94 ghz heavily loaded te01...
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A high performance, high power TE01 gyro-TWT has been constructed at UCD to be driven by a 100 kV, 5 A, v⊥/vz=1.0 MIG electron beam with ∆vz/vz=5%.
The single-stage amplifier is loaded with 90 dB of loss for stability and is predicted by our large-signal simulation code to generate 140 kW at 94 GHz with 28% efficiency, 50 dB saturated gain and 5% bandwidth.
Linear theory has been used to determine the threshold start-oscillation beam current for absolute instability and the critical lengths for the potential harmonic gyro-BWO interactions.
This work has been supported by AFOSR under Grants F49620-95-1-0253 (MURI-HPM) and F49620-99-1-0297 (MURI-MVE).
94 GHz 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, Hsinchu, Taiwan
1a
94 GHz Heavily Loaded TE01 Gyro-TWT Amplifier
Objectives
Approach Accomplishments
50 kG Superconducting Magnet
• Extend mature TWT technologyinto the millimeter range
• Develop stable W-band 100kWgyro-TWT amplifier
• Gyro-TWT’s offer wide bandwidth
• TE01 mode transmits high power
• Loss stabilizes amplifier
• High power W-Band gyro-TWT has been constructed
- MIG gun has been built - Stability codes determined needed loss- Circuit has been fabricated- Couplers and loss have been measured- Large-signal code predicts η = 28%
1b
Why Gyro-TWT?
• Wider Bandwidth than Gyro-Klystron
• Higher Circuit Efficiency ª 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
1c
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
kzr
w
TE02
TE21
TE11
TE01
ω = sΩc + k
zv
zω
r w/c
s = 1
s = 2
2a
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
2b
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)]
• ρ/ρcopper = 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
ρ/ρcopper
TE02
(2) TE21
(1)
TE11
(1)
100 kV, 5 A, v⊥/v
z = 1.0
2c
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 taperρ/ρCu
= 70,000
Pin
= 5.0 W1.25 W
0.3 W
CW Wall Loading < 50 W/cm2
3a
Predicted Saturated Bandwidth
• ∆ω/ω = 5%• Pout = 140 kW
• η = 28%• Gain = 50 dB• rw = 2.01 mm
• rc/rw = 0.45
• ρ/ρcopper = 70,000• Llossy = 11.0 cm• Lcopper = 2.5 cm
• Lloss-taper = 1.0 cm• Lcircuit = 14.5 cm
5% Bandwidth is Predicted
0
50
100
150
200
0
10
20
30
40
90 92 94 96 98 100
P out (k
W)
Efficiency (%
)
Frequency (GHz)
∆vz/v
z = 0%
5%
3b
Gyro-TWT Circuit has been Fabricated
Axial View
MIG Connection Input Coupler Interaction Region Output Coupler Collector
30 cm ruler
3c
Cross-Section of Coaxial Coupler
Gyro-TWT Circuit has been Fabricated
Rectangular Input Waveguide
Coaxial Cavity
Interaction Circuit
4a
0 dB TE01 Input Coupler
• HFSS Design
• Similar to
– UCLA’s TE81Gyro-TWT Coupler
– NRL’s GyroklystronCoax Coupler
• All Modes are Matched
Azimuthal Phase-Velocity Coupler
4b
TE51/TE01 Coax-Cavity Input Coupler
TE10 Rectangular Waveguide into TE51 Coax-Cavity
into TE01 Circular Waveguide
4c
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
5a
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
5b
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.
90 92 94 96 98 100 102-15
-12
-9
-6
-3
0
Cou
plin
g (d
B)
f (GHz)
original
optimization 1
optimization 2
optimization 3
These three modifications of the original display a 7% bandwidth.
5c
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, ρ/ρ
Cu=70,000)
HFSS-Resistive Guide (ρ/ρ
Cu=70,000)
rw
=2.01 mm
Interaction Circuit has been Coated with AquadagAquadag is a Carbon Colloid with ρ/ρCu=70,000 and δskin=0.06 mm
Measurements versus HFSS Modeling
90 dB Loss Measured at 93 GHz
6a
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
6b
100W 94GHz TWT Input Driver
Hughes 987 Coupled-Cavity TWT
CPI 1kW EIO is Also Available
6c
• 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
7a
MIG Has Been Activated
Emitting Ring
Cathode Stalk
Very Steep Cathode (74°)
7b
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)
7c
Summary
• UCD 94GHz Gyro-TWT has been Constructed- Capable of 140kW with ∆ω/ω=5% and η=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
8a
8b
For Further Information (TE01 Gyro-TWT)
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