Transcript MICE the Muon Ionization Cooling Experiment Emilio Radicioni, INFN EPS-HEP Aachen 2003 Ionization Cooling: Theory and Practice ….maybe… The physics is straightforward … But its application.

MICE
the Muon Ionization Cooling Experiment
Emilio Radicioni, INFN
EPS-HEP Aachen 2003
Ionization Cooling: Theory and Practice
….maybe…
The physics is straightforward …
But its application in a real accelerator string is a
matter of a delicate balance of many
parameters.
Build a prototype cooling channel and evelop a
beam diagnostic able to prove that it works
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Motivations
About 20% of the cost of a Neutrino Factory is determined by the muon
cooling: the neutrino flux ultimately available for physics strongly
depends on how many muons can make it in the muon accelerator
section
Quantitative evaluation of cost trade-off between cooling and acceleration
 cost optimization of a Neutrino Factory
The physics is known, but the demonstration in practice still has to be
done
Design, build and operate a section of cooling channel capable to operate
at the desired performances
Place it in a muon beam and measure its performances in a variety of
operating modes
Show that the design tools agree with the experiment
Calibrate the simulations to make more safe to extrapolate from the
prototype cooling channel to the real one.
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Cooling
channel
• 200 MeV/c muons, 10% spread
•
x,y ~ 5cm, x’,y’ ~ 150mrad
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• 5T solenoidal fields
•201MHz RF, 8MV/m accelerating gradients
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Lattice
Average K.E.
~20 MV total
Particle loss
2D emittance
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~10%
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Quantities to be measured in a cooling experiment
Particle losses
cooling effect at nominal input
emittance: ~10%
GOAL: measure emittance reduction and transmission of the cooling channel
Check the equilibrium-emittance condition
Need to count particles (of a give type) and to measure track parameters
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MICE setup: cooling + diagnostics
Cools and measures about 100 muons/s
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Measured quantities
Complete determination of a particle beam implies measuring
Number and type of particles
x, y, t
x’=dx/dz=Px/Pz, y’=dy/dz=Py/Pz, t’=dt/dz=E/Pz
All these quantities must be measured IN and OUT of the cooling channel
When such parameters are known, the 6D emittance, as well as the 4D emittance
(ε), can be determined completely.
For a sample of N particles, one can determine the following statistical quantities:
Averages
<x>, <y>, <x’>, <y’>, etc.
Variances
2xy, … and Covariance Matrix Cxy , ..
Single-particle measurement of εin and εout ?
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Required precision and error sources
Measurements
10% emittance reduction measured to 1%  absolute errors <0.1%
Statistical
Take 106 muons to reduce statistical error to 10-3 on 
Systematic
Description of apparatus:
Detectors themselves must not spoil measurements by MCS
Magnitude (and phase) of magnetic and RF fields
Thickness/density of absorber, windows, etc.
Alignment
Beam energy scale
Simulation of MCS and dE/dx
Systematic differences between spectrometers:
Efficiency, noise differences
Mis-alignment/mis-match
Different fields
Transport: wrong particles with different kinematics will spoil the measurements
Muon in … muon out  / and /e rejection at < 1% level
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Particle-by-particle diagnostic?
Tag and identify incoming and outgoing particles  this helps in reducing
the systematic error: pion and electron contamination can spoil the
measurement. This is only possible in single-particle mode.
Correlations between phase space parameters can be easily measured
It is possible to study the effect of different beam parameters:
Energy
Transverse momentum
Input emittance
RF phase
…
Any desired input beam condition can be reconstructed from the data
sample by cutting/slicing the population of observed particles
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Detectors /trackers: baseline
•No active electronics / HV
close to liquid H2
•350m staggered fibers,
3 projections
•Key element for small X0:
VLPC readout, high
quantum efficiency
•Very good timing
(background rejection)
0.34 X0 per plane
•Modular construction
•Possibility of multiplexing
to reduce cost (related to
background issues)
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Detectors /trackers:
alternative
• Low X0 gas (0.15% X0)
• Many points per track
• High precision tracking
• Potential cost saving
• Large integration time
• Effect of X-rays on GEMs
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Backgrounds on the trackers
• Dark currents due to electron field
emission from the cavity surfaces
• Electrons are stopped in the
absorbers X-rays with wide spectrum
(brehmstrahlung) will convert in the
detector
• Quantify the problem on sample
cavity and simulate the detectors in a
flux of X-rays.
• Fibers are OK (small integration time)
but there might be a cost issue
(possibility of multiplexing)
• TPG is very light (less conversions)
but integration time is much larger.
Occupancy is the main issue.
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Approach to construction
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Challenges
High-gradient RF cavities in solenoidal fields
Operating liquid H2 absorbers with thin windows and complying with
safety regulations
Integration of cooling channel components
For cost reasons, only a small section of the cooling channel:
Emittance reduction will be about 10%  need to measure
emittance reduction at the level of 10-3
Particle detectors will have to be operated in a harsh
environment (RF and X-ray from dark current in RF cavities)
An accelerator physicist AND a particle physicist
challenge!
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