Transcript Frictional Cooling - the Muon Cooling Homepage at MPI Munich

Frictional Cooling
Columbia University & the Max-Planck-Institute
R. Galea, A. Caldwell,
S.Schlenstedt, H. Abramowicz
2004 Workshop on Muon
Collider Simulation
• What is Frictional Cooling (FC)?
• Simulation of the frontend of a Muon Collider based on FC
• Targetry & Capture Magnet
• Drift Region
• Phase Rotation
• Cooling section
• Reacceleration
• Physics covered by simulations
• Energy loss mechanisms, Nuclear & electronic
• Muonium Formation
• m- capture
• Experimental results & plans
• Future studies
What is Frictional Cooling?
Nuclear scattering, atomic excitation,
charge exchange…
muon too slow to ionize
1/2 from ionization
At high energy end change is only
logarithmic whereas it is roughly
proportional to speed at low
energies
Bring muons into a kinetic energy
range where the dT/ds increases
with kinetic energy (T)
A constant
accelerating force (an
Electric field (E)) can
be applied to the
muons resulting in an
equilibrium kinetic
energy
Same as freefall and reaching
terminal velocity
Gravity opposing friction
A strong solenoidal field (B) is needed to guide the muons
until they are cooled, so apply EB to get below the dT/ds
peak

   dT
F  q( E  v  B)  rˆ
ds

   dT
F  q( E  v  B)  rˆ
ds
Oscillations around
equilibrium limits final
emittance
Yield is a critical issue:
• In this regime dT/ds extremely
large
• Slow ms don’t go far before
decaying
d = 10 cm sqrt(T) T in eV
• m+ forms Muonium
• m- is captued by Atom
s(Mm) dominates over estripping in all gases
except He
• Low average density
(gas)
• Make Gas cell long as you
want but transverse
dimension (extraction)
small.
s small above electron binding energy,
but not known. Keep T as high as
possible
Simulation of Muon Collider based on FC:
Detailed Simulation
Full MARS target simulation, optimized for low energy muon
yield: 2 GeV protons on Cu with proton beam transverse to
solenoids (capture low energy pion cloud).
Target System
• cool m+ & m- at the
same time
• calculated new
symmetric magnet with
gap for target
GeV
Target & Drift Optimize yield
• Optimize drift length for m
yield
• Some p’s lost in Magnet
aperture
• Only Muons at the end of
28m were tracked through
the rest of the system
0.4m
28m
p’s in red
m’s in green
GEANT3.21 simulation
View into beam
Phase Rotation:
• Attempt simple form
• Vary t1,t2 & Emax for maximum
low energy yield
Emax=5MV/m
t1=100ns t2=439ns
Simulation of the cooling cell:
Length=11m, Radius=0.2m
He density 1.25x10-4g/cm3
Assume uniform Bz=5T
•Muons hitting the cell walls before reaching
equil. T are considered lost
• Field extends outside
cooling cell but is damped
exponentially
• Smoothly alternate field
in order to compensate
ExB drift
Simulation of the cooling cell:
• Initial longitudinal reacceleration
to get beamlets out of cooling
section
E
Scattering Cross Sections
•Scan impact parameter and
calculate q(b), ds/dq from
which one can get lmean free path
•Use screened Coulomb
Potential (Everhart et. al. Phys. Rev. 99 (1955)
1287)
•Simulate all scatters q>0.05
rad
•Simulation accurately
reproduces ICRU tables
•Difference in m+ & menergy loss rates at dE/dx
peak
• Partly Due to charge
exchange for m+
•parameterized data from
Agnello et. al. (Phys. Rev. Lett. 74
(1995) 371)
•Only used for the electronic
part of dE/dx
Muonium Formation
Simulate the effect of muonium formation in the tracking, an
effective charge as given by sI/(sF+sI) was used
For m- the capture cross sections were parameterized and
included in the simulation
Although earlier studies
showed promising results for
m- this scheme has not been
fully investigated for this
flavor.
using calculations of Cohen (Phys.
Rev. A. Vol 62 022512-1)
Out of the Cooling Cell:
At z=11m
Beam Characterization
Muon Acceleration:
• Standalone study take the beam as described
and accelerate to a final beam momentum of
147 MeV/c at 30% survival probability
RMS 1.2MeV/c to 5MeV/c
RMS 1ms to 3ns
Results:
• Simulation of previous
scheme yielded final beam
emittances of
2-6x10-11 (pm)3
At yields of 0.001-0.003
m+/GeV proton.
• Yield could be better yet
emittance is better than
”required”
• Cooler beams
• smaller beam elements
• less background
• lower potential radiation
hazard from neutrinos
Baseline parameters for high energy muon colli ders. From “Status of Muon Colli der
Research and Development and Future Plans,” Muon Colli der Collaboration, C. M.
Ankenbrandt et al., Phys. Rev. ST Accel. Beams 2, 081001 (1999).
COM energy (TeV)
p energy ( GeV)
p’s/bunch
Bunches/fill
Rep. rate (Hz )
p power (MW)
m/ bunch
m power (MW)
Wall power (MW)
Colli der circum. (m)
Ave bending field (T)
rms p/p (%)
6D  (pm)3
rms n (p mm mrad)
* (cm)
sz (cm)
sr spot (mm)
sq IP (mrad)
Tune shift
nturns (effective)
Luminosity (cm2 s1)
0.4
16
2.5  1013
4
15
4
2  1012
4
120
1000
4.7
0.14
1.7  1010
50
2.6
2.6
2.6
1.0
0.044
700
1033
3.0
16
2.5  1013
4
15
4
2  1012
28
204
6000
5.2
0.16
1.7  1010
50
0.3
0.3
3.2
1.1
0.044
785
7  1034
1.7x10-10 (pm)3
Nevis Experiment already
reported at NuFact03
R.Galea, A.Caldwell, L.Newburgh, Nucl.Instrum.Meth.A524, 27-38 (2004)
arXiv: physics/0311059
•Perform TOF measurements with protons
•2 detectors START/STOP
•Thin entrance/exit windows for a gas
cell
•Some density of He gas
•Electric field to establish equilibrium
energy
•NO B field so low acceptance
RAdiological
Research
Accelerator
Facility
Look for a bunching in time
•Can we cool protons?
Results of RARAF experiment
• Various energies/gas
pressures/electric field strengths
indicated no cooled protons
• Lines are fits to MC & main
peaks correspond to protons
above the ionization peak
Experiment showed that MC could
reproduce data under various
conditions. Simulations of Frictional
Cooling is promising.
Exp. Confirmation still desired.
Low acceptance but thicker windows was the
culprit
Frictional Cooling Demonstration at MPI Munich
• Repeat demonstration
experiment with protons
with IMPROVEMENTS:
• No windows
• 5T Superconducting
Solenoid for high
acceptance
• Silicon detector to
measure energy directly
Cryostat housing 5T solenoid.
Status of Experiment
• Cryostat & Magnet
commissioned
• Grid constructed &
tested. Maintained 98KV
in vacuum
• Source & support
structures constructed
• Electronics & detectors
available
FWHM=250eV
• Silicon Drift Detector gives excellent resolution
• Thus far Fe55 X-rays
Summary
• Frictional Cooling is being persued as a potential cooling method
intended for Muon Colliders
• Simulations of mostly ideal circumstances show that the 6D
emittance benchmark of 1.7x10-10 (pm)3 can be achieved & surpassed
• physics/0410017
• Simulations have been supported by data from Nevis Experiment &
will be tested further at the Frictional Cooling Demonstration to take
place at MPI Munich
• Future investigations are also on the program:
• R&D into thin window or potential windowless systems
• Studies of gasbreakdown in high E,B fields
• Capture cross section measurements at m beams
Frictional Cooling is an exciting potential alternative
for the phase space reduction of muon beams intended
for a Muon Collider