Transcript MUON CAPTURE IN THE FRONT END OF THE IDS NEUTRINO FACTORY D.

MUON CAPTURE IN THE FRONT END OF THE IDS NEUTRINO FACTORY
D. Neuffer, Fermilab, Batavia, IL 60510, USA, C. Rogers, RAL ASTeC Chilton, Didcot UK.,
M.
Martini and G. Prior, CERN, Genève, Suisse, C. Yoshikawa, Muons, Inc., Batavia, IL 60510
Front End – Overview
Introduction
We discuss the design of the muon capture front end of the
neutrino factory International Design Study. In the front end,
a proton bunch on a target createsz=236m
secondary pions that drift
into a capture transport channel, decaying into muons. A
sequence of rf cavities forms the resulting muon beams into
strings of bunches of differing energies, aligns the bunches to
(nearly) equal central energies, and initiates ionization
cooling. For the International Design Study (IDS), a baseline
design must be developed and optimized for an engineering
and cost study. We present a baseline design that can be
used to establish the scope of a future Neutrino Factory.
Drift from Target, Adiabatic Bunching, Bunch phaseenergy Rotation, and Initial Cooler
Simulation
Study
Results
Rf Gradient
Limitations?
Tests of 800 MHz “pillbox” rf within magnetic fields show
limitations
on LiH-based
peak gradients.
these results
Study:
Replace
coolerExtrapolation
with gas-filledoftransport
and rfto
~200 MHz rf show possible limitations on Front End rf.
cavities
πμ
μ+/10000 8GeVp
2000
1800
All μ(0.1 to 0.35GeV/c)
1600
1400
Results: Beam Cooling is significantly improved. Final emittance
is ~20% less. ~20% more beam is in neutrino factory
acceptance.
1200
1000
μ/p (εt < 0.03, εL < 0.2)
800
600
400
μ/p (εt < 0.03, εL < 0.2)
200
Mitigation Strategies
Pressurized
gas in Rotator – High Gradient rf
0
0
20
40
60
80
100
120
Neutrino Factory and Front End
140
160
180
200
220
240
260
m
A neutrino factory captures and cools muons, then accelerates
them to ~20GeV, where decays in a storage ring form
collimated multi-GeV ν-beams that can interact with a detector.
z=0m
z=80m
•Reduced
gradients in front
end: Reduction
rf gradients
in2
Study:
Use high-gradient
rf in Rotator
24 MV/mofwith
150 atm H
Buncher/Rotator
from
baseline
of ~12
MV/m to
(ρ=0.0126
gm/cm3)for
cooling
andmaximum
rf breakdown
suppression.
~6MV/m
does
not greatly
reduce
muon
capture.
(rf Reductions
Gas
replaces
cooler,
producing
shorter,
more
compact
buncher
in the Cooling section are more limiting.)
system.
•Use Be cavities; Be should have higher rf breakdown limits.
Gas-filled rf allows Higher Gradient
•Use magnetically-insulated rf cavities
z=111m
Experiments show
that rf cavities can operate z=156m
at
high gradient (~50 MV/m) with or without magnetic
fields (up to 3T tested) rf breakdown is suppressed.
2000
1800
•Use magnetically shielded rf lattice
1600
1400
z=236m
1200
1000
800
600
400
200
0
The “front end” takes π’s from the target, confining them
transversely into a drift (π→μ+ν). The beam is captured into a
string of μ bunches, the bunches are phase-energy rotated into
a string of ~200MeV/c bunches, the bunches are cooled.
p
Simulation Results:
At the end of the channel μ’s are captured in a train of
201.25 MHz bunches ~75m long (~50 bunches).
Simulations show that channel accepts ~0.14
μ+/ 8GeV p with ~0.08μ+/8GeV p within the IDS
accelerator acceptance. Both signs (μ+ and μ-) are
captured with roughly equal intensities.
FE Target
π→μ
Solenoid
Drift
Buncher
Rotator
Cooler
15 m
~65 m
~33 m
~42 m
~80 m
0
20
40
60 results
80
100 of 120
160
180
220 rotation:
240
260
ICOOL
simulation
the 140
buncher
and200phase
A: ‘s
and μ’s as produced at z=0 B: at
m the end of the solenoidal capture +
drift.(z=80m) C: ’s at z=111m after the buncher. D: ’s at z=156m,
the end of the rotator. The beam has been formed into a string of
~200MHz bunches at ~equal energies. E: At z= 236m after ~80m of
cooling. μ’s captured within rf buckets are cooled. In each plot the
vertical axis is momentum (0 to 0.6 GeV/c) and the horizontal axis is
longitudinal position (-30 to 70m).
.
rf/Magnet Requirements
Buncher-Rotator cells
The capture concept requires using relatively
high gradient rf fields interleaved with
relatively strong solenoidal magnetic fields. In
the Buncher, rf gradients of ~7MV/m at
~200MHz within 1.5T solenoids are needed.
The Rotator uses 12MV/m gradients within
1.5T, and the Cooler uses ~15MV/m within
2.7T alternating solenoid fields.
In a first approximation, the rf cavities are
copper pillbox shapes (at 200 MHz, a=0.57m,
Q=58000) and are similar to the 200 MHz rf
cavities (rounded Cu cylinders with Be
windows) built for MICE.
Table 1: Baseline rf requirements
Cooler cells
Front end Cooling
The cooling equation is:
d N
 Es2
1 dE



N
ds
 2 E ds
2 3 m  c2 LR E
The equilibrium emittance is:
 N,eq 
 Es2
2 m  c2 LR
dE
ds
Transverse rms emittance in channel
Region
Number of rf Frequencies
rf cavities
Rf gradients,
Power required
Buncher
37
0 to 7.5 MV/m,
0.5 to 3.5 MW
per frequency
Rotator
56
Cooler
100
0.02
0.0175
εt,RMS
(m)
0.015
0.0125
0.01
320 to 231.6
MHz,
13 rf frequencies
230 to 202.3
MHz,
15 rf frequencies
201.25 MHz
0.0075
12 MV/m.
~2/5 MW
per cavity
15 MV/m,
~4 MW/cavity
0.005
Buncher
0.0025
Rotator
Cooler
Acknowledgements
0
0
50
100
150
200
250
Work supported by US DOE under contract DE-AC0207CH11359 and SBIR grant DE-FG02-05ER86252.
Results: Acceptance and cooling are very good, similar to cases
with separate cooler. Example with 20 MV/m, P=133atm a bit
worse, but improved with additional cooling added at end of
Cooler/Rotator.
•Use gas-filled
in Cooling.
Study:
minimalrf gas
pressure in Rotator
H2 gas suppresses breakdown
in rf cavities,
andpressure
could be reduced to a level that is designed
Study:
H2 gas with
into the Cooler
to incorporated
suppress breakdown,
with minimal energy loss cooling. The
with good
cooling
required
pressure
is performance.
15 atm equivalent (ρ=0.00126 gm/cm3). A
study 2A configuration with either constant B-field or alternating
solenoid lattice in the Rotator was considered. In one example
the buncher rf was reduced to <6MV/m, anticipating possible
gradient limits.
Results: All of the examples showed adequate capture and
Rf experiments
will determine
gradients
bunching,
and cooling.
Alternatesafe
solenoid
latticewithin
in themagnetic
Rotator
fields; acceptance
parameters by
and~20%,
designs
to be within
reduces
butwill
canbebemodified
compensated
by the
experimentally
determined
limits.
capturing
at higher
energy. Low-density
gas-filled cavities do
not reduce performance, confirming their potential use to
prevent rf breakdown in the baseline design.
Best performance is obtained with high-pressure H2 gas
cooling in the Cooler. This was ~20% better than Study 2A
baseline.
Conclusions
We have presented a baseline design that sets the scale of the
IDS front end system. rf R&D may require changes in that
baseline, but should not change the scale of the system. That
scale will be used to obtain first-order cost and scope estimates
of a Neutrino Factory facility.
Variations that improve performance and/or reduce cost will be
considered and developed.
References
[1] “Cost-effective Design for a Neutrino Factory”, with J. S. Berg, S. A.
Bogasz, S. Caspi, J. Cobb, R. C. Fernow, J. C. Gallardo, S. Kahn, H. Kirk,
R. Palmer, K. Paul, H. Witte, M. Zisman, Phys. Rev. STAB 9,011001(2006)
[2] M. Appollonio et al., “Accelerator Concept for Future Neutrino
Facilities”, RAL-TR-2007-23, JINST 4 P07001 (2009).
[3] F. Soler et al., "Status of MICE" NuFACT09, AIP Conf. Proc. 1222, p.
288 (2010).
[4] R. Fernow, “ICOOL”, Proc. 1999 PAC, New York, p. 3020, see
http://pubweb.bnl.gov/people/fernow/
[5] T. Roberts,G4beamline,http://g4beamline.muonsinc.com
[6] C. Rogers et al., Proc. EPAC06, p.2400 (2006)
[7] D. Huang et al., Proc. PAC2009, Vancouver.
[8] D. Stratakis, J. Gallardo and R. Palmer, Proc. NuFACT09, AIP Conf.
Proc. 1222, p. 303 (2010).
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308 (2010).
[10] C. T. Rogers, Proc. NuFACT09, AIP Conf. Proc. 1222, p. 298 (2010).
[11] D. Neuffer, “‘High Frequency’ Buncher and Phase Rotation”, Proc.
NuFACT03, AIP Conf. Proc. 721, p. 407. (2004).