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TE 21 Second-Harmonic Gyro-TWT Amplifier with an Axis-Encircling Beam S.B. Harriet* , D.B. McDermott, and N.C. Luhman PowerPoint Presentation
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TE 21 Second-Harmonic Gyro-TWT Amplifier with an Axis-Encircling Beam S.B. Harriet* , D.B. McDermott, and N.C. Luhman

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TE 21 Second-Harmonic Gyro-TWT Amplifier with an Axis-Encircling Beam S.B. Harriet* , D.B. McDermott, and N.C. Luhman - PowerPoint PPT Presentation


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TE 21 Second-Harmonic Gyro-TWT Amplifier with an Axis-Encircling Beam S.B. Harriet* , D.B. McDermott, and N.C. Luhmann, Jr. Department of Applied Science, University of California, Davis *Also with NSWC Crane This work has been supported by AFOSR under Grant F49620-99-1-0297 (MURI MVE).

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slide1

TE21 Second-Harmonic

Gyro-TWT Amplifier with an

Axis-Encircling Beam

S.B. Harriet*, D.B. McDermott, and N.C. Luhmann, Jr.

Department of Applied Science, University of California, Davis

*Also with NSWC Crane

This work has been supported by AFOSR under Grant F49620-99-1-0297 (MURI MVE).

Distribution Statement A: Approved for Public Release; Distribution is Unlimited

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slide2

Overview

  • Applications include mm-Wave Radar and Broadband Communications
  • Harmonic Operation Provides Higher Power and Greater Stability
  • Significant Reduction of Magnetic Field from Harmonic Operation
  • Axis-Encircling Electrons Provide Strongest Harmonic Interaction
  • Second-Harmonic TE21 Gyro-TWT Designed for
    • 50 kW at 30 GHz with 20% Efficiency
    • 30 dB Saturated Gain
    • 3% Saturated Bandwidth
  • Axis-Encircling Electron Beam Produced by Northrop Grumman Cusp Gun

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previous ucd 200 kw te 21 2 gyro twt with mig
Previous UCD 200 kW TE21(2) Gyro-TWT With MIG

MIG TE21(2) Gyro-TWT

Produced 200 kW of output power

Efficiency reduced because electrons were constrained to a fixed azimuth so some electrons experienced a weak RF field while others oversaturated in a strong RF field.

Cusp-Gun TE21(2) Gyro-TWT

Axis-encircling beam will yield full (20%) efficiency because electrons rotate through the peaks and nulls.

Efficiency will nearly double and gain will increase

Cusp

MIG

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Measured Bandwidth of

200 kW MIG TE21(2) Gyro-TWT

slide4

Higher Power at Higher Harmonics

Threshold Beam Current for Absolute Instability

70 kV, rgc= 0

Oscillation at Cutoff of Operating Mode Limits Gyro-TWTs

Start-Oscillation Current is Higher

for Harmonic Operation

Higher Current Yields Higher Power

Is = 5 A Gives 30% Safety Margin

for Planned 3.5 A Beam

Is (A)

v / v||

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slide5

Mode-Selective Interaction Circuit

Previous Experiment Measured Insertion Loss

TE21 Operating Mode < 1.5 dB

TE11 Unwanted Mode > 24 dB

Slices

Suppress Odd-Order Azimuthal Modes by Interrupting their Wall Currents

Circular Waveguide with Two Orthogonal Slices through the Axis

Lossy MgO-SiC

Vacuum Jacket

Circular Waveguide

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circuit dispersion diagram
Circuit Dispersion Diagram

Competing Modes must be Suppressed

Second Cyclotron Harmonic Line Grazes the TE21 Mode

s=4

TE01

TE31

TE41

Odd-Order Azimuthal Modes Suppressed by Sliced Circuit

s=3

s=2

TE41(4) is Strongest

Gyro-BWO Threat

rw / c

TE21

TE11

s=1

Oscillation can Occur at Cutoff

(Absolute Instability)

 = sc + kzvz

No Interaction at First Cyclotron Harmonic

kzrw

For Axis-Encircling Beam only s=m Modes are Excited

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gyro bwo oscillation
Gyro-BWO Oscillation

Suppress Gyro-BWO Instability with Distributed Loss

  • TE41(4) is Strongest Competing Mode in Mode Selective Circuit
  • Loss Added to Circuit Wall to Suppress TE41(4) Gyro-BWO
  • Figure shows Dependence on Wall Resistivity of Critical Length for TE41(4) Gyro-BWO

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slide8

Spatial Power Growth

Loss added to first 30.5 cm of circuit to suppress Gyro-BWO

Last 11.5 cm of circuit

not loaded to avoid attenuating the high power wave

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constant drive bandwidth
Constant Drive Bandwidth

Predicted Bandwidth is Greater than 3%

Device Parameters

Voltage 70 KV

Current 3.5 A

 = v /v|| 1.2

vz / vz 7%

Magnetic Field, Bo 5.48 kG

B/Bg 0.99

Cutoff Frequency 28.6 GHz

Guiding Center Radius 0.0 rw

Circuit Radius, rw 0.509 cm

Lossy Circuit Length 30.5 cm

Wall Resistivity 2300 x copper

Total Circuit Length 42.0 cm

Saturated Drive Bandwidth

(Dvz/vz=0%, 7%, 10%)

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slide10

Magnetic Circuit

Water Cooled Copper Coil

Interaction Circuit Region

Pole Piece

NG Cusp Gun Magnetics

Cathode

Vacuum Jacket of Gyro-TWT

  • - Magnetic Circuit Configuration:
    • Incorporates gun coil and pole pieces provided by Northrop Grumman
    • Water cooled copper magnet coils and steel pole pieces for interaction region
    • Good match to Northrop Grumman recommended magnetic fields in field reversal region

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slide11

Magnetic Field Profile

Magnetic Field Profile Designed and Simulated in Maxwell 2D®

  • Provides field reversal and fast rise required by Cusp gun
  • Provides flat region for interaction circuit
  • Designed for stability from gyrotron oscillations in each section of the device.

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northrop grumman cusp electron gun
Northrop Grumman Cusp Electron Gun

UCD TE21(2) Gyro-TWT Cusp Gun developed by Northrop Grumman

  • NG Cusp Gun Produces Axis-Encircling Electron Beam
  • Axial Electron Beam Starts Spinning Due to vz x Br Force

in Magnetic Reversal Region

EGUN Simulation of Cusp Gun with new Magnetics

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0 db input coupler for te 21 2 gyro twt
0 dB Input Coupler for TE21(2) Gyro-TWT
  • Multi-Hole Directional Coupler was Designed with HFSS
  • All Modes are Matched due to Upstream Termination
  • Excellent Selectivity to TE21 Mode
  • -1 dB Coupling in Previous Gyro-TWT Experiment

Schematic

Excited TE21 Wave

Input TE10 Mode

Input Waveguide

Interaction Waveguide

Excited TE21 Mode

HFSS Intensity Plot of the

Input and Generated Waves

13 of 17

hfss simulation of 0 db input coupler
HFSS Simulation of 0 dB Input Coupler

< 0.5 dB Coupling Loss Simulated over the 28.5 – 31.5 GHz Bandwidth

of the Gyro-TWT Amplifier

> 45 dB Round Trip Return Loss for the Operating TE21 Circular Mode

from 28.5 – 31.5 GHz

14 of 17

0 db input coupler for te 21 2 gyro twt15
0 dB Input Coupler for TE21(2) Gyro-TWT

Three dimensional view of coupler being fabricated for the gyro-TWT

15 of 17

slide16

RF Driver for Gyro-TWT

CPI Ka-Band TWT Driver

ETM Modulator Supply for Driver TWT,

16 of 17

summary
Summary
  • A novel TE21 Second-Harmonic Gyro-TWT Amplifier with an axis-encircling beam from a Northrop Grumman Cusp Gun is being constructed at UC Davis to demonstrate the advantages of a large orbit axis-encircling beam in a harmonic Gyro-TWT.

Cusp-Gun Second-Harmonic Gyro-TWT Amplifier

Frequency 30 GHz

Output Power 50 kW

Efficiency 20 %

Bandwidth 3 %

Gain 30 dB

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