1. Rol Johnson 6/22/2005 NuFact05 Plenary 1 Technical Challenges of Muon Colliders Rolland P. Johnson Technical Challenges of Muon Colliders Rolland P. Johnson Muon Colliders need small muon flux to reduce proton driver demands, detector backgrounds, and site boundary radiation levels. Extreme beam cooling is therefore required to produce high luminosity at the beam-beam tune shift limit and to allow the use of high frequency RF for acceleration to very high energy in recirculating Linacs. Muon Colliders need small muon flux to reduce proton driver demands, detector backgrounds, and site boundary radiation levels. Extreme beam cooling is therefore required to produce high luminosity at the beam-beam tune shift limit and to allow the use of high frequency RF for acceleration to very high energy in recirculating Linacs. I will briefly describe 7 new ideas that are driven by these requirements, where some of the ideas may be useful for Neutrino Factories I will briefly describe 7 new ideas that are driven by these requirements, where some of the ideas may be useful for Neutrino Factories Muons, Inc.

2. Rol Johnson 6/22/2005 NuFact05 Plenary 2 Muons, Inc. SBIR/STTR Collaboration: (Small Business Innovation Research grants) Fermilab; Fermilab; Victor Yarba, Chuck Ankenbrandt, Emanuela Barzi, Licia del Frate, Ivan Gonin, Timer Khabiboulline, Al Moretti, Dave Neuffer*, Milorad Popovic*, Gennady Romanov, Daniele TurrioniVictor Yarba, Chuck Ankenbrandt, Emanuela Barzi, Licia del Frate, Ivan Gonin, Timer Khabiboulline, Al Moretti, Dave Neuffer*, Milorad Popovic*, Gennady Romanov, Daniele Turrioni IIT; IIT; Dan Kaplan*, Katsuya YoneharaDan Kaplan*, Katsuya Yonehara JLab; JLab; Slava Derbenev, Alex Bogacz*, Kevin Beard, Yu-Chiu ChaoSlava Derbenev, Alex Bogacz*, Kevin Beard, Yu-Chiu Chao Muons, Inc.; Muons, Inc.; Rolland Johnson*, Mohammad Alsharo’a, Pierrick Hanlet, Bob Hartline, Moyses Kuchnir, Kevin Paul*, Tom RobertsRolland Johnson*, Mohammad Alsharo’a, Pierrick Hanlet, Bob Hartline, Moyses Kuchnir, Kevin Paul*, Tom Roberts Underlined are 6 accelerator physicists in training, supported by SBIR/STTR grants Underlined are 6 accelerator physicists in training, supported by SBIR/STTR grants * present at this workshop * present at this workshop

3. Rol Johnson 6/22/2005 NuFact05 Plenary 3 5 TeV     Modified Livingston Plot taken from: W. K. H. Panofsky and M. Breidenbach, Rev. Mod. Phys. 71, s121-s132 (1999) The Goal: Back to the Livingston Plot

4. Rol Johnson 6/22/2005NuFact05 Plenary4 5 TeV ~ SSC energy reach ~5 X 2.5 km footprint Affordable LC length, includes ILC people, ideas High L from small emittance! 1/10 fewer muons than originally imagined: a) easier p driver, targetry b) less detector background c) less site boundary radiation

5. Rol Johnson 6/22/2005NuFact05 Plenary5 Principle of Ionization Cooling Each particle loses momentum by ionizing a low-Z absorber Only the longitudinal momentum is restored by RF cavities The angular divergence is reduced until limited by multiple scattering Successive applications of this principle with clever variations leads to smaller emittances for high Luminosity with fewer muons

6. Rol Johnson 6/22/2005NuFact05 Plenary6 Muon Collider Emittances and Luminosities After: –Precooling –Basic HCC 6D –Parametric-resonance IC –Reverse Emittance Exchange ε N tr ε N long. 20,000µm10,000 µm 200 µm 100 µm 25 µm 100 µm 2µm 2 cm At 2.5 TeV 20 Hz Operation:

7. Rol Johnson 6/22/2005NuFact05 Plenary7 Idea #1: RF Cavities with Pressurized H 2 Dense GH 2 suppresses high-voltage breakdown –Small MFP inhibits avalanches (Paschen’s Law) Gas acts as an energy absorber –Needed for ionization cooling Only works for muons –No strong interaction scattering like protons –More massive than electrons so no showers R. P. Johnson et al. invited talk at LINAC2004, http://www.muonsinc.com/TU203.pdfhttp://www.muonsinc.com/TU203.pdf Pierrick M. Hanlet et al., Studies of RF Breakdown of Metals in Dense Gases, PAC05 Kevin Paul et al., Simultaneous bunching and precooling muon beams with gas-filled RF cavities, PAC05 Mohammad Alsharo'a et al., Beryllium RF Windows for Gaseous Cavities for Muon Acceleration, PAC05 Also see WG3 talks by D. Cline, S. Kahn, and A. Klier on ring coolers for other use of ideas 1 and 2

8. Rol Johnson 6/22/2005NuFact05 Plenary8 Lab G Results, Molybdenum Electrode Linear Paschen Gas Breakdown Region Metallic Surface Breakdown Region Waveguide Breakdown Hydrogen Helium Fast conditioning: 3 h from 70 to 80 MV/m

9. Rol Johnson 6/22/2005NuFact05 Plenary9 Idea #2: Continuous Energy Absorber for Emittance Exchange and 6d Cooling Ionization Cooling is only transverse. To get 6D cooling, emittance exchange between transverse and longitudinal coordinates is needed. In figure 2, positive dispersion gives higher energy muons larger energy loss due to their longer path length in a low-Z absorber.

10. Rol Johnson 6/22/2005NuFact05 Plenary10 Idea #3: six dimensional Cooling with HCC and continuous absorber Helical cooling channel (HCC) –Solenoidal plus transverse helical dipole and quadrupole fields –Helical dipoles known from Siberian Snakes – z-independent Hamiltonian Derbenev & Johnson, Theory of HCC, April/05 PRST-AB

11. Rol Johnson 6/22/2005NuFact05 Plenary11 Photograph of a helical coil for the AGS Snake 11” diameter helical dipole: we want ~2.5 x larger bore

12. Rol Johnson 6/22/2005NuFact05 Plenary12 Due to b Due to B Motion due to b + B Magnet coils Helical Cooling Channel. Derbenev invention of combination of Solenoidal and helical dipole fields for muon cooling with emittance exchange and large acceptance. Well-suited to continuous absorber.

13. Rol Johnson 6/22/2005NuFact05 Plenary13 G4BL 10 m helical cooling channel RF Cavities displaced transversely 4 Cavities for each 1m-helix period B_=3.5 T =1.01 T B’_helical_quad=0.639 T/m B_solenoid=3.5 T B_helical_dipole=1.01 T B’_helical_quad=0.639 T/m

14. Rol Johnson 6/22/2005NuFact05 Plenary14 G4BL End view of 200MeV HCC Radially offset RF cavities Beam particles (blue) oscillating about the periodic orbit (white)

15. Rol Johnson 6/22/2005NuFact05 Plenary15 HCC simulations w/ GEANT4 (red) and ICOOL (blue) 6D Cooling factor ~5000 Katsuya Yonehara, et al., Simulations of a Gas-Filled Helical Cooling Channel, PAC05

16. Rol Johnson 6/22/2005NuFact05 Plenary16 Idea #4: HCC with Z-dependent fields 40 m evacuated helical magnet pion decay channel followed by a 5 m liquid hydrogen HCC (no RF)

17. Rol Johnson 6/22/2005NuFact05 Plenary17 5 m Precooler becomes MANX New Invention: HCC with fields that decrease with momentum. Here the beam decelerates in liquid hydrogen (white region) while the fields diminish accordingly.

18. Rol Johnson 6/22/2005NuFact05 Plenary18 G4BL Precooler Simulation Equal decrement case. ~x1.7 in each direction. Total 6D emittance reduction ~factor of 5.5 Note this requires serious magnets: ~10 T at conductor for 300 to 100 MeV/c deceleration

19. Rol Johnson 6/22/2005NuFact05 Plenary19 Idea #5: MANX 6-d demonstration experiment Muon Collider And Neutrino Factory eXperiment To Demonstrate –Longitudinal cooling –6D cooling in cont. absorber –Prototype precooler –New technology HCC HTS Thomas J. Roberts et al., A Muon Cooling Demonstration Experiment, PAC05

20. Rol Johnson 6/22/2005NuFact05 Plenary20 G4BL MANX with MICE spectrometers

21. Rol Johnson 6/22/2005NuFact05 Plenary21 Muon Trajectories in 3-m MANX

22. Rol Johnson 6/22/2005NuFact05 Plenary22 Phase I Fermilab TD Measurements Fig. 9. Comparison of the engineering critical current density, J E, at 14 K as a function of magnetic field between BSCCO-2223 tape and RRP Nb 3 Sn round wire. Licia Del Frate et al., Novel Muon Cooling Channels Using Hydrogen Refrigeration and HT Superconductor, PAC05

23. Rol Johnson 6/22/2005NuFact05 Plenary23 MANX/Precooler H2 or He Cryostat Figure XI.2. Latest iteration of 5 m MANX cryostat schematic.

24. Rol Johnson 6/22/2005NuFact05 Plenary24 Idea #6: Parametric-resonance Ionization Cooling (PIC) Derbenev: 6D cooling allows new IC technique PIC Idea: –Excite parametric resonance (in linac or ring) Like vertical rigid pendulum or ½-integer extraction Use xx’=const to reduce x, increase x’ –Use IC to reduce x’ –Detuning issues being addressed –chromatic aberration example Yaroslav Derbenev et al., Ionization Cooling Using a Parametric Resonance, PAC05 Kevin Beard et al., Simulations of Parametric-resonance IC…, PAC05 x

25. Rol Johnson 6/22/2005NuFact05 Plenary25 Transverse PIC schematic Conceptual diagram of a beam cooling channel in which hyperbolic trajectories are generated in transverse phase space by perturbing the beam at the betatron frequency, a parameter of the beam oscillatory behavior. Neither the focusing magnets that generate the betatron oscillations nor the RF cavities that replace the energy lost in the absorbers are shown in the diagram. The longitudinal scheme is more complex.

26. Rol Johnson 6/22/2005NuFact05 Plenary26 Beta functions and phases for the solenoid triplet cell. Thin absorbers are placed at the two central focal points. In the simulations for FIG 2 the lost energy is simply replaced at the absorbers. For FIG 3, 400 MHz RF cavities shown as blue bars replace the lost energy and provide synchrotron motion. SEE BOGACZ TALK!

27. Rol Johnson 6/22/2005NuFact05 Plenary27 Openinventor display from the G4Beamline simulation program showing the cell being modeled. The orange cylinders are solenoids as described above and the green cylinder is a solenoid of opposite polarity. The red cylinders represent 400 MHz RF cavities, the cyan disks are the energy absorbers, the large gray disks represent virtual detectors, and the green and red lines at the left end are the horizontal and vertical axes. The same G4Beamline view as above but with transparent beam line elements so that the muon trajectories can be seen. Detuning compensation schemes are being developed.

28. Rol Johnson 6/22/2005NuFact05 Plenary28 x x’ Dp/p s

29. Rol Johnson 6/22/2005NuFact05 Plenary29 Idea #7: Reverse Emittance Exchange At 2.5 TeV/c, Δp/p reduced by >1000. Bunch is then much shorter than needed to match IP beta function Use wedge absorber to reduce transverse beam dimensions (increasing Luminosity) while increasing Δp/p until bunch length matches IP Subject of new STTR grant

30. Rol Johnson 6/22/2005NuFact05 Plenary30 Incident Muon Beam Evacuated Dipole Wedge Abs Evacuated Dipole Wedge Abs Incident Muon Beam Figure 1. Conceptual diagram of the usual mechanism for reducing the energy spread in a muon beam by emittance exchange. An incident beam with small transverse emittance but large momentum spread (indicated by black arrows) enters a dipole magnetic field. The dispersion of the beam generated by the dipole magnet creates a momentum-position correlation at a wedge- shaped absorber. Higher momentum particles pass through the thicker part of the wedge and suffer greater ionization energy loss. Thus the beam becomes more monoenergetic. The transverse emittance has increased while the longitudinal emittance has diminished. Figure 2. Conceptual diagram of the new mechanism for reducing the transverse emittance of a muon beam by reverse emittance exchange. An incident beam with large transverse emittance but small momentum spread passes through a wedge absorber creating a momentum-position correlation at the entrance to a dipole field. The trajectories of the particles through the field can then be brought to a parallel focus at the exit of the magnet. Thus the transverse emittance has decreased while the longitudinal emittance has increased. Figure 1. Emittance Exchange Figure 2. Reverse Emittance Exchange

31. Rol Johnson 6/22/2005NuFact05 Plenary31 Seven New Ideas for Bright Beams for High Luminosity Muon Colliders supported by SBIR/STTR grants H 2 -Pressurized RF Cavities Continuous Absorber for Emittance Exchange Helical Cooling Channel Z-dependent HCC MANX 6d Cooling Demo Parametric-resonance Ionization Cooling Reverse Emittance Exchange If we succeed to develop these ideas, an Energy Frontier Muon Collider will become a compelling option for High Energy Physics! (The first five ideas can be used in Neutrino Factory designs.)

32. Rol Johnson 6/22/2005NuFact05 Plenary32 Challenges for Muon Colliders Extreme 6D muon cooling essential –Need simulations and demos, more ideas Acceleration –Can use ILC technology with recirculation –A good case for collaboration (10xE COM at half the cost?) –Mitigation of decay electrons Storage Ring/detectors –Low beta designs, exploit symmetry for multiple IPs –Integrate detectors with IP designs, solve e backgrounds –Understand neutrino-induced site boundary radiation