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RF Phase Shifter R&D

Proton Driver Review

March 15, 2005

T. Barrak, B. Foster, I. Gonin, M. Huening, V. Kashikhin, T. Khabiboulinne, A. Makarov, A. Moretti, P. Prieto, J. Santucci, N. Soliak, D. Sun, J. Volk, D. Wildman,

and

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RF Phase Shifter R&D

• Concept of phase & amplitude regulation

• Performance requirements

• Types of phase shifters and known experience

• High power test configuration and results

• Conclusion

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PD Linac: RF Power Distribution

One klystron feeds many cavities. For each cavity, fast change of amplitude and phase of input RF power is required.

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Amplitude and Phase (IQ) Modulator

cos0 jeEE

sin0 )2/(jeEE

= (1+2)/2

= (2-1)/2

1 2

Yttrium Iron Garnet

Ferrite Shifters can be built based on:

• Coaxial line,

• Strip-line,

• Waveguide

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Examples of Phase Shifters

L band (1.2 – 1.4 GHz)

350 kW peak power

Field Range 800 – 1500 Oe

Phase shift - 600°

Insertion loss - 0.2 dB

Coaxial Device, 1968

Strip-line-based design, AFT for CERN, ~ 2004

352 MHz

250 kW peak power

25% duty cycle

130º phase shift

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Examples of Phase Shifters

Waveguide-based device, Yoon Kang (ANL) for SNS ~ 2000

805 MHz

500 kW peak power

8% duty cycle

0.15 dB insertion loss

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Phase Control Simulations

Frequency follows that of the cavity

Cavity RF phase close to nominal

Phase Shifter works hard

Detailed simulation (M. Huening, EPAC-2004) shows that 200 sec response time is required.

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Performance Requirements

Frequency: 1300 MHz ± 1 MHz

Phase Change: ± 45°

RF Power Ratings: 550 kW Peak, 1.5 ms, 10 Hz

550 kW Peak, 4.5 ms, 3.3 Hz

Insertion Loss: less than 0.2 dB

Response time: time constant ~ 30 s

Flange: WR-650

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Approaching the Problem

1. Develop and test waveguide-based phase shifter;

2. Test the coaxial phase shifter available at FNAL

3. Work with a vendor to build an I/Q modulator

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Waveguide Phase Shifter

Main design issues:

• High power operation

• Heat management

• Tuning range

• Response time

CoreCoil

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Phase Shifter Mockup Low Level RF Measurements

Results of the low level RF measurements are in a good agreement with modeling (HFSS)

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High Power Test

A0 1300 MHz Klystron

T = 250 µsec

F = 5 Hz

Existing A0 interface was used for testing

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High Power Test

Two methods of phase measurements:

1. Oscilloscope measurements

2. Using available IQ modulator

Available phase zone is limited by sparking that develops near the resonance frequencies

Max Power - 2000 kW (req. 600 kW)

Phase shift - ~ 80° (req. 90° )

SF6 added

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Further Developments

1. Refining RF design

2. Fast phase shifter prototyping

3. IQ modulator prototyping

Anti-Parallel Bias Field

Parallel Bias Field

-2.0

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

1100 1120 1140 1160 1180 1200 1220 1240 1260 1280 1300 1320 1340 1360 1380 1400 1420 1440 1460 1480 1500F, MHz

20Lo

g(S1

1), d

B

17.5mm 1100 Oe -1110 Oe

17.5mm 1089 Oe -1111 Oe

17.5mm 1100 Oe -1100 Oe shift 1mm both

17.5mm 1080 Oe -1120 Oe shift 1mm both

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Coaxial Phase Shifter

•Coax design is preferred at 325MHz• In-house design tested to 660kW at 1300 MHz• Tested at 250 kW at Argonne with APS 352MHz Klystron • Fast coil and flux return should respond in ~50us

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Advanced Ferrite Technology GmbH (AFT)

Products:

High Power CirculatorsFast Ferrite TunerFast High Power Phase ShifterHybrid Tuner SystemsFerrite MaterialElectrical Power Suppliesfor high power inductive loads

The IQ modulator from AFT is expected in May:

1 Magic Tee; 1 straight waveguide section; 2 waveguide - coax transition; 2 FFT´s directly connecting to the transition; 1 control unit for setting phase and amplitude and feedback loop; 1 dual directional coupler for amplitude control; 1 arc detection system.

Power supply will be provided by FNAL

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Conclusion

1. The prototype of a waveguide-based, 1.3 GHz phase shifter shows excellent maximal power and acceptable phase shift performance.

2. Coaxial phase shifter meets peak power and phase shift requirements both at 1300 MHz and 325 MHz.

3. Commercial prototype of an I/Q modulator due in spring.

4. Average power testing, reaction time testing, and IQ modulator modeling should be the next steps of the R&D

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Phase Shifter Development Line

• Make low level calibration measurements using “as received” YIG blocks and a large gap dipole magnet

• Make steel magnet core and copper waveguide;

• Shape YIG block as modeling requires;

• Make low level RF measurements;

• Make high power measurements;

• Investigate ways to improve performance

• Make a combination “permanent magnet – high frequency winding” bias magnetic system with ferrite core

• Make a waveguide transparent for high frequency magnetic-field

• Make low level a.c. measurements to measure response time

• Work on a full-scale device design and test

DONE

Ongoing R&D

Engineering