NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

201 MHz NC RF Cavity R&D for Muon Cooling Channels

Derun LiCenter for Beam Physics

International Neutrino Factory WorkshopWG-3, Frascati, Italy

June 21-26, 2005

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

Outline

• Introduction— Ionization cooling— Requirements of RF cavities for muon cooling

• RF cavity R&D activities— 805 MHz cavity805 MHz cavity— 201 MHz cavity

• Status of the prototype cavity• Be window R&D• RF Couplers

• Summary

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

Introduction

Ionization cooling principle

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

LH Absorbers

RF Cavities

dxdE

dxdE

dxdE

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

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 conductingRounded closed “pillbox” cavityRounded closed “pillbox” cavity

LargeLarge and and thinthin BeBe foils (low-Z) to terminate RF fields 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

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

NCRF Cavity R&D Activities

Experimental studies using an 805 MHz pillbox cavity with

demountable windows at MTA (Lab G), FNAL

Lab G Magnet (MTA)

805 MHz cavity inside

• 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?

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

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

Layout of water cooling lines on cavity

Cavity design concept

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

The 201 MHz Cavity Parameters

The cavity design parameters

—Frequency: 201.25 MHz— β = 0.87

—Shunt impedance (VT2/P): ~ 22 MΩ/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

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

The Cavity Fabrication

We have successfully developed extrudingtechnique for port pulling over e-beam joints

E-Beam Welding of Stiffener

Ring at J-Lab

Finished equator welding

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

The Cavity + Sub-components

Ceramic RF window Loop coupler Finished cavity port

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

EP at J-Lab

U-Shape Electrode

After 1st EP run last week (June 2005)

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

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

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

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

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

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

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

420 mm

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

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

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

RF Power

Two couplers

Load 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

Coupler Conditioning

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

Mucool Test Area (MTA)

– At high beam power• Designed to accommodate full Linac Beam• 1.6 X 1013

p/pulse @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

Facility to test all components of cooling channel, not ionization cooling

201-MHz

805-MHz

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

Eight 201 MHz Cavities for MICE

Two SC coupling Coils

Eight 201 MHz cavities

Power couplers

The 201 MHz prototype cavity is the baseline design for MICE

NCRF R&D of 201 MHz Cavity (D. Li, NuFact-2005, Frascati, Italy)

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