler and M. Tigner in preparing this paper.

REFERENCES[1] Emittance Exchange Workshop, BNL, September
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