Transcript 100 kW, 94 GHz TE01 Gyro-TWT

Second-Harmonic Fundamental Mode
Slotted Peniotron
L.J. Dressman*, D.B. McDermott, and N.C. Luhmann, Jr.
University of California, Davis
*Also NAVSEA, Crane
D.A. Gallagher
T.A. Spencer
Northrop Grumman Corp.
Air Force Research Lab.
Pulsed Power Plasma Science Conference, PPPS-2001
Las Vegas, Nevada
June 7-22, 2001
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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1a
Abstract
The harmonic peniotron has been demonstrated to be a highly efficient generator of
millimeter-wave power [1]. Since a practical peniotron design must provide immunity to
mode competition from gyrotron interactions as well as high device efficiency, the UC Davis
peniotron design [2] employs an overcoupled interaction cavity for a predicted device
efficiency of 47% at 34 GHz. Stability will be insured by operation in the lowest order mode
of a slotted four-vane (magnetron type) circuit, the p/2 mode. The TE11-like p/2 mode
couples well to the TE11 mode of the circular output waveguide through the 2.5 mm radius
iris at the end of the cavity. The output diffraction coupling configuration results in heavy
loading of higher order axial modes and avoids mode conversion in the output waveguide.
For diagnostic purposes, the experimental device will also incorporate side-wall coupling to
the cavity. The peniotron will operate with a 70 kV, 3.5 A, =1.5, axis-encircling electron
beam generated by a recently developed Northrop Grumman Cusp gun [3]. Large-signal
simulation of the interaction predicts an electronic efficiency of 58% and an extracted power
output of 120 kW (47% device efficiency). The overall efficiency can be raised to 57% by
use of a depressed collector.
[1] T. Ishihara, et al., IEEE Trans. on Electron Devices 46, 798 (1999).
[2] D. B. McDermott, et al., IEEE Trans. on Plasma Science 28, 953 (2000).
[3] D. Gallagher, et al., IEEE Trans. on Plasma Science 28, 695 (2000).
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Second-Harmonic Fundamental Mode Slotted Peniotron
Objectives
TE11-Like Mode in Slotted Cavity
• Improve device efficiency of Tohoku’s
recent third-harmonic h=35% peniotron
• Achieve device efficiency of 50%
in harmonic gyro-device
• Foundation for peniotron-amplifiers
Approach
Accomplishments
• Axis-encircling electrons generate • Received two Northrop Cusp guns
mth-order azimuthal mode
in sth-harmonic peniotron if m=s+1 • 34 GHz 2nd-harmonic peniotron desig
• Slotted circuit enhances interaction - 125 kW with 47% device efficiency
and allows stable, lowest-order mode - Employs Northrop Cusp gun
to have desired mth-order symmetry • 34 GHz slotted cavity and coupler wa
• Cusp gun produces needed
designed with HFSS for high efficienc
axis-encircling electron beam
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1c
Description of Peniotron
–
–
–
–
–
Fast-Wave Device
Similar to Gyrotron
Driven by Electrons’ Transverse Velocity
Optimized for Axis-Encircling Electron Beam
Resonance Condition with TEm1 Wave:
 = sc + kzvz
s  Cyclotron Harmonic
s = m for Gyrotron
s = m-1 for Peniotron
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(Synchronism)
(Asynchronism)
2a
Motivation for Peniotron
• Proven High Efficiency
– 75% Electronic Efficiency
• Predicted Higher Efficiency
– Efficiency >80% is Predicted
• Gyrotron Replacement
– Higher Efficiency than Gyrotron
– High Frequency Source well suited for
Cyclotron Harmonic Emission
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2b
State of the Art
• Tohoku University Team Recently Demonstrated
Extremely High Efficiency
– [ T. Ishihara, et al., IEEE-ED 46, p. 798, 1999 ]
– 30 GHz, 3rd-Harmonic Peniotron
– Slotted (Magnetron Type) Waveguide, 2p Mode
– Significant Achievement: Electronic Efficiency of 75%
– 35% Device Efficiency due to Critically Coupled Cavity
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Peniotron Interaction
• Peniotron Resonance
with TEm1 Wave:
 = (m-1)c + kzvz
• Electrons Move Forward
by 360o each Orbit
• Wave Appears as “DC”
Electric Field
• Electrons E x B Drift to
Deceleration Phase
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3a
UCD Peniotron Features
• Second-Harmonic Operation - 34 GHz
• Operation in p/2 Cavity Mode
–
–
–
–
–
4-Vane Slotted Waveguide
Lowest Order Mode
Contains Needed m=3 Component
Suppresses Gyrotron Modes
Easily Couples to Circular Output
Waveguide
Slotted Circuit
TE11-Like Mode
with TE31 Content
• New Northrop Grumman Cusp Gun
– High Quality Axis-Encircling Beam
– High Efficiency Interaction
– High Power (125 kW)
E-Field
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3b
Dispersion Diagram/Mode Selection
Strongest Competing Mode
is 4th-Harmonic Gyrotron
Lowest Order Mode
Ensures Stability
2p (m=0,4)
4-Vane Slotted Circuit Yields
m=3 for Lowest Order Mode
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p (m=2)
3
Mode Selection for
Axis-Encircling Electrons:
2
rw/c
s = Cyclotron Harmonic
m = s for Gyrotron
m = s+1 for Peniotron
p/2 (m=1,3)
1
Peniotron
0
-2
-1
0
1
2
kzrw
4a
Magnetic Tuning Curve
Gyrotron Starting Current
is Above Peniotron’s
Nearest Competing Mode:
4th-Harmonic Gyrotron
6
Operating
Current
5
Start oscillation current for
competing 4th-Harmonic
Gyrotron is four times higher
than Peniotron start current.
Is (A)
4
3
2
Peniotron
Gyrotron
1
0
5.5
6.0
6.5
B0 (kG)
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7.0
7.5
Excellent Stability Predicted
4b
Power and Efficiency
Peniotron has been Simulated with Nonlinear Code
Efficiency Predictions:
100
200
hdev
Device Efficiency with
Depressed Collector
57%
Collector Potential
12.8 kV
Pout
150
hdep
60
100
40
Pout (kW)
58%
47%
Efficiency (%)
80
Electron Efficiency
Device Efficiency
helec
50
20
0
0
0
1
2
3
4
5
Ib (A)
50% Efficiency Predicted
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Design Parameters
Beam Voltage
Beam Current
Velocity Ratio, v/vz
Magnetic Field
Velocity Spread, vz/vz
Guiding Center Spread, rc/rL
Mode
Axial Mode Number
Vane Depth, b/a
Electron-Vane Ratio, rL/a
Inner Vane Radius, a
Cavity Length
Slot Angle, o
Unloaded Q, Q0
Loaded Q, QL
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70 kV
3.5 A
1.5
6.5 kG
5%
10%
p/2
1
1.45
0.65
1.82 mm
31 mm
22.5
1900
357
2 
a
rL
b
5a
Cavity Design
Diagnostic Coupling
Ports
Output Circular
Waveguide r=4.5 mm
Slotted
Cavity
Circular Iris
(Removable)
Q0=190
0
Cutoff Drift Tube
Iris Radius for Critical Coupling:
2.35mm, QL=990
Iris Radius for Over Coupling:
2.55mm, QL=357
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5b
Cavity Design–Diffraction Coupling
Couples to TE11 Circular
Waveguide Mode
1st Axial Mode,
34 GHz
0
S11 (dB)
-1
-2
3rd Axial Mode, QL=59
-3
2nd Axial Mode, QL=102
-4
Operating Mode, QL=357
-5
33
Diffraction Coupling
34
35
36
37
38
39
40
Frequency (GHz)
– Overcoupled for High Device Efficiency - 47% Predicted
– Efficiency Increased by Depressed Collector - 57% Expected
– Suppresses Higher Order Axial Modes
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Diagnostic Sidewall Couplers
Couples to
TE10 Mode
Diagnostic Coupling
-30
E
E
Coupling to Operating Mode
Coupling to 2nd Axial Mode
E
S21 (dB)
-40
-50
-60
33
Diagnostic Coupling
34
35
36
37
38
39
40
Frequency (GHz)
– Couples to standard WR-28 rectangular waveguide
– Coupling to adjacent slots will load both components of
circularly polarized wave
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6a
Output Mode Conversion
Mode Conversion Occurs Only at Higher Frequencies
- TM11 Mode is Excited
0.5
0.4
TM11 Output
S21
0.3
0.2
TE11 Output
0.1
0.0
34
36
38
40
42
44
Frequency (GHz)
Conversion to TM11 Mode
Only Above 40.0 GHz
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Cusp Gun
UCD Peniotron will use state-of-the-art Cusp gun
developed by Northrop Grumman
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7a
Cusp Gun
Axis Encircling Beam Parameters:
Beam Voltage
Beam Current
Velocity Ratio, v/vz
Velocity Spread, vz/vz
Guiding Center Spread, rc/rL
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70 kV
3.5 A
1.5
5%
10%
7b
Superconducting Magnet
Four Independently
Controlled Coils
Cusp Gradient from
Internal Gun Coil and
Two Supplemental Gun
Coils
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Gun Coil
Components
7c
Summary
• Peniotron Demonstrated Very High Efficiency
(Tohoku)
• UCD Peniotron Designed For High Device Efficiency
• p/2 Slotted Circuit Mode Provides Stability and
m=3 Component for s=2 Peniotron
• Overcoupled Cavity Provides High Device Efficiency
• Northrop Grumman Cusp Gun Provides Required
Axis-Encircling Beam
50% Device Efficiency Predicted
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8a
Future Work
• Circuit Fabrication
• Cold Test
• Electron Beam Test
• Hot Test the Peniotron
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Sign Up Sheet
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8c