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Design and Test of a Metamaterial Based
High Power Microwave Generator
Jason S. HummeltMassachusetts Institute of Technology-PSFC
Cambridge, MA USA
Muri Talk-March 4, 2016
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Outline
Introduction
Metamaterial design and simulations
Experimental results
Conclusion
#2
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#3
Beam Powered Metamaterial
Metamaterials with ε,μ < 0 can exhibit ‘reverse Cherenkov radiation’
Electron bunches form because of beam-wave synchronism (ve = vphase) AND
feedback mechanism
n>1, v>c n<1, v>c
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Experiment Goals
Design and test of S-band Backward Wave Oscillator Utilize a metamaterial interaction circuit
#4
Haimson Research
Electron Gun
Design Pout 5 MW
Frequency 2.4 GHz
Current 80 A
Voltage 500 kV
Pulse Length 1 μs
Experiment before installation on gun
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Outline
Introduction
Metamaterial design and simulations
Experimental results
Conclusion
#5
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Structure Design
New single CSRR structure fabricated Fully brazed structure eliminates slots
Slightly different dispersion/operation
frequency
MTM Design
f0 2.40 GHz
Period 10 mm
Thickness 3.125 mm
Power (CST Sim) 6 MW
#6
1 Period
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Cherenkov vs Anomalous Doppler
Cherenkov 𝜔 = 𝑘𝑧𝑣𝑧 Does not tune with B field
Anomalous Doppler 𝜔 = 𝑘𝑧𝑣𝑧 − Ω𝑐/𝛾 Tunes with B field
#7
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CST PIC Simulations
#8
Bz=900 G
Bz=700 G
Symmetric mode excited at high B
field (>800 G)
Antisymmetric mode excited at low
B field (<750 G)
Different particle orbits for each
mode excitation Antisymmetric: beam spirals
Symmetric: beam bunches axially
Antisymmetric has more efficient
electron energy loss
Antisymmetric
Symmetric
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Cold Test
#9
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Outline
Introduction
Metamaterial design and simulations
Experimental results
Conclusion
#10
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HPM Metamaterial Experiment
Lens
Electron Beam
SolenoidVacuum
Chamber
Viewport
Collector
Electric
Standoff
RF Load
#11
Bethe Hole Coupler
MTM Structure
CSRRs
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MTM Power
#12
Pout 2.3 MW
Frequency 2.39 GHz
Current 60 A
Voltage 400 kV
RF Pulse Length 300 ns
Magnetic Field 375 G
High power operation in antisymmetric
mode Only see high power for low magnetic
field
Interception on metamaterial structure
Operation at design frequency: 2.39
GHz
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MTM Power
#13
Pout 20 W
Frequency 2.44 GHz
Current 85 A
Voltage 505 kV
RF Pulse Length 1200 ns
Magnetic Field 1500 G
Low power operation in symmetric
mode
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Frequency Tuning-B Field
Frequency tuning of high power
shots consistent with anomalous
Doppler synchronism
High magnetic field-Cherenkov
synchronism-no frequency tuning Only low power (<100 W) observed
#14
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Starting Voltage
Starting voltage/current depends on
magnetic field
Frequency variation consistent
with eigenmode/PIC simulations
#15
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Conclusions
#16
First demonstration of coherent microwaves from electron beam/metamaterial 5 MW generated in antisymmetric mode at 2.4 GHz
Agreement between experiment, HFSS eigenmode and CST Particle Studio at low B
field
Lack of agreement between theory/simulation for high B field/symmetric mode
excitation
MTMs may have applications for future amplifier/microwave component designs
Potential future work: develop more accurate theory of beam-wave interaction,
more accurate PIC simulations to describe power in both modes
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Acknowledgements
MURI collaborators LSU
UNM
Ohio State
UC-Irvine
SLAC
Haimson Research
Corporation
MIT WAB-students Samantha Lewis
Xueying Lu
Alexander Soane
Sam Schaub
Haoran Xu
JieXi Zhang
This research was supported by AFOSR MURI Grant FA9550-12-1-0489
administered through the University of New Mexico.
MIT WAB–staff Rick Temkin
Ivan Mastovsky
Michael Shapiro
William Guss
Paul Woskov
Sudheer Jawla
Emilio Nanni
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