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140kW, 94GHz Heavily Loaded TE 01 Gyro-TWT. D.B. McDermott, H.H. Song, Y. Hirata, A.T. Lin 1 , T.H. Chang 2 , K.R. Chu 2 and N.C. Luhmann, Jr. Department of Applied Science, UC Davis 1 Department of Physics, UCLA 2 Department of Physics, NTHU - PowerPoint PPT Presentation
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140kW, 94GHz Heavily Loaded TE01 Gyro-TWT
D.B. McDermott, H.H. Song, Y. Hirata, A.T. Lin1,
T.H. Chang2, K.R. Chu2 and N.C. Luhmann, Jr.
Department of Applied Science, UC Davis 1 Department of Physics, UCLA 2 Department of Physics, NTHU
This work has been supported by AFOSR under Grants
F49620-99-1-0297 (MURI-MVE) and F49620-00-1-0339.
Outline
• Small-Signal Design for Stability
– Wall Loss
• Large-Signal Characteristics
• Circuit Components
Why Gyro-TWT?
• Wider Bandwidth than Gyro-Klystron
• Higher Circuit Efficiency Higher Power Capability
Why TE01 Mode?
• Low Loss
• Well Centered for MIG Electron Beam (Peaks for r/rw=0.5)
• Azimuthal Symmetry is Favorable for MIG Beam
• Field Pattern is Unique (Jz=0 and Er=0)
- Useful for Mode Selective Circuit
Motivation
Dispersion Diagram - TE01 Gyro-TWT
100 kV, v/vz=1.0
Must Suppress TE11(1) , TE21
(1) and TE02(2) Gyro-BWO Interactions
0
2
4
6
8
10
-3 -2 -1 0 1 2 3
kzrw
TE02
TE21
TE11
TE01
w = sWc + k
zv
zw
r w/c
s = 1
s = 2
Stable Beam Current (Absolute Instability at Cutoff)
Beam Current can be Higher for Lower v/vz and Lower Bo/Bg
100 kV, v/vz=1.0
Unloaded TE01(1) Circuit is Stable for 5 A, v/vz=1.0, and Bo/Bg=1.0
0.1
1
10
100
1000
0 0.5 1 1.5 2 2.5
I s(A)
v/v
z
Bo/B
g = 1.00
0.98
0.96
Design Values
Gyro-BWO Stability in Lossy TE01(1) Circuit
• Wall is Coated with Lossy Graphite to Suppress Gyro-BWO
[ NTHU's Technique,
PRL 81, 4760 (1998)]
• copper = 7.104 yields Stability and 100 dB Loss for 14.5 cm Circuit 0
20
40
60
80
102 103 104 105 106L
c/rw
copper
TE02
(2) TE21
(1)
TE11
(1)
100 kV, 5 A, v/v
z = 1.0
Power Growth in Lossy Single-Stage Device
Self-Consistent Large-Signal Simulation Code
• Large-Signal Gain = 50 dB
• Efficiency = 28%
• Peak Power = 140 kW
100 kV, 5 A, v/vz =1
vz/vz = 5%
• Electron efficiency is nearly independent of loss
• Final 2.5 cm is unloaded to avoid damping high power wave
92.25 GHz
10-2
10-1
100
101
102
103
104
105
106
0 5 10 15
Pow
er (
W)
z (cm)
lossy wall Cu wall
loss taperCu
= 70,000
Pin = 5.0 W
1.25 W
0.3 W
CW Wall Loading < 50 W/cm2
Predicted Saturated Bandwidth
• ww = 5%
• Pout = 140 kW
• = 28%
• Gain = 50 dB
• rw = 2.01 mm
• rc/rw = 0.45
• copper = 70,000
• Llossy = 11.0 cm
• Lcopper = 2.5 cm
• Lloss-taper = 1.0 cm
• Lcircuit = 14.5 cm
5% Bandwidth is Predicted
7
0
50
100
150
200
0
10
20
30
40
90 92 94 96 98 100
Pou
t (kW
)
Efficiency (%
)
Frequency (GHz)
vz/v
z = 0%
5%
Gyro-TWT Circuit has been Fabricated
Axial View
MIG Connection Input Coupler Interaction Region Output Coupler Collector
30 cm ruler
Cross-Section of Coaxial Coupler
Gyro-TWT Circuit has been Fabricated
Rectangular Input Waveguide
Coaxial Cavity
Interaction Circuit
0 dB TE01 Input Coupler
• HFSS Design
• Similar to
– UCLA’s TE81 Gyro-TWT Coupler
– NRL’s Gyroklystron Coax Coupler
• All Modes are Matched
Azimuthal Phase-Velocity Coupler
TE51/TE01 Coax-Cavity Input Coupler
TE10 Rectangular Waveguide into TE51 Coax-Cavity
into TE01 Circular Waveguide
RF Measurement Set-up for Coupler and Circuit Loss
• MPI Flower-Petal TE10 / TE01
Transducers Give <1.3 VSWR over 5% Bandwidth
• DURIP W-Band Vector Network Analyzer at SLAC will Measure Optimized Components
W-Band Scalar Network AnalyzerSet-up for
Coupler Measurement
12
Bandwidth of Coaxial Input Coupler
Predicted for 93.0 - 96.5 GHz
•Coupling > 1 dB
•Selectivity > 40 dB
•Return Loss (TE01) > 7 dB
•Return Loss (TE21) > 14 dB
•Return Loss (TE11) > 28 dB
Feature: No tapering is needed between coupler and gain region
Cutoff of short
-25
-20
-15
-10
-5
0
90 92 94 96 98 100
Cou
plin
g (d
B)
Frequency (GHz)
Return Loss (HFSS)
Coupling (HFSS)
Coupling (Measurement)
• Coupler exhibits > 2 dB coupling for 3% bandwidth
• Performance is limited by cutoff of short
Future Coaxial Input Coupler
Although the initial Gyro-TWT experiment will employ the previous coaxial couplers,
plans have been initiated to develop an improved coupler for future experiments.
9 0 9 2 9 4 9 6 9 8 1 0 0 1 0 2
- 1 5
- 1 2
- 9
- 6
- 3
0
Cou
plin
g (d
B)
f (G H z )
o r ig ina l
o ptim iz a tio n 1
o ptim iz a tio n 2
o ptim iz a tio n 3
These three modifications of the original display a 7% bandwidth.
15
Measured Loss in Circuit
-200
-150
-100
-50
0
90 92 94 96 98 100Inse
rtio
n L
oss
(dB
/ 12
cm
)
Frequency (GHz)
HFSS-Copper Guide
HFSS-Copper Guide with Inner Semiconductor Tube (r=0.05 mm,
Cu=70,000)
HFSS-Resistive Guide (
Cu=70,000)
rw
=2.01 mm
Interaction Circuit has been Coated with AquadagAquadag is a Carbon Colloid with Cu=70,000 and skin=0.06 mm
Measurements versus HFSS Modeling
90 dB Loss Measured at 93 GHz
• Designed with FINELGUN• Fabricated by NTHU• Mo Coating - Edge Emission
• Cathode Angle 74o
• Magnetic Compression 32
• Guiding Center Radius 0.9 mm
• Cathode Radius 5.1 mm
• Emitting Strip Length 1.9 mm
• Guiding Center Spread 10%
• Axial Velocity Spread 5%
• Electric Field 70 kV
• Cathode Loading 9 A/cm2
• Jemis/JL 0.3
Single-Anode MIG (100 kV, 5 A, v/vz = 1
MIG Has Been Activated
Emitting Ring
Cathode Stalk
Very Steep Cathode (74)
I-V Characteristic of MIG
0
5
10
15
20
25
0 100 200 300 400 500 600 700 800
780degree
820degree
845degree
898degree
1010degree
I dc(m
A)
Vdc
(V)
Superconducting Magnet Profile
0
20
40
60
-50 0 50 100 150 200
z (cm)
Interaction
Gun
Field Profile of the Four Independent Coils
• 50 kG ± 0.1% over 50 cm
• Large 6" ID Bore
• Refrigerated
100W 94GHz TWT Input Driver
Hughes 987 Coupled-Cavity TWT
CPI 1kW EIO is Also Available
Summary
• UCD 94GHz Gyro-TWT has been Constructed - Capable of 140kW with ww=5% and =28%
• Circuit is Heavily Loaded to Suppress Gyro-BWO - Final 2.5 cm is Unloaded to Avoid Damping Saturated Wave
- Loss has Negligible Effect on Efficiency
- 90 dB Loss Measured at 93 GHz
• MIG was Designed with vz/vz = 5% and v/vz = 1.0- MIG has been Activated
• Coax Couplers were Designed with HFSS- Good Match for All Modes
- Very Short Length (5 mm)
- Input and Output Couplers have been Measured