Frictional Cooling NUFACT02

1. Frictional CoolingNUFACT02 Studies at Columbia University & Nevis Labs Raphael Galea Allen Caldwell Stefan Schlenstedt (DESY/Zeuthen) Halina Abramowitz (Tel Aviv University) Summer 2001 Students: Christos Georgiou Daniel Greenwald Yujin Ning Inna Shpiro Will Serber

2. Cooling Motivation • ms not occur naturally so produce them from p on target – p beam – decay to m • p & m beam occupy diffuse phase space • Unlike e & p beams only have limited time (tm=2.2ms) to cool and form beams • Neutrino Factory/Muon Collider Collaboration are pursuing a scheme whereby they cool ms by directing particles through a low Z absorber material in a strong focusing magnetic channel and restoring the longitudinal momentum • IONIZATION COOLING COOL ENERGIES O(200MeV) • Cooling factors of 106 are considered to be required for a Muon Collider and so far factors of 10-100 have been theoretically achieved through IONIZATION COOLING CHANNELS Raphael Galea, Columbia University NUFACT02 : Imperial College London

3. Frictional Cooling • Bring muons to a kinetic energy (T) range where dE/dx increases with T • Constant E-field applied to muons resulting in equilibrium energy Raphael Galea, Columbia University NUFACT02 : Imperial College London

4. Problems/Comments: • large dE/dx @ low kinetic energy • low average density • Apply to get below the dE/dx peak • m+has the problem of Muonium formation • s(Mm) dominates over e-stripping s in all gases except He • m-has the problem of Atomic capture • s calculated up to 80 eV not measured below ~1KeV • Cool m’s extracted from gas cell T=1ms so a scheme for reacceleration must be developed Raphael Galea, Columbia University NUFACT02 : Imperial College London

5. Frictional Cooling: particle trajectory • In 1tm dm=10cm*sqrt{T(eV)} • keep d small at low T • reaccelerate quickly ** Using continuous energy loss Raphael Galea, Columbia University NUFACT02 : Imperial College London

6. Frictional Cooling: stop the m • High energy m’s travel a long distance to stop • High energy m’s take a long time to stop Start with low initial muon momenta Raphael Galea, Columbia University NUFACT02 : Imperial College London

7. Cooling scheme • Phase rotation is E(t) field to bring as many m’s to 0 Kinetic energy as possible • Put Phase rotation into the ring Raphael Galea, Columbia University NUFACT02 : Imperial College London

8. Target System • cool m+ & m- at the same time • calculated new symmetric magnet with gap for target Raphael Galea, Columbia University NUFACT02 : Imperial College London

9. 0.4m 28m p’s in red m’s in green View into beam Raphael Galea, Columbia University NUFACT02 : Imperial College London

10. Target & Drift Optimize yield • Maximize drift length for m yield • Some p’s lost in Magnet aperture Raphael Galea, Columbia University NUFACT02 : Imperial College London

11. Phase Rotation • First attempt simple form • Vary t1,t2 & Emax for maximum low energy yield Raphael Galea, Columbia University NUFACT02 : Imperial College London

12. Frictional Cooling Channel Raphael Galea, Columbia University NUFACT02 : Imperial College London

13. Cell Magnetic Field Correction solenoid Main Ring Solenoid Extract & accelerate • Realistic Solenoid fields in cooling ring Raphael Galea, Columbia University NUFACT02 : Imperial College London

14. Simulations Improvements • Incorporate scattering cross sections into the cooling program • Born Approx. for T>2KeV • Classical Scattering T<2KeV • Include m- capture cross section using calculations of Cohen (Phys. Rev. A. Vol 62 022512-1) Raphael Galea, Columbia University NUFACT02 : Imperial College London

15. Scattering Cross Sections • Scan impact parameter q(b) to get ds/dq from which one can get lmean free path • Use screened Coloumb Potential (Everhart et. al. Phys. Rev. 99 (1955) 1287) • Simulate all scatters q>0.05 rad Raphael Galea, Columbia University NUFACT02 : Imperial College London

16. Barkas Effect • Difference in m+ & m- 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 Raphael Galea, Columbia University NUFACT02 : Imperial College London

17. Frictional Cooling: Particle Trajectory • m- use Hydrogen • Smaller Z help in scapture • Lower r fewer scatters • BUT at higher equilibrium energy • 50cm long solenoid • 10cm long cooling cells • rgas for m+ 0.7atm & m- 0.3atm • Ex=5MV/m • Bz=5T realistic field configuration Raphael Galea, Columbia University NUFACT02 : Imperial College London

18. Motion in Transverse Plane • Assuming Ex=constant Lorentz angle Raphael Galea, Columbia University NUFACT02 : Imperial College London

19. Emittance Calulation After cooling cylindrical coordinates are more natural After drift cartesian coordinates More natural Beamlet uniform z distribution: Raphael Galea, Columbia University NUFACT02 : Imperial College London

20. X 100 beamlets Beamlet coordinates: Raphael Galea, Columbia University NUFACT02 : Imperial College London

21. bct vs z for m+He on Cu

22. bct vs z for m-H on W

23. Plong vs Ptrans for m+He on CU

24. Plong vs Ptrans for m-H on W

25. Rf vs z for m+He on CU

26. Rf vs z for m-H on W

27. Conclusions For cooled m

28. Problems/Things to investigate… • Extraction of ms through window in gas cell • Must be very thin to pass low energy ms • Must be gas tight and sustain pressures O(0.1-1)atm • Can we applied high electric fields in small gas cell without breakdown? • Reacceleration & recombine beamlets for injection into storage ring • The m- capture cross section depends very sensitively on kinetic energy & fall off sharply for kinetic energies greater than e- binding energy. NO DATA – simulations use calculation • Critical path item intend to make measurement Raphael Galea, Columbia University NUFACT02 : Imperial College London

29. MCP front MCP side Accelerating Grid Work at NEVIS labs • Want to measure the energy loss, m-scapture, test cooling principle • Developing Microchannel Plate & MWPC detectors Raphael Galea, Columbia University NUFACT02 : Imperial College London Multi-Wire Proportional Chamber

30. A simpler approach • Avoid difficulties of kickers & multiple windows • Without optimization initial attempts have 60% survival & cooling factor 105 • Still need to bunch the beam in time Raphael Galea, Columbia University NUFACT02 : Imperial College London

31. Conclusions • Frictional cooling shows promise with potential cooling factors of O(105-106) • Simulations contain realistic magnet field configurations and detailed particle tracking • Built up a lab at Nevis to test technical difficulties • There is room for improvement • Phase rotation and extraction field concepts very simple • Need to evaluate a reacceleration scheme Raphael Galea, Columbia University NUFACT02 : Imperial College London

32. Summary of Frictional Cooling • Works below the Ionization Peak • Possibility to capture both signs • Cooling factors O(106) or more? • Still unanswered questions being worked on but work is encouraging. Nevis Labs work on m-scapture