MMon Coolingon CoolingRINGBERGRINGBERG

21-25 July, 200321-25 July, 2003

Studies at Columbia University/Nevis Labs & MPIStudies at Columbia University/Nevis Labs & MPIRaphael Galea, Allen CaldwellRaphael Galea, Allen Caldwell

How to reduce beam Emmittance by 106?

6D,N = 1.7 10-10 (m)3

• Why Muons, why Muon Collider?• Muon Cooling, Ionization or Frictional Cooling• Frictional Cooling with protons• Conclusions and future work

R. Galea Ringberg Workshop 21-25 July, 2003

Why a Muon Collider ?

No synchrotron radiation problem (cf electron) P (E/m)4

Can build a high energy circular accelerator.

Collide point particles rather than complex objects

P P

R. Galea Ringberg Workshop 21-25 July, 2003

Dimensions of Some Colliders discussed

R. Galea Ringberg Workshop 21-25 July, 2003

Why Cooling?

• All Colliding beams have some cooling to reduce the large phase space of initial beam

STOCHASTIC• sample particles passing cooling system• correct to mean position

ELECTRON• principle of heat exchanger

RADIATIVE• lose the hot particles

R. Galea Ringberg Workshop 21-25 July, 2003

Physics at a Muon Collider

•Stopped hysics• ν hysics• HiggsFctory• HigherEνergyFroνtier

MuoνColliderColex:• ProtoνDriver2-16GeV;1 -4MWlediνgto10 22 /yer• roductioνtrget&StroνgFieldCture• COOLINGresultνt be• ccelertioν•Storge&collisioνs

sH= 40000 seeH

From target, stored

R. Galea Ringberg Workshop 21-25 July, 2003

HIGH ENERGY MUON COLLIDER PARAMETERS

Baseline parameters for high energy muon colliders. From “Status of Muon ColliderResearch and Development and Future Plans,” Muon Collider Collaboration, C. M.Ankenbrandt et al., Phys. Rev. ST Accel. Beams 2, 081001 (1999).

COM energy (TeV) 0.4 3.0p energy (GeV) 16 16p’s/bunch 2.5 ×1013 2.5 ×1013

Buνches/fill 4 4R e.rte(Hz) 15 15ower(MW) 4 4/buνch 2×1012 2×1012

ower(MW ) 4 28W llower(MW ) 120 204Collidercircu. ( ) 1000 6000Avebeνdiνgfield(T) 4.7 5.2rsd/(%) 0.1 4 0.1 66De6,N( )3 1.7 ×10−10 1.7 ×10−10

rseν( rd) 50 50b*(c ) 2.6 0.3sz(c ) 2.6 0.3srsot( ) 2.6 3.2sθIP( rd) 1.0 1.1Tuνeshift 0.0 44 0.0 44νturνs(effective ) 700 785Luiνosity(c −2s−1) 10 33 7×1034

R. Galea Ringberg Workshop 21-25 July, 2003

’s in red ’s in green

P beam (few MW)

TargetSolenoidal Magnets: few T … 20 T

Drift region for decay 30 m

Simplified emittance estimate:At end of drift, rms x,y,z approx 0.05,0.05,10 m Px,Py,Pz approx 50,50,100 MeV/c

Normalized 6D emittance is product divided by (mc)3

drift6D,N 1.7 10-4 (m)3

Emittance needed for Muon Collider collider

6D,N 1.7 10-10(m)3

This reduction of 6 orders of magnitude must be done with reasonable efficiency !

R. Galea Ringberg Workshop 21-25 July, 2003

Some Difficulties

• 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.

R. Galea Ringberg Workshop 21-25 July, 2003

Muon Cooling

Muon Cooling is the signature challenge of a Muon Collider

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

R. Galea Ringberg Workshop 21-25 July, 2003

Cooling Ideas : Ionization Cooling

Ionization cooling (Skrinsky, Neuffer, Palmer, …): muons are maintained at ca. 200 MeV. Transverse cooling of order x20 seems feasible (see ν-factory feasibility studies 1-2). Longitudinal cooling not solved.

Gas cell

RF

beam

B

R. Galea Ringberg Workshop 21-25 July, 2003

Longitudinal Cooling via Emittance Exchange

Transform longitudinal phase space into transverse (know how to cool transverse)

Bent solenoid produces dispersion

Wedge shaped absorber

R. Galea Ringberg Workshop 21-25 July, 2003

There are significant developments in achieving 6D phase space via ionization cooling (R. Palmer, MUTAC03), but still far from 106 cooling factor.

‘Balbekov Ring’

R. Galea Ringberg Workshop 21-25 July, 2003

Frictional CoolingFrictional Cooling

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

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

• Big issue – how to maintain efficiency

• First studied by Kottmann et al., PSI

Ionization stops, muon too slow

Nuclear scattering, excitation, charge exchange, ionization

1/b2 from ionization

R. Galea Ringberg Workshop 21-25 July, 2003

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

low average density (gas)• Apply E B to get below the dE/dx

peak

• has the problem of Muonium formation

s(M)dominates over e-strippingin all gases except He

• -has the problem of Atomic captures small below electron binding

energy, but not known• Slow muons don’t go far before

decayingd = 10 cm sqrt(T) T in eV

so extract sideways (E B )

€

rF = q(

r E +

r v ×

r B ) − dT

dxˆ r

R. Galea Ringberg Workshop 21-25 July, 2003

Trajectories in detailed simulation

Final stages of muon trajectory in gas cell

Lorentz angle drift, with nuclear scattering

Transverse motion

Motion controlled by B field

Fluctuations in energy results in emittance

R. Galea Ringberg Workshop 21-25 July, 2003

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 MeV/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

R. Galea Ringberg Workshop 21-25 July, 2003

Yields & 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 3 or more.

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,N = 5.7 10-11 (m)3 6D,N = 1.7 10-10 (m )3

Results as of NUFACT02

R. Galea Ringberg Workshop 21-25 July, 2003

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?

R. Galea Ringberg Workshop 21-25 July, 2003

4 MeV p

R. Galea Ringberg Workshop 21-25 July, 2003

Contains O(10-100nm) window

Proton beam

Gas cell

Accelerating grid

Vacuum chamber

To MCP

Si detector

Assumed initial conditions•20nm C windows•700KeV protons•0.04atm He

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

R. Galea Ringberg Workshop 21-25 July, 2003

Summary of Simulations•Incorporate scattering cross sections into the cooling program•Born Approx. for T>2KeV•Classical Scattering T<2KeV

•Include - capture cross section using calculations of Cohen (Phys. Rev. A. Vol 62 022512-1)

•Difference in + & - energy loss rates at dE/dx peak•Due to extra processes charge exchange•Barkas Effect parameterized data from Agnello et. al. (Phys. Rev. Lett. 74 (1995) 371)

•Only used for the electronic part of dE/dx

•Energy loss in thin windows•For RARAF setup proton transmitted energy spectrum is input from SRIM, simulating protons through Si detector(J.F. Ziegler http://www.srim.org)

R. Galea Ringberg Workshop 21-25 July, 2003

Cool protons???

€

# Events = N ii= 300ns

750ns

∑ = 58 ± 82(55)

# Events = N ii= 300ns

400ns

∑ = −5 ± 45(49)

€

# Events = N ii= 200ns

750ns

∑ = 55 ±194(77)

# Events = N ii= 200ns

400ns

∑ = −42 ±124(77)

Background exponential with m>0

Flat constant BackgroundMC exp

R. Galea Ringberg Workshop 21-25 July, 2003

No clear sign of cooling but this is expected from lack of Magnetic field & geometric MCP acceptance aloneThe Monte Carlo simulation can provide a consistent picture under various experimental conditions Can use the detailed simulations to evaluate Muon Collider based on frictional cooling performance with more confidence….still want to demonstrate the coolingWork at MPI on further cooling demonstration experiment using an existing 5T Solenoid and develop the - capture measurement

Conclusions

A lot of interesting work and results to come.

R. Galea Ringberg Workshop 21-25 July, 2003

Lab situated at MPI-WHI inMunich

R. Galea Ringberg Workshop 21-25 July, 2003

Problems/Things to investigate…

• Extraction of s through window in gas cell •Must be very thin to pass low energy s•Must be reasonably gas tight

• Can we apply high electric fields in gas cell without breakdown (large number of free electrons, ions) ? Plasma generation screening of field. • Reacceleration & bunch compression for injection into storage ring• The - capture cross section depends very sensitively on kinetic energy & falls off sharply for kinetic energies greater than e- binding energy. NO DATA – simulations use theoretical calculation• +…

R. Galea Ringberg Workshop 21-25 July, 2003

Future Plans

• Frictional cooling tests at MPI with 5T Solenoid, alpha source• Study gas breakdown in high E,B fields• R&D on thin windows• Beam tests with muons to measure capture cross section

-+H H+ e+g’s

• muon initially captured in n=15 orbit, then cascades down to n=1. Transition n=2n=1 releases 2.2 KeV x-ray.

Si drift detectorDeveloped by MPIHLL

Summary of Frictional Cooling•Works below the Ionization Peak•Detailed simulations•Cooling factors O(106) or more? •Still unanswered questions being worked on but early results are encouraging.

Kine

tic E

nerg

y(Ke

V)

Time(ns)

Y(cm

)

X(cm)

Proton cooling test