201 MHz NC RF Cavity R

1
201 MHz NC RF Cavity RD for Muon Cooling
Channels

• Derun Li
• Center for Beam Physics
• International Neutrino Factory Workshop
• WG-3, Frascati, Italy
• June 21-26, 2005

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Outline

• Introduction
• Ionization cooling
• Requirements of RF cavities for muon cooling
• RF cavity RD activities
• 805 MHz cavity
• 201 MHz cavity
• Status of the prototype cavity
• Be window RD
• RF Couplers
• Summary

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Introduction

• Ionization cooling principle

LH Absorbers
RF Cavities

• Strong magnetic field to confine muon beams
• Lose energy in LH absorbers
• High gradient RF cavities to compensate for
  lost longitudinal energy

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RF Cavity for Muon Cooling

• Requirements
• Intense muon beams
• Have short lifetime and large phase space
• Interact weakly with matter
• Confined in focusing channels

• High gradients
• 17 MV/m at 201 MHz and 34 MV/m at 805 MHz
• Normal conducting
• Rounded closed pillbox cavity
• Large and thin Be foils (low-Z) to terminate RF
  fields
• High cavity shunt impedance
• Low peak surface field
• High accelerating efficiency with independent
  phase control
• Less RF power

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NCRF Cavity RD Activities

• Experimental studies using an 805 MHz pillbox
  cavity with demountable windows at MTA (Lab G),
  FNAL

• Achievable accelerating gradient is a function
  of external B
• Be windows withstand high field without surface
  damage
• How to interpolate the results to 201 MHz
  cavities?
• Does this apply to 201 MHz cavities?

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201 MHz Prototype Cavity

• Goal Design, build a 201-MHz cavity with large
  Be windows, and condition and operate it at 16
  MV/m in a few Tesla magnetic field
• Cavity and its sub-components
• Cavity body water cooling
• lines
• Four ports and flanges
• RF loop couplers
• Cavity support structure
• Cavity tuners
• Ceramic RF windows ( 4)
• Curved Be windows
• Possible LN temperature
• operation

Cavity design concept
Layout of water cooling lines on cavity
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The 201 MHz Cavity Parameters

• The cavity design parameters
• Frequency 201.25 MHz
• ß 0.87
• Shunt impedance (VT2/P) 22 M?/m
• Quality factor (Q0) 53,000
• Curved Be window with radius and thickness 21-cm
  and 0.38-mm
• Nominal parameters for cooling channels in a
  neutrino factory
• For up to 16 MV/m peak accelerating gradient
• Peak input RF power 4.6 MW per cavity (assuming
  85 of Q0 and 3 times filling time)
• Average power dissipation per cavity 8.4 kW
• Average power dissipation per Be window 100
  watts

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The Cavity Fabrication
Finished equator welding
E-Beam Welding of Stiffener Ring at J-Lab
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The Cavity Sub-components
Loop coupler
Ceramic RF window
Finished cavity port
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EP at J-Lab
After 1st EP run last week (June 2005)
U-Shape Electrode
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Current Status Near Term Plans

• Continue EP at J-Lab
• High pressure water rinsing
• Vacuum Assembly and base pressure measurement
• Packing and Shipping
• Couplers, RF probes, gauges and vacuum pump
  assembly at the MTA, FNAL
• Baking at the MTA, FNAL
• RF conditioning (Ti-N coated copper windows to
  start with) without magnetic field

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Curved Be Windows for 201 MHz Cavity

• Succeeded in two curved Be windows for the
  805-MHz cavity
• Placed purchase order of three Be windows for
  201-MHz cavity
• 0.38 mm thick, 420 mm diameter
• at Brush-Wellman (100 watts per window with
  ?T 55 degrees at nominal Study-II parameters)
• Window is formed by applying a die at elevated
  temperature
• Copper frame is brazed to Be window
• Be windows will be Ti-N coated

• Present a perfect conducting BC for RF.
• Min. scattering and mechanically strong

420 mm
420 mm diameter curved Be window for the 201 MHz
cavity formed at Brush-Wellman. The formed Be
foil is sandwiched (brazed) in two annular Cu
frames

• The curved Be window status
• warping (1st one)
• cracking (2nd) on edge, but usable
• Two good windows already
• To be Ti-N coated

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RF Coupler Design and Status

• Loop couplers at critical coupling
• Prototype coupling loop design uses standard
  off-the-shelf copper co-axial components
• Coupling loop has integrated cooling lines
• Two SNS style RF windows mfg. by Toshiba
• received (no cost to us !)
• Two couplers with RF windows are complete
• High power tested up to 600 kW in TW mode and
  2.4 MW (peak) in SW mode
• Ready to ship to MTA, FNAL
• Bellows connection required on MICE cooling
  channel (Study-II) for thermal and dimensional
  reasons

Ceramic RF window

Loop coupler
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Coupler Conditioning

• The two Couplers
• Conditioning started in the week of May 16, 2005
  at SNS
• Good vacuum low 10-8 T
• Achieved 600 kW in TW mode (matched load)
• Achieved 10 kW average power ( 9 kW average for
  nominal NF parameters)
• Achieved 2.4 MW peak power in SW mode (at
  variable short positions)
• Ceramic windows work fine in nearly two weeks of
  the RF conditioning

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Mucool Test Area (MTA)
805-MHz
201-MHz
Facility to test all components of cooling
channel, not ionization cooling

• At high beam power
• Designed to accommodate full Linac Beam
• 1.6 X 1013 p/pulse _at_15 Hz
• 2.4 X 1014 p/s
• RF power from Linac 201 and 805 MHz test stands
• Waveguides pipe power to MTA
• Clean room ordered
• On site assembly of windows

• Currently plan to operate either RF or LH2/H2
  tests, but not both simultaneously.
• 805 MHz experimental study
• will resume soon
• 201 MHz cavity expect to
• arrive next month

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Eight 201 MHz Cavities for MICE
Two SC coupling Coils
Power couplers
Eight 201 MHz cavities
The 201 MHz prototype cavity is the baseline
design for MICE
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Summary

• MTA is ready to accept high power RF test
  programs
• 805 MHz experimental programs will resume soon at
  MTA, FNAL
• 201 MHz prototype cavity progress well and expect
  to be shipped to MTA, FNAL for high power tests
  next month (July 2005)
• Significant progress on fabrication of curved Be
  windows
• RF couplers have been high power tested and ready
  for assembly at the MTA, FNAL
• MUCOOL 201 MHz cavity is the baseline design for
  MICE