MMON Cooling : Frictional CoolingON Cooling : Frictional Cooling

A. CaldwellR. Galea C. Buettner

Project Review 11/12/03

Columbia University & the Max-Planck-Institute

OUTLINE:

• Muon Collider• Frictional Cooling• Demonstration experiment with protons at Nevis Labs • FCD experiment at MPI• Conclusions & Outlook

= 40000 ee

From target, stored

Physics at a Muon ColliderPhysics at a Muon Collider

Muon Collider Complex:• Proton Driver 2-16GeV; 1-4MW leading to 1022p/year• production target & Strong Field Capture• COOLING resultant beam• acceleration• Storage & collisions

• Stopped physics• physics• Higgs Factory• Higher Energy Frontier

Benchmark for collider:6D=1.7x10-10 (m)3 which corresponds to a reduction in initial emittance of 106

Less synchrotron radiation (~m-4)…small ring sizeLess brems, ISR… better energy determination

• Muons decay, so are not readily available – need multi MW source. Large starting cost.• Muons decay, so time available for cooling, bunching, acceleration is very limited. Need to develop new techniques, technologies.• Large experimental backgrounds from muon decays (for a collider). Not the usual clean electron collider environment.• High energy colliders with high muon flux will face critical limitation from neutrino induced radiation.

Cooler beams would allow fewer muons for a given luminosity, thereby• Reducing the experimental background• Reducing the radiation from muon decays• Allowing for smaller apertures in machine elements, and so driving the cost down

Problems…to name at least one:Problems…to name at least one:

Cooling Ideas:Cooling Ideas:

• Standard techniques… Stochastic,Electron … too slow• Nominal approach… Ionization cooling

• muons are maintained at ca. O(100 MeV) while passed successively through an energy loss medium followed by an acceleration stage• Cooling factors ~100 simulated without scheme for injection or extraction.

Frictional CoolingFrictional Cooling

• Bring muons to a kinetic energy (T) where dT/dx increases with T

• Constant E-field applied to muons resulting in equilibrium energy

• Big issue – how to maintain efficiency

• Similar idea first studied by Kottmann et al., PSI

1/2 from ionization

Ionization stops, muon too slow

Nuclear scattering, excitation, charge exchange, ionization

Problems/comments:Problems/comments:• large dE/dx @ low kinetic energy

low average density (gas)• Apply EB to get below the dT/dx

peak

• has the problem of Atomic capture small above electron binding

energy, but not known. Keep T as high as possible

• Slow muons don’t go far before decaying

d = 10 cm sqrt(T) T in eV so extract sideways (EB)• has the problem of Muonium

formation

dominates over e-strippingin all gases except He

rdx

dTBvEqF

)(

vxB dominates

E dominates

Cooling cells

Phase rotation sections

Not to scale !!

He gas is used for +, H2 for -. There is a nearly uniform 5T Bz field everywhere, and Ex =5 MV/m in gas cell region Electronic energy loss treated as continuous, individual nuclear scattering taken into account since these yield large angles.

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).

Results of simulations to this point

Oscillations about equilibrium define emittance.

Dangerous because of - capture possibility

rdx

dTBvEqF

)(

Lorentz angle drift, with nuclear scattering

Initial reacceleration regionAfter gas cell, E(z,t)

T = 4 ns at Z=444mP = 200 MeV/cEff = 40%

gas

EB

Lorentz angle

E

E

Yields & EmittanceYields & Emittance

Look at muons coming out of 11m cooling cell region after initial reacceleration.

Yield: approx 0.002 per 2GeV proton after cooling cell.Need to improve yield by factor 5 or more to match

# /proton/GeV in specifications.

Emittance: rms x = 0.015 m y = 0.036 m z = 30 m (actually ct)

Px = 0.18 MeVPy = 0.18 MeVPz = 4.0 MeV

6D,N6D,N = 5.7 10 = 5.7 10-11-11 ( (m)m)33

RAdiological Research Accelerator Facility

Perform TOF measurements with protons

2 detectors START/STOPThin entrance/exit windows for a gas cellSome density of He gasElectric field to establish equilibrium energyNO B field so low acceptance

Look for a bunching in time Can we cool protons?

TOF=T0-(Tsi-TMCP) speed Kinetic energy

The proton energy spectrum from the Si calculated using SRIM (J. F.

Ziegler, J. P. Biersack and U. Littmark, Pergamon Press, 1985). The transport through the gas performed with our detailed simulation. Need first to fix the window thickness and gas pressure.

Calibration Data:3 distances, no cell, no grid

Time resolution of system=17ns

Protons have 100-200 KeV after Si window. Good agreement with SRIM.

Pm Pt *G(t, )dt

Add cell, no gas, no E field. Extract effective window thickness by comparison with simulation. Much thicker than expected !

Add gas, still no field. Gas pressure extracted from comp. With sim. Compatible with expectations.

After background subtraction, see no hint of cooled protons. Also predicted by simulation. Problem – windows too thick, acceptance, particularly for slow protons, too small. Need to repeat the experiment with solenoid, no windows.

arXiv:physics/0311059

MPI FCD ExperimentMPI FCD Experiment

• Repeat demonstration experiment with protons • No windows, Magnetic field• 5T Superconducting Solenoid in MPI lab

HV Cable

Si Drift detector

He gas

Source

BE

,

Up to 100KV

Designs by K. Ackermann

Source

Mylar Window

Where do we get protons?Where do we get protons?• Use strong source match range to thickness in plastic• Note E||B, but protons starting from rest

Heating (cooling) to equilibrium…Heating (cooling) to equilibrium…

He

1MV/m

.9MV/m

.8MV/m

.7MV/m

.6MV/m

• Vary gas pressure/density• Vary Efield strength• Vary distance • Measure energy directly• Can our MC predict equilibrium energies?

Efield coilSupport structures

Source holder

Assorted Insulating Spacers & supportstructures

ConclusionsConclusions• Muon Collider complex would be invaluable to HEP• We need to solve the muon cooling problem

– Different schemes should be investigated• We are doing some simulation and experimental studies of frictional

cooling.– Monte Carlo simulation can provide a consistent picture under various

experimental conditions• Nevis proton frictional cooling demonstration

– Can use Monte Carlo to evaluate performance of Muon Collider based on frictional cooling…but still demonstrate

• MPI studies– New FCD experiment in house– Gas breakdown– develop experience for capture cross section measurement– Thin window issues