Frictional Cooling Studies at Columbia University/Nevis Labs Raphael Galea, Allen Caldwell + Stefan Schlenstedt (DESY/Zeuthen) Halina Abramowitz (Tel Aviv University) Summer Students: Emily Alden Christos Georgiou Christos Georgiou Daniel Greenwald Laura Newburgh Laura Newburgh Yujin Ning Yujin Ning Will Serber Will Serber Inna Shpiro Inna Shpiro How to reduce beam Emmittance by 10 6 ?  6D,N = (  m) 3

Frictional 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 1/  2 from ionization Ionization stops, muon too slow Nuclear scattering, excitation, charge exchange, ionization

Problems/comments: large low kinetic energy  low average density (gas) Apply E  B to get below the dE/dx peak    has the problem of Muonium formation   dominates over e-stripping  in all gases except He    has the problem of Atomic capture  small below electron binding energy, but not known Slow muons don’t go far before decaying d = 10 cm sqrt(T ) T in eV so extract sideways (E  B )

Frictional Cooling: particle trajectory Some obvious statements? ** Using continuous energy loss  In 1   d  =10cm*sqrt{T(eV)}  keep d small at low T  reaccelerate quickly

Cooling cells Phase rotation sections Not to scale !!  He gas is used for  +, H 2 for  -. There is a nearly uniform 5T B z field everywhere, and E x =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).

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 ) 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

Yields & Emittance Look at muons coming out of 11m cooling cell region after initial reacceleration. Yield: approx  per 2GeV proton after cooling cell. Need to improve yield by factor 3 or more. Emittance: rms x = m y = m z = 30 m ( actually  ct) P x = 0.18 MeV P y = 0.18 MeV P z = 4.0 MeV  6D,N = (  m) 3  6D,N = (  m ) 3

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 +…

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 ?

 4 MeV p

Contains 20nm window Proton beam Gas cell Accelerating grid Vacuum chamber To MCP Si detector

Initial conclusions: no obvious cooling peak, but very low acceptance due to lack of magnetic field. Use data to tune simulations. Redo experiment with a solenoidal magnetic field.

Lab situated at MPI-WHI in Munich

Future Plans Frictional cooling tests at MPI with 5T Solenoid,  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+  ’s muon initially captured in high n orbit, then cascades down to n=1. Transition n=2  n=1 releases 2.2 KeV x-ray. Si drift detector Developed my MPI HLL

Summary of Frictional Cooling Nevis Labs work on  -  capture MPI lab for additional questions Works below the Ionization Peak Possibility to capture both signs Cooling factors O(10 6 ) or more? Still unanswered questions being worked on but work is encouraging.

Frictional Cooling: stop the  Start with low initial muon momenta  High energy  ’s travel a long distance to stop  High energy  ’s take a long time to stop

Motion in Transverse Plane Lorentz angle Assuming E x =constant

Simulations Improvements 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 )

Scattering Cross Sections Scan impact parameter  (b) to get d  /d  from which one can get mean free path Use screened Coulomb Potential (Everhart et. al. Phys. Rev. 99 (1955) 1287) Simulate all scatters  >0.05 rad

Barkas Effect 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

Target Study Cu & W, Ep=2GeV, target 0.5cm thick

Target System  cool  + &  - at the same time  calculated new symmetric magnet with gap for target

Target & Drift Optimize yield  Maximize drift length for  yield  Some  ’s lost in Magnet aperture

Phase Rotation  First attempt simple form  Vary t 1,t 2 & E max for maximum low energy yield