Measurements of RF properties of Novel Superconducting Materials

Jiquan Guo, Sami Tantawi, Charles

Yoneda, David Martin(SLAC)

Tsuyoshi Tajima(LANL)

Oct. 4, 2010

Sami Tantawi, Thinfilms for SRF

Outline

• Motivation• System description

– Overview– Cavity design

• Experiment results– Bulk Niobium– Thin film

• Summary

Sami Tantawi, Thinfilms for SRF

Motivation

• Test bed for SRF materials– Magnetic quenching field characterization

• Possibly higher than Nb’s 170-180mT• Different thin film or bulk sample

– Quick testing cycles with small samples – Able to explore higher Tc materials (MgB2)

– Surface resistance characterization

• Non-superconducting materials– RRR of Copper in different forms– Other materials

System overview

• Characterize surface impedance by measuring the Qs of a cavity

• Capable of low power(NWA) and high power(Klystron) measurements

• X-band compact design• Interchangeable flat cavity bottom, fits 2-3” diameter

samples• Cavity design maximizes H-field and minimizes E-field on

the sample surface• Can achieve ~360mT Hpeak with 50MW Klystron running

1.6µs flat pulses and Qe~320,000, Q0~320,000

Sami Tantawi, Thinfilms for SRF

Cavity Design

• High-Q hemispheric cavity under a TE013 like mode– Zero E-field on sample– Maximize H-field on the sample,

Hpeak on bottom is 2.5 times of peak on dome

– Maximize loss on the sample, 36% of cavity total

– No radial current on bottom

• Copper cavity body– No temperature transition or

quenching– Higher surface impedance– Coupling sensitive to iris radius

• Possible future Nb cavity body– More precise Rs characterization

Sami Tantawi, Thinfilms for SRF

High-Q cavity under TE013 like mode

Q0,4K=~224,000Q0,290K=~50,000(measured from bulk Cu samples)

Fres, design=~11.399GHzFres, 290K=~11.424GHzFres, 4K=~11.46GHz

Q0,4K=~342,000(Estimated for zero resistivity samples, using measured Cu sample results)

Sample R=0.95”

Tc~3.6µs(using Q value for copper at 4K)

Qe~310,000

H E

Sami Tantawi, Thinfilms for SRF

Cavity Assembly

Sami Tantawi, Thinfilms for SRF

System overviewMeasurement ports:Forward Power: 2 or 5Reflected power: 4 or 3Waveform measured by either a Peak Power Meter or a scope with mixersLow power NWA measurement: 6, 7, or 3

• Cryostat

• Waveguide to Klystron/NWA

1

2

3

4

Cavity

Klystron

10dB

45dB 45dB

5

6

55dB

7

Cryostat

Mode converter Bend

LoadSystem Diagram

AFGI

Q

TWT Klystron

Computer

Cavity

Load

LO

Scope

PPM

Temperature Monitor

Cavity heater power supply

Frequency Control

I/Q control

FWDRF

REFRF

T read/control

Load

Power trace

Amp and phase

LO

phase

Amplitude

Frequency tuning

Measurement Results: Bulk Nb, high power test

Sami Tantawi, Thinfilms for SRF

0

5000

1 104

1.5 104

2 104

2.5 104

0 2 4 6 8 10

Forward and reflected power traceS15-1, H~23mT

Reflected Forward

Pow

er (

W)

Time(s)

0

1 104

2 104

3 104

4 104

5 104

6 104

7 104

8 104

3 4 5 6 7 8 9 10

Reflected power tracesafter forward power turned off

at different power level

H~104mT, no quenchingH~153mT, quenched

Pow

er (W

)

Time(s)

Power traces of the high power test

Nb Measurements vs. Pulse Length and Repetition Rate

Sami Tantawi, Thinfilms for SRF

Sami Tantawi, Thinfilms for SRF

Gradual Quenching Theory

Measurement Results: Bulk Cu

Sami Tantawi, Thinfilms for SRF

5 104

1 105

1.5 105

2 105

2.5 105

0 50 100 150 200 250 300

SLAC Cu sampleLow power test result

Q0Q0

Temperature(K)

This reference Cu sample is used to estimate the surface impedance of the cavity body. It uses similar material as the body, and the same annealing process.

Measurement Results: Bulk Nb, low power test

Sami Tantawi, Thinfilms for SRF

FNAL bulk large grain Nb sampleSample surface impedance is estimated from the measured Q0 of the cavity with Nb sample and the measured copper surface impedance. Without magnetic shielding, the residual resistivity is high. After adding a magnetic shielding and 800˚C vacuum bake, surface impedance reduced by a factor of 3.

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 5 10 15 20 25 30

FNAL-Nb S15-1Estimated Rs

W/o shielding, before baking W/ shielding, before bakingW/ shielding, after baking

Rs

(Oh

m)

Temperature(K)

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

0 20 40 60 80 100

FNAL Nb S15-1measured Q

0

Before baking, w/o shieldingBefore baking, w/ shieldingAfter baking, w/ shielding

Q0

Temperature (K)

Measurement Results: Bulk Nb, high power test

Sami Tantawi, Thinfilms for SRF

FNAL bulk large grain Nb sampleThe residual resistivity is causing pulse heating and degrades the quenching field.Before magnetic shielding and baking, the sample start to quench at ~65mT with temperature rises ~5K.After shielding and baking, quenching starts at about 120mT when temperature rises ~3K.

1.1 105

1.2 105

1.3 105

1.4 105

1.5 105

1.6 105

1.7 105

1.8 105

0 20 40 60 80 100 120 140 160

FNAL Nb S15-1Q vs H, T=3K

w/ and w/o shielding/baking

Ql 04012010, no shielding, no bakingQl 09216010 with shielding, after baking

Qlo

ad

ed

Hpeak (mT)

Sami Tantawi, Thinfilms for SRF

Measurement results: 300nm MgB2 on Sapphire

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

4 105

0 5 10 15 20 25 30 35 40

300nm MgB2 thinfilm on SapphireQ vs T

H=10mT vs low power

Q0, H=10mTQ0, network analyzer

Q0

Temperature(K)

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

4 105

10 15 20 25 30

MgB2 thinfilm on SapphireQvsH

T=3K, 04082010

Q0Q0

Hpeak (mT)

300nm MgB2 thin film on Sapphire substrate, provided by LANL and deposited at STI.

Sami Tantawi, Thinfilms for SRF

Measurement results: MgB2/Al2O3/Nb

200nm MgB2/300nm Al2O3/Nb sample provided by LANL, Al2O3 coated at ANL, MgB2 coated at STI.

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

8 104

1 105

1.2 105

1.4 105

1.6 105

10 20 30 40 50 60 70

Q vs HMgB

2/Al

2O

3/Nb

T=3K, June 11, 2010

Q0

Qloaded

Q0

Qloa

ded

Hpeak (mT)

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

0 10 20 30 40 50

Q vs T for MgB2/Al

2O

3/Nb

Low power test(NWA) vs high power test(12mT)

Q0(NWA, 06112010)Q0(NWA, 06042010)Q0(H=12mT, 06102010)Q0(H=12mT, 06112010)

Q0

Temperature(K)

Sami Tantawi, Thinfilms for SRF

Summary

• Demonstrated a system which can precisely measure the quenching field of up to 300-400mT

• Magnetic shielding is crucial for Nb residual resistivity. At X-band, pulse heating from residual resistivity can easily degrade the quenching field.

• Precision of Rs measurement is currently at the level of 0.1mΩ. It can be improved with a separate Nb cavity.