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SPL11

A magnetron solution for proton drivers

Amos Dexter

Simulation Using Tech-X’s VORPAL e.m. code

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SPL11

Collaborations

Lancaster Richard Carter, Graeme Burt, Ben Hall, Chris Lingwood

JLab Haipeng Wang, Robert Rimmer

CEERI Shivendra Maurya, VVP Singh, Vishnu Srivastava

TechX Jonathan Smith

CERN ?

ESS ?

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SPL11

The Reflection Amplifier

J. Kline “The magnetron as a negative-resistance amplifier,”IRE Transactions on Electron Devices, vol. ED-8, Nov 1961

H.L. Thal and R.G. Lock, “Locking of magnetrons by an injected r.f. signal”,IEEE Trans. MTT, vol. 13, 1965

• Linacs require accurate phase control

• Phase control requires an amplifier

• Magnetrons can be operated as reflection amplifiers Cavity

Injection Source

Magnetron

Circulator

Load

Compared to Klystrons, in general Magnetrons

- are smaller - more efficient - can use permanent magnets (at 704 MHz) - utilise lower d.c. voltage but higher current - are easier to manufacture

Consequently they are much cheaper topurchase and operate

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SPL11

Proof of principle

Demonstration of CW 2.45 GHz magnetron driving a specially manufactured superconducting cavity in a VTF at JLab and the control of phase in the presence of microphonics was successful.

1W Amplifier

Agilent E4428 signal generator providing 2.45 GHz

Load 2

Load 3

High Voltage Transformer

42 kHz Chopper

Pulse Width Modulator SG 2525

Loop Coupler

Stub Tuner 1

Circulator 3

Circulator 2

Double Balance Mixer

LP Filter 8 kHz cut-off

1.2 kW Power Supply

300 V DC +5% 120 Hz ripple

2.45 GHz Panasonic 2M137 1.2 kW

Magnetron

Loop Coupler

Stub Tuner 2

Oscilloscope

Load

Oscilloscope

÷ 2

ADCDACIQ Modulator(Amplitude &

phase shifter)

÷ 2

DAC

Digital Signal Processor

Digital Phase DetectorHMC439

Phase shifter

Spectrum Analyzer 1

Phase shifter

Control voltage

Spectrum Analyzer 2

Cathode heater control

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SPL11

SCRF cavity powered with magnetron

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-500 -250 0 250 500Frequency offset (Hz)

Po

wer

sp

ectr

al d

ensi

ty (

dB

)

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-500 -250 0 250 500Frequency offset (Hz)

Po

wer

sp

ectr

al d

ensi

ty (

dB

)

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-500 -250 0 250 500Frequency offset (Hz)

Po

wer

sp

ectr

al d

ensi

ty (

dB

)

-15

-5

5

15

25

35

45

0.00 0.01 0.02 0.03 0.04 0.05

Time (seconds)

Cavity p

hase e

rro

r (d

eg

rees)

Control on

Control off

Injection but magnetron off

Injection +magnetron on

Injection +magnetron on +

control

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SPL11

Next Steps

• Development of a 704MHz Magnetron (440kW – 880kW )

Collaboration with CEERI, Pilani, India

• Procure standard modulator

Hope to use klystron modulator with different pulse transformer however rate of voltage rise is tightly defined. Need to deal with impedance change on start up. The CI have a suitable 3 MW magnetron modulator for short pulses up to 5 micro-seconds and could be used for characterisation

• Establish test station with Television IOT as the drive amplifier

Could be used for conditioning SPL and ESS components

• Understand locking characteristics of new magnetron

• Commission advanced modulator with in-pulse current control

• Establish minimum locking power

• Establish two magnetron test stand

• Develop LLRF for simultaneous phase and amplitude control

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Layout using one magnetron per cavity

Permits fast phase control but only slow, full range amplitude control

LLRF

880 kW Magnetron

4 Port Circulator

Load

Slow tuner

60 kW IOT

Standard Modulator

Pulse to pulse amplitude can

be varied

Cavity

~ -13 dB to -17 dB needed for locking i.e. between 18 kW and 44kW hence between 42 kW and 16 kW available for fast amplitude control

Could fill cavity with IOT then pulse magnetron when beam arrives

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SPL11

Layout using two magnetrons per cavity

Permits fast full range phase and amplitude control

Cavity

~ -30 dB needed for

locking

Load

440 W

Advanced Modulator

Fast magnetron

tune by varying

output current440 W

440 kW Magnetron

440 kW Magnetron

Advanced Modulator

Fast magnetron

tune by varying

output current

LLRF

output of magnetron 1

output of magnetron

2

Phasor diagram

combiner / magic tee

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SPL11

Reflection Amplifier Controllability

Magnetron frequency and output vary

together as a consequence of

1. Varying the magnetic field

2. Varying the anode current (pushing)

3. Varying the reflected power (pulling)

1. Phase of output follows the phase of the input signal

2. Phase shift through magnetron depends on difference between input frequency and the magnetrons natural frequency

3. Output power has minimal dependence on input signal power

4. Phase shift through magnetron depends on input signal power

5. There is a time constant associated with the output phase following the input phase

1 2 3 4 5

Anode Current Amps

10.0 kV

10.5 kV

11.0 kV

11.5 kV

12.0 kV

AnodeVoltage

Power supply load

line

916MHz915MHz10kW 20kW 30kW 40kW

2.70A

3.00A

2.85A

2.92A

2.78A

Magnetic field coil current

2 3 4 6

900 W

800 W700 W

towardsmagnetron

VSWR

+5MHz

+2.5MHz

-2.5MHz

-5MHz

Moding

+0MHz

Arcing

0o

270o

180o

90o

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SPL11

CEERI Collaboration

Dr Shivendra Maurya of the Microwave Tube Division, CEERI, PILANI, India visited Lancaster University from 1st August to 31st November to start work on the design of a suitable magnetron.

This visit has been funded by the Royal Academy of Engineering.

If there is sufficient interest CEERI will seek funding to manufacture the magnetron. CEERI already manufacture a range of tubes mainly for use in India.

S-band, 3.1 MW Pulse Tunable Magnetron for Accelerator

5 MW (pk), 5kW(avg) S-band

Klystron as RF amplifier for

injector microtron in

Synchrotron Radiation Source

at RRCAT, Indore

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Specification of initial device

Frequency 704 MHzPower 200 kW to 1 MWPulse length 5s to 5 ms (for max power)Max average power 100 kWEfficiency > 90% above 500 kWMagnet NyFeB (< 0.5 T)External Q ~ 50 (for ease of locking)Mechanical Tunability ~ 5 MHzCathode heating indirect and controllable

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Approximate Calculations

Power output W 5.26E+05 1.00E+06 GivenOverall efficiency target 0.9066 0.9210 AssumedDC power W 5.80E+05 1.09E+06 DerivedDC impedance Ohms 1615 1615 GuessedAnode voltage 30611 41876 DerivedAnode current 18.954 25.930 DerivedCathode plus circuit losses 4.00% 4.00% Estimatedelectronic efficiency 94.66% 96.10% DerivedV anode over V threshold 1.25 1.25 AssumedV threshold V 24488 33501 DerivedModified Slater factor 1.96 2 AssumedNumber of Vanes 14 14 AssumedAnode radius m 0.02400 0.02401 CalculatedCathode radius m 0.01775 0.01774 CalculatedAnode height m 0.05536 0.05536 AssumedCathode current density A/m^2 3070 4202 DerivedElectric field V/m 9.79E+06 1.34E+07 DerivedVoltage field product kV/mm^2 299.6 559.8 DerivedB T 0.30477 0.41331 Calculated

Using standard theory one can estimate Magnetic field, anode and cathode radii from requirement data (frequency 704 MHz, efficiency >90% and power

Should be able to use same block for efficient generation at both the 500 KW and 1 MW level

o

oe B5.1B

B5.0B

1B

B2

V

V

oo

th

2a

2rf

o rNe

m2V

2ac

rfo

rr1

1

Ne

m4B

cca

caF V

V1N

rr

rrS

2

ooc B

BVV

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SPL11

Expected operating range

VORPAL simulations

Short circuit regime

Threshold for moding

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VORPAL Predictions at 30 kV

Take

B = 0.3 T,

Va = 32 kV,

Ic = 60 A

Predict

Ianode = 19 A,

Efficiency = 92%,

Power = 560 kW

Z = 1684

Anode current (A)

Cathode voltage (V)

Output power (W)

time (s)

time (s)

time (s)

Volts

Amps

Watts

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Moding Issues

Voltage in magnetron

time (s)

time (s)

time (s)

Volts

Volts

FFT (dB)

Excitation in the mode at 1060 MHz might be a problem.

We think the coarse mesh or other issues with the simulation might exacerbate the issue.

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SPL11

MWS modes

mode at 702 MHz

mode at 1060 MHz mode at 1063 MHz

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SPL11-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

-0.030 -0.025 -0.020 -0.015 -0.010 -0.005 0.000 0.005 0.010 0.015 0.020 0.025 0.030

Efficient Orbits

An efficient orbit should have no loop

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SPL11

Magnetron Size

Magnets

dg

dmhm

704 MHz

dg ~ 360 mm

dm ~ 165 mm

hm ~ 650 mm

cost £8000

air cooling input for dome

water cooling for

anode

air cooling for cathode

If magnetron design is similar to industrial design with similar tolerances and can be made on same production line then cost may not be much more

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SPL11

High Efficiency Klystrons

• Design of high efficiency klystrons for ESS in collaboration with CLIC– Similar Klystrons (704.4 MHz, 1.5 MW, 70%

efficiency) allow synergetic activities with CLIC.– Focus on understanding of bunching process

and space charge in the output cavity.– Using evolutionary algorithms to improve

optimisation– New design concepts to achieve optimum beam

modulation– Single and Multiple beams investigated

Images courtesy of Thales Electron Devices