A. Bross MICE CM17 February 2007 1 MuCool RF Program 805 and 201 MHz Studies

A. Bross MICE CM17 February 2007 1

MuCool RF Program

805 and 201 MHz Studies


RF Cavity R and D

ANL/FNAL/IIT/LBNL/UMiss/Cockcroft


MuCool Test Area

Facility to test all components of cooling channel (not a test of ionization cooling)

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

p/pulse @15 Hz – 2.4 X 1014 p/s– 600 W into 35 cm LH2 absorber @ 400 MeV

RF power from Linac (201 and 805 MHz test stands) Waveguides pipe power to MTA


MTA Hall


MTA Hall Instrumentation

805

201CsI

Plastic Scintillator

Magnet

Chipmunk


Fundamental Focus Of RF R&D

Study the limits on Accelerating Gradient in NCRF cavities in magnetic field

However We believe that the

behavior of RF systems in general can be accurately described (predicted) by

Tensile strength of the material(s) used in the cavity fabrication (T)

Local surface field enhancements (eq)

Esurf = 2T//eq

This applies to all accelerating structures

In SC structures local heating becomes problem first

Follows universal curve


805 MHz

Data seem to follow universal curve

Max stable gradient degrades quickly with B field

Remeasured Same results Does not condition

Gra

dien

t in

MV/

m

Peak Magnetic Field in T at the Window


First RF 805 MHz Commissioning without

Magnetic Field Last MarchRadation Mon.#1 vs Gradient

y = 3E-22x16.246

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25 30 35

Gradient in MV/m

Rad

iatio

n in

mR

em/h

r

+ Time


First Radiation Measurement with Magnetic Field compared to No Field Data

Rad Mon #1 vs Grad with 2.5 justa-positioned with no Field

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35

Grad mV/m

Rad

iatio

n m

Rem

/hr 2.5 T Line

Lines Without Magnetic Field

March 06, Results.

Safe E Field Limit ~ 16MV/m Detector Distance=1.34 m


Nov. 06 Results: Electric field limit at 2.5 T in the LBLSingle Cell Cavity with Curve Be Windows coated with

TiN

0

5

10

15

20

25

30

35

40

45

12 14 16 18 20 22 24 26 28

RF Commissioning with Mag Field at 2.5 T

Pre RF Commissioning without Mag Field

Nov. 06 Results:Safe E field Limit ~16 MV/mDetector Distance=2.73 m Acccounts for scale


Latest Electric field limit Data at 2.5 T and 1.25 T in the LBLSingle Cell Cavity with Curve Be Windows

coated with TiN

0102030405060708090

13 15 17 19 21 23 25 27

Gradient MV/m

Rad

iatio

n m

R/H

r

Asymptotic Gradient limit line at 1.25 T

2.5 T Data

RF Conditioning without Magnetic Field

The Asymptotic limit line shown indicates the continuous Gradient sparking limit. In all the cases studied including Lab G this line as predicted the Gradient Limit for the cases under Study.

For the 1.25 T case the Save operating limit has been shown to be

20 MV/m

1.25 T Data


Comparison of Lab G Results with the MTA Data

Safe Operating Gradient Limit vs Magnetic Field Level at Window for the three different

Coil modes

40403736

3432.431.73128.8

26.7426.425.922

404037.663535.2

3028.527.327

4040

25.7523.2522.521.520.9

16.5 15 13.5

0

5

10

15

20

25

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35

40

45

0 1 2 3 4 5Peak Magnectic Field in T at the Window

Elec

tric

Gra

dien

t in

MV/

m

(Solenoid)Yellow

(Opposing) Red

(Single Coil)Black Diamond

MTA Result ~ 16 MV/mMTA 1.25 T Result Jan. 07


805 MHz Imaging


Next 805 MHz study - Buttons

Button test Evaluate various materials and

coatings Quick Change over


RF R&D – 201 MHz Cavity Design

The 201 MHz Cavity is now operating New data on x-ray backgrounds will be presented


X-Ray Detectors

#16: NaI crystal (1.5” diameter × 2”), upstream of 201 cavity #8: large thick scintillator paddle,

upstream of 201 cavity similar to MICE TOF(14” × 14.5” × 0.5”)


Procedures X-ray background measurements

Recording x-ray events for 1000 rf pulses Creating electronic gates to record

x-ray events at rf envelope during fill, flattop, decay and total range of rf pulse. RF pulse length ~ 100-μs

X-ray energy spectrum measurements

The histogram memory HM413 was calibrated with Co60 source

HM413 histogram memory was used to histogram the signals from AD413A ADC

Note: there is cosmic-ray background for all the measurements

1.17MeV peak


X-Ray Background Measurement of the 201-MHz cavity

Data taken in Dec. 2006 and Jan. 2007 with superconducting solenoid off The counting rates have been measured as a function of rf gradients. In

comparison with the x-ray intensity, the cosmic background is negligible. For MICE, accelerating gradient is 8MV/m limited by rf source

MICE gradient


Multipactoring Study

─ The impact of an electron to a surface can, depending on its energy and angle, release one or more secondary electrons into the vacuum.

─ These electrons can then be accelerated by the RF fields and impact with the same or another surface. Should the impact energies, number of electrons released and timing of the impacts be such that a sustained multiplication of the number of electrons occurs, the phenomenon can grow exponentially and may lead to operational problems of the RF system such as damage of RF components or loss/distortion of the RF signal.

Multipactoring is an effect that occurs when the Multipactoring is an effect that occurs when the electrons accelerated by RF fields are resonantly electrons accelerated by RF fields are resonantly enhanced via an electron avalanche caused by enhanced via an electron avalanche caused by secondary electron emissionsecondary electron emission


Multipactoring?

Possible multipactoring effects at some gradients, e.g., ~ 6.8MV/m in 201MHz cavity

There may be a very weak multipactoring effect. But too weak to distort rf field and produce huge ripples like above.

Multipactoring?

Typical multipactoring waveform pattern observed at

the 805 MHz cavity at MTA


Energy Spectrum Measurement of the 201MHz cavity

At 8-MV/m, the total counts recorded during 1000 rf pulses: #8: ~ 30,000; #16: ~ 21,000


X-Ray Background Measurement of the 805-MHz Cavity

When the rf gradient is higher than ~ 13-MV/m, the counting rates increase significantly (over 1 million/s) the NaI detector is not able to keep up and saturated. The counting rate is not accurate anymore, nor is the energy spectrum.

Cosmic background

x-ray

saturated


201 MHz Cavity Status

The 201 MHz Cavity is back up ready for operation We had a short in the 4” coax feeds to the couplers

The problem seemed to stem from the fact that parts from multiple vendors where used in the 4” coax run

Power coupler Straight sections Elbows

At the interfaces between parts from different vendors, the fit-up was not ideal

Inner conductor specifications seemed to vary This has now been fixed In addition we will be using pressurized (12 pisg) SF6

in the 4” coax run as the insulating gas instead of air


201 Coax Post-Mortem



High Pressure H2 Filled Cavity WorkMuon’s Inc

High Pressure Test Cell Study breakdown

properties of materials in H2

Run in B field No degradation in M.S.G. up

to 3.5T

Documents

A. Bross MICE CM17 February 2007 1 MuCool RF Program 805 and 201 MHz Studies