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

Outline

Introduction

Metamaterial design and simulations

Experimental results

Conclusion

#2

#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

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

Outline

Introduction

Metamaterial design and simulations

Experimental results

Conclusion

#5

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

Cherenkov vs Anomalous Doppler

Cherenkov 𝜔 = 𝑘𝑧𝑣𝑧 Does not tune with B field

Anomalous Doppler 𝜔 = 𝑘𝑧𝑣𝑧 − Ω𝑐/𝛾 Tunes with B field

#7

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

Cold Test

#9

Outline

Introduction

Metamaterial design and simulations

Experimental results

Conclusion

#10

HPM Metamaterial Experiment

Lens

Electron Beam

SolenoidVacuum

Chamber

Viewport

Collector

Electric

Standoff

RF Load

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Bethe Hole Coupler

MTM Structure

CSRRs

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

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

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

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Starting Voltage

Starting voltage/current depends on

magnetic field

Frequency variation consistent

with eigenmode/PIC simulations

#15

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

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