July 28, 2004K. Yonehara, NuFact'04 Osaka1 High pressure RF cavities for muon beam cooling Katsuya Yonehara Illinois Institute of Technology NuFact04 in Osaka 7/28/04

July 28, 2004K. Yonehara, NuFact'04 Osaka2 Muon accelerators Muon colliders (Energy frontier machine) –No limitation by synchrotron radiation Radiation (beam-strahlung) factor (m  /m e ) 2 ~ 40,000 –1/10 energy/footprint of proton colliders Energy of interaction is full energy of produced particle since  s are fundamental particles. Neutrino factories (Muon storage ring) –Exciting new physics

July 28, 2004K. Yonehara, NuFact'04 Osaka3 Six muon projects Promoted by Muons, Inc., July, 2004 High-pressure gaseous hydrogen RF cavity MANX (Muon collider And Neutrino factory eXperiment) 6-Dimensional helical cooling channel –see MuCoolNote0284 Hydrogen cryostat Phase ionization cooling Cryogenic pulsed power compressor See “ “ for below three items

July 28, 2004K. Yonehara, NuFact'04 Osaka4 Muon ionization cooling Step 1: Beam energy loss dE/dx in transverse and longitudinal directions Step 2: Longitudinal energy replaced by RF electric acceleration field # A strong solenoidal magnetic field is required to make a low  in cooling material. Cooling material Step 1 Step 2 This method is only available for muons. PyPy PzPz

July 28, 2004K. Yonehara, NuFact'04 Osaka5 Properties of gaseous hydrogen Best cooling material –Highest (X 0 dE/ds) 2 High heat capacity –Cools Be RF windows effectively Low critical temperature –33 K

July 28, 2004K. Yonehara, NuFact'04 Osaka6 Advantages of high pressure gaseous hydrogen in an RF cavity Dense GH 2 suppresses high-voltage breakdown –Small mean free path inhibits avalanches (Paschen’s law) Gas acts as an energy absorber –Needed for ionization cooling

July 28, 2004K. Yonehara, NuFact'04 Osaka7 Phase I research Build cryogenic HP RF test cell –Need special sealing technology on every joint (ex. RF feed line, pickup coil, etc) –Good pressure seal and RF seal Measure RF breakdown voltage vs. pressure –The data should follow Paschen’s law, relating breakdown voltage to gas density, over a range of temperatures, and pressures. –Compare helium and hydrogen.

July 28, 2004K. Yonehara, NuFact'04 Osaka8 Collaborators R. E. Hartline, R. P. Johnson, M. Kuchnir, T.J. Roberts Muons, Inc. C. M. Ankenbrandt, A. Moretti, M. Popovic Fermi National Accel. Lab M. Alsharo’a, D.M. Kaplan, K. Yonehara Illinois Institute of Tech.

July 28, 2004K. Yonehara, NuFact'04 Osaka9 HP RF cavity Electrode (“knob”) replaceable Metal sealing (use Aluminum gasket) RF feed line All surfaces are copper plated

July 28, 2004K. Yonehara, NuFact'04 Osaka10 Test Cell

July 28, 2004K. Yonehara, NuFact'04 Osaka11 Experiment

July 28, 2004K. Yonehara, NuFact'04 Osaka12 Frequency shift

July 28, 2004K. Yonehara, NuFact'04 Osaka13 11/19/03 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

July 28, 2004K. Yonehara, NuFact'04 Osaka14 Results 80 MV/m surface gradient achieved Fast conditioning (Last 15 MV/m in 3 h) Note that the resonant frequency diminishes with pressure since the dielectric constant depends on density. As the klystron was tuned to follow the cavity resonant frequency, a resonance in the wave guide caused breakdown before the power reached the cavity i.e. the dip in the previous plot.

July 28, 2004K. Yonehara, NuFact'04 Osaka15 Plan I: Observe breakdown Study metal surface breakdown –Change electrode material Cu, Mo, Cr, Be (ref. Perry Wilson) Optical approach –Use glass fiber optics Good transmission efficiency from UV to VIS region Insensitive to temperature –Use photo diode Good sensitivity from UV to VIS region Insensitive to magnetic field –Use C fiber ferrule for optical feedthrough Sealing test has been done under 1600 PSI GHe Yet to do the same test at cryogenic temperature

July 28, 2004K. Yonehara, NuFact'04 Osaka16 Plan I setup NPT-SWG1/8 C fiber ferrule Fiber optics (D 500 microns) Change electrodes materials

July 28, 2004K. Yonehara, NuFact'04 Osaka17 Plan II: Test with proton beam What is breakdown voltage with ionizing radiation? We expect; –Fast ion recombination in HP GH 2 Much shorter than the RF period –RF breakdown is suppressed Extrapolating from our measurement ~700 MV/m at one half of LH2 density

July 28, 2004K. Yonehara, NuFact'04 Osaka18 Hopes for HP RF cavity Higher gradients than with vacuum Less dependence on metallic surfaces –Dark currents, x-rays diminished –Very short conditioning times already seen Easier path to closed-cell RF design –Hydrogen cooling of Be windows Can be used for 6D cooling and acceleration –Homogeneous absorber concept –Implies HF for muon acceleration (1.6 GHz)

July 28, 2004K. Yonehara, NuFact'04 Osaka19 Present activities for HP RF Phase II project Studying RF breakdown with Cu, Mo, Cr, Be electrodes 50:85:112:194 (Perry Wilson) Planning Test Cell for Operation in the 5 Tesla solenoid at 1600 PSI (~ 110 atm) and 77K Working on MTA Beamline –Want radiation test of GH 2 RF in 2005 Constructing simple MTA beam line (reference; MuCoolNote0287, 0294)

July 28, 2004K. Yonehara, NuFact'04 Osaka20 MANX project This is a first project using the high pressure gaseous RF cavities Muons, Inc. are funding phase I

July 28, 2004K. Yonehara, NuFact'04 Osaka21 MANX is GH 2 version of MICE

July 28, 2004K. Yonehara, NuFact'04 Osaka22 Summary for HP GH 2 RF GH 2 an enabling technology for  machines –High gradient RF for less-expensive, more efficient beam cooling –Emittance exchange with homogeneous absorber 6D cooling makes Muon Collider possible –Maybe ionization cooling parametric resonances for higher luminosity 6D cooling for less expensive acceleration for Neutrino Factory

July 28, 2004K. Yonehara, NuFact'04 Osaka23 6-Dimensional helical cooling channel Design and feasible study of 6D HCC by using ICOOL and G4BL

July 28, 2004K. Yonehara, NuFact'04 Osaka24 Helix cooling channel B  couples with v z B z  couples with v  HPGH2 filled RF cavity Helix + Solenoid coils One segment

July 28, 2004K. Yonehara, NuFact'04 Osaka25 Helical Dipole Magnet Warm spin rotator for AGS ring at BNL

July 28, 2004K. Yonehara, NuFact'04 Osaka26 Simulation results in ICOOL 1 Reference orbit Particle orbit z x y Bx, By z

July 28, 2004K. Yonehara, NuFact'04 Osaka27 Simulation results in ICOOL No cooling material Multiple scattering on No multiple scattering transverse longitudinal 6-d N = 500 muons

July 28, 2004K. Yonehara, NuFact'04 Osaka28 Possible origin of RF off-phase 

July 28, 2004K. Yonehara, NuFact'04 Osaka29 Summary for 6D HCC Analytical investigation by Ya S. Derbenev and R.P. Johnson –Cooling factor: ~10 6 First cooling effects were observed in ICOOL –Cooling factor: >10 6 without multiple scattering – : ~20 with multiple scattering –Need tilting RF cavities Progress on G4BL –Install ICOOL helix field and tested –Test basic parameters (compare with ICOOL): dE/ds, Multiple scattering angle, range: a few % discrepancy