TECHNICAL IMPLEMENTATION OF FEASIBILITY STUDY-II DESIGN
Michael S. Zisman†, LBNL, Berkeley, CA 94720 U.S.A.
S. Ozaki and R. Palmer, BNL, Upton, NY 11973-5000 U.S.A.
for the Neutrino Factory and Muon Collider Collaboration

Abstract
An updated Feasibility Study for a high-performance
Neutrino factory has been undertaken by Brookhaven
National Laboratory (BNL) and the Neutrino Factory andMuon Collider Collaboration (MC). We describe thetechnical implementation of the facility. Details of thekey components are shown, and R&D activities that need
to be addressed to proceed toward a facility design areindicated.

1 OVERVIEW OF FACILITY
The Feasibility Study-II [1] configuration is based on theinfrastructure available at BNL. Pions are produced by a
1-MW beam of 24-GeV protons from the AGS. The target
is a mercury jet in a 20-T solenoidal field. The captureand decay section tapers the magnetic field smoothly
down to 1.25 T. After the pions have decayed to muons,
the resulting beam has a very large transverse emittanceand a large energy spread. Phase rotation to reduce theenergy spread utilizes three induction linacs having
internal superconducting (SC) solenoidal focusing. Tobunch the beam we use two RF systems, a primary system
at 201.25 MHz and a second-harmonic system at 402.5
MHz. After bunching, the muons are cooled transversely
in a 108-m cooling channel operating at a central
momentum of 200 MeV/c. The cooling channel field istapered in stages to give a lower beta function as the beamcools. The muons are subsequently accelerated rapidly,
first to 2.5 GeV in a SC linac with solenoidal focusing andthen to 20 GeV in a four-pass recirculating linear
accelerator (RLA). The 20-GeV muon storage ring thatserves as the source of decay neutrinos has a compact
racetrack lattice with skew quadrupole focusing. For thisStudy, we assumed a detector located at the Waste
Isolation Pilot Plant (WIPP) site in Carlsbad, NM. The
experiment baseline is thus 2900 km. Though the Study
includes the requisite upgrades to the AGS and considers
possibilities for the detector, these will not be included inthis paper. Here we restrict ourselves to describing thefacility starting from the target and culminating in thestorage ring.
†Supported by the U.S. Department of Energy, Division of HighEnergy Physics, under contract DE-AC03-76SF00098.

2 TARGETThe Hg target material is introduced into the target
solenoid via a nozzle; the jet velocity is 20–30 m/s. As
shown in Fig. 1, the jet is at an angle of 100 mrad fromthe solenoid axis, and the proton beam is at an angle of67 mrad, leading to a 33 mrad crossing angle between thebeam and the jet. Beam pulses arrive in trains of six
bunches spaced by 20 ms, with the trains coming at a 2.5Hz rate. Thus, the instantaneous pulse rate is 50 Hz but
the average rate is only 15 Hz.
The 20-T target solenoid comprises several nested
coils. The inner three coils use normal conducting hollowconductor technology. These are surrounded by asuperconducting outer coil. There is also an iron plug,
through which both the proton beam and the Hg-jet enter,that serves to make the field more uniform at the jet entry
point. In view of the high-radiation in the target area, thecomplete facility (Fig. 2) is well shielded and designed topermit remote handling of components needing
maintenance or replacement.

3 PHASE ROTATION
To improve the channel performance, we use threeinduction linacs with differing polarity and pulse length.
IL-1 is 100 m long; IL-2 and IL-3 are each 80 m in length.
The first two units operate at a gradient of 1.5 MV/m, thethird operates at 1 MV/m. All three cores areFigure 1: Schematic of target area showing target
and beam orientation and beam dump.

16 K He Tubes
4 K He Tubes
Gas Cooled Leads
Cryostat Vacuum Port

H2-He
Heat Exchanger

HTS Leads

Coil Support30 K Shield

Radial Cold
Mass Support

LH2 AbsorberLongitudinal
Cold Mass Support
0400800

LH2 Pump

millimeters

Figure 2: Illustration of target facility showing
shielding and remote access capability.
mechanically identical, with an inner radius of 0.5 m andan outer radius of about 0.87 m. These parameters are
similar to cores built for the DARHT accelerator [2]. Theunits will be driven by magnetic pulse compressors
feeding suitable pulse forming networks. Superconducting
solenoids are incorporated into the structure as indicatedin Fig. 3.

4 BUNCHING AND COOLING
The cooling scheme is based on the SFOFO lattice type[1]. There are two different cell lengths, 2.75 m for theinitial portion (“Lattice 1”) and 1.65 m for the finalportion (“Lattice 2”). Within each lattice, the magnetic
field is increased in three stages. The last stage of Lattice
2 reaches a field of 5 T. A cross section of a Lattice 2 cellis shown in Fig. 4.

Figure 4: Cross section of Lattice 2 cell.
The RF system uses 201.25 MHz normal conducting(NC) multicell RF cavities operating at gradients of 16–17
MV/m. Though the choice of frequency has not been truly
optimized, it represents a sensible compromise between
the conflicting needs for a large beam aperture and a highaccelerating gradient. To increase the shunt impedance
and on-axis accelerating field, the cavities are closed off
with stepped Be windows [3]. Simulations have shownthat this approach does not compromise the beam cooling
effect of the channel.
The LH2 absorbers are located between RF cavities. As
indicated in Fig. 4, services are provided in the gap
between solenoid coils. The absorbers require thin Al
windows to contain the 1.2 atm liquid; suitable designs
have been developed.
Solenoid magnets to provide the required field profile
have been designed. The most challenging of these are thefocusing coils surrounding the LH2 absorbers in Lattice 2,
where the forces are large. Designs that accommodate
these forces have been developed.

5 ACCELERATION

Figure 3: Induction linac cells, showing internal
SC solenoids.

The acceleration scheme, comprises a 433 m SC preaccelerator linac followed by an RLA to reach 20 GeV.
The SC linac has three different types of modules, short,intermediate, and long. Figure 5 shows the intermediate
length module components. Each SCRF cavity is twocells, with a power coupler for each. The solenoids in thisarea are designed with an outer bucking coil and external
shielding to reduce the fringe fields at the SCRF cavities
to acceptable levels. Parameters for the SCRF system aresummarized in Table 1.
In the RLA, quadrupole triplets are used for beamfocusing. The overall system can accept the beam fromthe cooling channel and accelerate it to 20 GeV with onlymodest losses.

8000
15 00

25 0

5 00

4 601 00050 0150 050 0

Figure 5: Intermediate length cell of SC linac.
Table 1: Main SCRF parameters.
No. of cryomodules
No. of 2-cell cavities
No. of input couplers
Overall length [m]Active length [m]Filling factor
Total voltage [GV]Average real-estate gradient [MV/m]
Total heat load [kW]at 2.5K/5–8K/40–80K
aCryogenic load [kW]at 2.5K/5–8K/40–80Kb
AC power for refrigeration [MW]cTotal peak RF power [MW]Average RF power [MW]dAC Power for RF [MW]Total AC Power [MW]91299
5981015449
0.44
7.5
7.4
7.4/9.4/94
11.1/14.1/141
12.6 MW362 MW
16.3
35.6
48a

With 50% safety factor.
Assuming efficiency multipliers of 600, 225 , 20 at 2.5K, 5–8K,and 40–80K, respectively.
cWith 20% margin for control/losses.
dEfficiency multiplier = 2.
b6 STORAGE RINGThe 20-GeV storage ring layout and optics are shown inFig. 6. As designed, about 40% of the muon decays willproduce neutrinos for the detector; if decays produced in
the matching portion of the straight section must beexcluded, the percentage of usable decays will decrease
somewhat. To aim at a detector 2900 km distant, the ringis tilted by 13º. To avoid penetration of the local watertable at BNL, the ring will be partially above ground andshielded with a man-made hill.
The ring magnets are superconducting, with a field of
about 7 T. Pancake coils above and below the medianplane provide a dipole field while longitudinal staggering
between upper and lower coils provides a strong skew
quadrupole component. Attention is being paid toensuring that field harmonics are acceptable for dynamic
aperture, a nontrivial exercise for this design.

7 R&D ITEMSThe MC has a substantial R&D program now under way[4]. Here we list only topics directly related to Study-II:

Figure 7: Layout (top) and optics (bottom) of20 GeV muon storage ring.

• Verify Hg-jet performance and yield• Test induction linac with internal SC solenoid andpulsed-power supply• Verify gradient of NCRF cavities with solenoid• Demonstrate means to counter multipactor• Develop RF power source (multibeam klystron)• Develop 201.25 MHz SCRF cavities• Build shielded solenoids for preacceleration linac• Verify harmonic content of storage ring magnets• Define and test diagnostics

ACKNOWLEDGMENTS
The work described here represents the efforts of many
Study-II participants. The leaders of the major sections, T.
Roser, K. McDonald, H. Ravn, H. Kirk, L. Reginato, M.
A. Green, R. Rimmer, V. Lebedev, S. Berg, and B. Parker
deserve the credit for guiding their programs. Help from
BNL management for Study-II has gone a long way
toward making the concept of a Neutrino Factory real.

REFERENCES[1] R. Palmer, S. Ozaki, and M. Zisman, “A Second
Feasibility Study of a Muon Storage Ring Neutrino
Source, these proceedings.
[2] M. J. Burns, et al., “DARHT Accelerators Updateand Plans for Initial Operation,” in Proc. 1999
Particle Accel. Conf., p. 617.
[3] D. Li, J. Corlett, N. Hartman, S. Skar, M. Leung, andD. Lozano, “Be Window Studies at Room
Temperature,” see http://www-mucool.fnal.gov/mcnotes/muc0110.ps; N. Hartman, D. Li, and J.
Corlett, “Thin Beryllium Windows—Analysis andDesign Status,” see http://www-mucool.fnal.gov/mcnotes /muc0180.pdf.
[4] M. S. Zisman, “Neutrino Factory and Muon Collider
Collaboration R&D Activities,” these proceedings.