NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Columbia University & the Max-Planck-Institute

Review & Status of Frictional Cooling

A. Caldwell, R. Galea, D. Kollar

• Principle• Simulations• Review of Nevis Experiment• Outline next experimental steps at MPI• Summary

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

PrincipleSame as freefall and reaching terminal velocity

Gravity opposing frictionMuons energy loss in gas is compensated by applied electric field resulting in equilibrium energy

(Ionization Cooling)

• Need low energy s below ionization peak• Here energy loss is to T, the faster s lose energy faster than slow s

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Cooling aim/obvious problems• In this regime dE/dx extremely large• Slow s don’t go far before decaying d = 10 cm sqrt(T) T in eV • + forms Muonium • - is captued by Atom

• Low average density (gas)

• Apply EB to get below the dE/dx peak• Make Gas cell long as you want but transverse dimension (extraction) small.

dominates over e-strippingin all gases except He

small above electron binding energy, but not known. Keep T as high as possible

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

rdx

dTBvEqF

)(

Oscillations around equilibrium limits final emittance

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

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

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Results: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

Bunches/fill 4 4Rep. rate (Hz) 15 15p power (MW) 4 4/ bunch 2 1012 2 1012

power (MW) 4 28Wall power (MW) 120 204Collider circum. (m) 1000 6000Ave bending field (T) 4.7 5.2rms p/p (%) 0.14 0.16

6D (m)3 1.7 10 10 1.7 10 10

rms n ( mm mrad) 50 50

* (cm) 2.6 0.3

z (cm) 2.6 0.3

r spot (m) 2.6 3.2 IP (mrad) 1.0 1.1Tune shift 0.044 0.044nturns (effective) 700 785

Luminosity (cm 2 s 1) 1033 7 1034

1.7x10-10 (m)3

• Simulation of previous scheme yielded final beam emittances of 2-6x10-11 (m)3

At yields of 0.001-0.003 +/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

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

THE GOOD: Simulations include: • individual nuclear scatters• Muonium formation• - capture in H2 & He• tracking through thin windows• initial reaccelerationSufficiently cool muon beamsSufficiently cool muon beams

THE BAD:• Yields are somewhat low

THE UGLY:• Large amount of free charge which would screen field• Not simulated

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

RAdiological Research Accelerator Facility•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

Look for a bunching in time •Can we cool protons?

Nevis Experiment already reported at NuFact03R.Galea, A.Caldwell, L.Newburgh, Nucl.Instrum.Meth.A524, 27-38 (2004)arXiv: physics/0311059

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

4 MeV p

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

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

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

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

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

Low acceptance but thicker windows was the culprit

Experiment showed that MC could reproduce data under various conditions. Simulations of Frictional Cooling is promising. Exp. Confirmation still desired.

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Frictional Cooling Demonstration at MPI MunichFrictional 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.

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

HV Cable

Si Drift detector

He gas

Source

BE

,

Up to 100KV

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

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

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Heating (cooling) to equilibrium…Heating (cooling) to equilibrium…What do we expect?What do we expect?

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?

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Efield coilSupport structures

Source holder

Assorted Insulating Spacers & supportstructures

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Status of ExperimentStatus of Experiment

FWHM=250eV

• Silicon Drift Detector gives excellent resolution• Thus far Fe55 X-rays

• Cryostat & Magnet commissioned• Grid constructed & tested. Maintained 98KV in vacuum• Source & support structures constructed• Electronics & detectors available

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

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 (m)3 can be achieved & surpassed• 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 beams

Frictional Cooling is an exciting potential Frictional Cooling is an exciting potential alternative for the phase space reduction of alternative for the phase space reduction of muon beamsmuon beams

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Something about simulations• Individual nuclear scatters are simulated – crucial in determining final phase space, survival probability.

• Incorporate scattering cross sections into the cooling program

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

• Electronic energy loss treated as continuous

• Difference in + & - energy loss rates at dE/dx peak (parameterized data from Agnello et. al. (Phys. Rev. Lett. 74 (1995) 371))

• Partly due to charge exchange for +

NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan

Other problems/solutions:

B

E

• Thin windows important issue – Nevis Experiment• Breakdown in Gas Paschen Curves• Large amount of free charge which would screen field

• In ExB field particle undergoes cycloid motion limiting max kinetic energy a 2mE/B. Choose E & B appropriately to keep energy below ionization energy to prevent multiplication