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
Motivation
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
Dispersion Diagram - TE01 Gyro-TWT
w = sW + k v
c
10
100 kV, v^/vz=1.0
z z
TE
02
6
TE
s=2
01
w
wr /c
8
TE
4
21
0
TE
s=1
2
-3
11
-2
-1
0
1
2
3
k r
z w
Must Suppress TE11(1) , TE21(1) and TE02(2) Gyro-BWO Interactions
Stable Beam Current (Absolute Instability at Cutoff)
Beam Current can be Higher for Lower v^/vz and Lower Bo/Bg
1000
B /B = 1.00
o
0.98
100
0.96
10
s
I (A)
100 kV,
v^/vz=1.0
g
1
Design Values
0.1
0
0.5
1
1.5
2
2.5
v /v
^
z
Unloaded TE01(1) Circuit is Stable for 5 A, v^/vz=1.0, and Bo/Bg=1.0
Gyro-BWO Stability in Lossy TE01(1) Circuit
100 kV, 5 A, v /v = 1.0
• Wall is Coated with Lossy Graphite
to Suppress Gyro-BWO
•
(2)
TE
TE
z
(1)
21
02
L /r
c w
60
[ NTHU's Technique,
PRL 81, 4760 (1998)]
^
80
r/rcopper = 7.104 yields Stability and
100 dB Loss for 14.5 cm Circuit
40
TE
11
20
0
2
10
(1)
10
3
10
r/r
4
copper
10
5
10
6
Power Growth in Lossy Single-Stage Device
Self-Consistent Large-Signal Simulation Code
• Large-Signal Gain = 50 dB
• Efficiency = 28%
• Peak Power = 140 kW
CW Wall Loading < 50 W/cm2
92.25 GHz
lossy wall
6
100 kV, 5 A, v^/vz =1
Dvz/vz = 5%
10
r/rCu = 70,000
5
10
4
• Final 2.5 cm is unloaded to avoid
damping high power wave
Power (W)
10
• Electron efficiency is nearly
independent of loss
Cu wall
loss taper
P = 5.0 W
in
1.25 W
3
10
0.3 W
2
10
1
10
0
10
-1
10
-2
10
0
5
10
z (cm)
15
Predicted Saturated Bandwidth
5% Bandwidth is Predicted
•
Dw/w = 5%
200
• rw = 2.01 mm
• rc/rw = 0.45
•
r/rcopper = 70,000
30
100
20
50
10
out
• Gain = 50 dB
150
(kW)
h = 28%
P
•
• Llossy = 11.0 cm
• Lcopper = 2.5 cm
• Lloss-taper = 1.0 cm
• Lcircuit = 14.5 cm
7
0
90
92
94
96
98
Frequency (GHz)
0
100
Efficiency (%)
Dv /v = 0%
z z
5%
• Pout = 140 kW
40
Gyro-TWT Circuit has been Fabricated
MIG Connection
Input Coupler Interaction Region
Output Coupler Collector
30 cm ruler
Axial View
Gyro-TWT Circuit has been Fabricated
Cross-Section of Coaxial Coupler
Rectangular Input Waveguide
Coaxial Cavity
Interaction Circuit
0 dB TE01 Input Coupler
Azimuthal Phase-Velocity Coupler
• HFSS Design
• Similar to
– UCLA’s TE81
Gyro-TWT Coupler
– NRL’s Gyroklystron
Coax Coupler
• All Modes are Matched
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 Analyzer
12
Set-up for
Coupler Measurement
Bandwidth of Coaxial Input Coupler
• Coupler exhibits > 2 dB coupling for 3% bandwidth
• Performance is limited by cutoff of short
Cutoff of short
Predicted for 93.0 - 96.5 GHz
> 1 dB
•Selectivity
> 40 dB
•Return Loss (TE01) > 7 dB
•Return Loss (TE21) > 14 dB
•Return Loss (TE11) > 28 dB
-5
Coupling (dB)
•Coupling
0
-10
Coupling (HFSS)
-15
Coupling (Measurement)
-20
Return Loss (HFSS)
Feature: No tapering is needed
between coupler and gain region
-25
90
92
94
96
Frequency (GHz)
98
100
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.
These three modifications of the original display a 7% bandwidth.
0
original
Coupling (dB)
-3
optimization 1
-6
-9
optimization 2
-12
optimization 3
-15
90
15
92
94
96
98
100
102 f (GHz)
Measured Loss in Circuit
Interaction Circuit has been Coated with Aquadag
Aquadag is a Carbon Colloid with r/rCu=70,000 and dskin=0.06 mm
Insertion Loss (dB / 12 cm)
Measurements versus HFSS Modeling
HFSS-Copper Guide
0
HFSS-Resistive Guide
( r/r =70,000)
90 dB Loss Measured
at 93 GHz
Cu
-50
-100
HFSS-Copper Guide with Inner
Semiconductor Tube
( Dr=0.05 mm, r/r =70,000)
-150
Cu
r =2.01 mm
w
-200
90
92
94
96
98
Frequency (GHz)
100
Single-Anode MIG (100 kV, 5 A, v^/vz = 1
• Designed with FINELGUN
• Fabricated by NTHU
• Mo Coating - Edge Emission
•
•
•
•
•
•
•
•
•
•
Cathode Angle
Magnetic Compression
Guiding Center Radius
Cathode Radius
Emitting Strip Length
Guiding Center Spread
Axial Velocity Spread
Electric Field
Cathode Loading
Jemis/JL
74o
32
0.9 mm
5.1 mm
1.9 mm
10%
5%
70 kV
9 A/cm2
0.3
MIG Has Been Activated
Cathode Stalk
Very Steep Cathode (74)
Emitting Ring
I-V Characteristic of MIG
25
780degree
820degree
20
845degree
1010degree
15
dc
I (mA)
898degree
10
5
0
0
100 200 300 400 500 600 700 800
V (V)
dc
Superconducting Magnet Profile
• 50 kG ± 0.1% over 50 cm
• Large 6" ID Bore
• Refrigerated
Field Profile of the
Four Independent Coils
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 Dw/w=5% and h=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 Dvz/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