Post on 16-Jul-2020
Prospects for an Inductive Output Tube
(IOT) Based Source
Brian Beaudoin February, 10 2016
Institute for Research in Electronics & Applied Physics 1
https://en.wikipedia.org/wiki/High_Frequency_Active_Auroral_Research_Program.
Outline
• Introduction and Team • Why Inductive Output Tubes (IOTs) and what are the
technical challenges • Multi-Staged approach
– We are designing a high peak power IOT based source based on a Magnetron Injection Gun (MIG) with a Mod-Anode
– Using a gridded gun for prototyping, in order to optimize various subsystems:
• Grid/Mod-Anode modulator • Frequency tunable constant impedance cavity and electronic feedback
control
• Conceptual system design for a barge with a MIG-IOT • Summary and plans
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Graduate and Undergraduate Student Team
Amith Narayan Connor Thompson
Quinn Kelly
Charles Turner
Jayakrishnan Karakkad Nikhil Goyal
3
Various RF Sources • Triodes can reach high peak power but the control grid
limits the average power (pulse length). Anode dissipation and breakdown is still a limiting problem, requiring a large cathode area to cope with breakdown limits. – Thales 116, 2.2 MW up to a 700 ms pulse width operating at
200 MHz – 7835, 4MW up to a 2000 ms pulse width operating at 250 MHz
4 - H. Haseroth, CERN, Internal, 2002. - Trevor A. Butler, FNAL-LINAC Modulator, Internal 2014.
CERN LHC FNAL LINAC
- G. Clerc, JP Ichac, C. Robert, A New Generation of Gridded Tubes for Higher Power and Higher Frequencies, 17th Particle Accelerator Conference, Vancouver, Canada, 1997.
Various RF Sources • Tetrodes and Diacrodes do not have the problem of
excessive control grid current as a result of the screen. Anode dissipation and breakdown is still a limiting problem, requiring a large cathode area to cope with breakdown limits. Diacrodes circumvent the non-uniformity in power along the screen-grid, by implementing a double ended triode configuration. – Thales 526, 1.6 MW up to a 2.2 ms pulse width operating at 200
MHz or 300 kW CW – Thales 781, 300 kW CW operating at 110 MHz – Thales 628, 3 MW up to a 2.5 ms pulse width operating at 200
MHz or 1 MW CW
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- G. Clerc, JP Ichac, C. Robert, A New Generation of Gridded Tubes for Higher Power and Higher Frequencies, 17th Particle Accelerator Conference, Vancouver, Canada, 1997.
Various RF Sources • IOTs do not have the problem of anode dissipation and
breakdown. Control grid limits the average power (pulse length). Unlike Klystrons, they don’t require long lengths for velocity modulations. – E2V (IOTD2130), 135 kW CW operating between 470 – 810
MHz – CPI (VKP-9050), 90 kW CW operating at 500 MHz
6 - http://www.e2v.com/products/rf-power/inductive-output-tubes/ - https://en.wikipedia.org/wiki/Inductive_output_tube
University of Maryland's MIG-IOT Source • A Magnetron Injection Gun (MIG) based IOT allows for
a thin annular beam with minimal energy spread to be modulated with a mod-anode. This reduces the complexity that results from intercepted current and heat loading when utilizing a grid to modulate the beam.
• Pulse mode (“Class-D”) operation, simplifies driver circuitry as well as enhances efficiency.
• Technical Challenges: – IOTs are currently not available in the 1-10 MHz frequency range. – Cavity tuning at MHz Frequencies with mechanical frequency sweeping.
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An Initial Design Based on an Existing Emitter from HeatWave Labs
Annular Beam Cathode (Emitter) No intercepted current (grid-less) Beam is controlled through a mod-anode
Beam guided by Solenoid
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Emitter
Focus
Focus
Defocusing occurring at high currents
Gap
Gap
Mod-Anode
- Jayakrishnan A. Karakkad, Brian L. Beaudoin, John C. Rodgers, Gregory S. Nusinovich, Thomas M. Antonsen Jr., IVEC 2016.
Michelle Simulations
Beam 70 kV at 15 A = 1 MW
Current density ?
Modified Emitter Design to Increase Electrostatic Focusing in the Emitter Region
Annular Beam Cathode (Emitter)
Beam guided by Solenoid
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Emitter
Focus
Focus
Decreased defocusing occurring at high currents Gap
Gap
Mod-Anode
- Jayakrishnan A. Karakkad, Brian L. Beaudoin, John C. Rodgers, Gregory S. Nusinovich, Thomas M. Antonsen Jr., IVEC 2016.
No intercepted current (grid-less) Beam is controlled through a mod-anode
Beam 70 kV at 15 A = 1 MW
- Jayakrishnan A. Karakkad, Brian L. Beaudoin, John C. Rodgers, Gregory S. Nusinovich, Thomas M. Antonsen Jr., IVEC 2016.
Mod
-Ano
de V
olta
ge (V
) B
eam
Cur
rent
(A)
Mod-Anode Voltage vs. Time
Square wave input pulse driving mod-anode
Pulse mode (“Class-D”) operation
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Mod-Anode swings from cutoff 70.185 kV to saturation 67.85 kV
Time-Domain Simulation of the MIG
Beam Current vs. Time
15 A
0 A
-67.85 kV
-70.185 kV
60 ns
Emitted current of 15 A at a 60 ns pulse width
- Gregory S. Nusinovich, Connor Thompson, Brian L. Beaudoin, Jayakrishnan A. Karakkad, Thomas M. Antonsen Jr., IVEC 2016.
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Limitations of Beam Deceleration across a Gap Resonant circuit
Rb/Rw = 0.9 Fixed z/L = 1
L = Rw Maximum voltage also decreases as the ratio of beam radius (Rb) to pipe radius (Rw) decreases.
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Phase-Space vs Position at Different Voltages
Deceleration of 60.7 kV
- Gregory S. Nusinovich, Connor Thompson, Brian L. Beaudoin, Jayakrishnan A. Karakkad, Thomas M. Antonsen Jr., IVEC 2016.
Rb/Rw = 0.81 L/Rw = 3.45
Deceleration of 60.5 kV
Deceleration of 56 kV
Gap
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Simulated Phase-Space vs Position at Different Voltages
- Gregory S. Nusinovich, Connor Thompson, Brian L. Beaudoin, Jayakrishnan A. Karakkad, Thomas M. Antonsen Jr., IVEC 2016.
5.2166.9456
0.92
keVkeV
η
η
= −
=
Theoretical Efficiency
Conceptual Drawings of the UMD-MIG
0.36 m
Lawrence Ives of Calabazas Creek Research, Inc. Proposed cost ~ $245k / tube with a spare emitter Proposed timeframe ~ 9 months
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Beam
Emitter 0.33 m
Ion Pumps
Prototyping Studies for Subsystem Optimization using a Gridded Gun
from HeatWave Labs
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Progress on HeatWave Labs Prototyping Gridded Gun
Simulation of Solenoid Field
Simulation Radius vs. Axial Position Beam Specifications Cathode voltage: 20 kV Beam current: 3.3-5A Grid drive: +235 v Perveance: 2µPervs Macro Pulse width: 100µs max Duty cycle: 0.04 max (or 400Hz) Grid power dissipation: 3 W max
Axial Position (mm)
R B
eam
Pro
file
(mm
)
50 100
1
2
3
4
5
6
7
inter 0.06b
II =
Emitter
Intercepted current
0
Gun being manufacturing by HeatWave Labs.
Prototyping Test Stand Vacuum Chamber
Controls and Scopes
Heater and Power Supplies Diagnostics include:
1 – Pressure gauge 2 – Phosphor screens and pin hole 3 – Pyrometer 4 – Current transformer
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CAD Design
Time-Domain Simulations of the HeatWave Gridded Gun
Square wave grid input pulse
Emitted beam current at 20 kV
Burst mode operation of the gun
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50 ns
1 1 2005
T nsf MHz
= = =
Pulse mode (“Class-D”) operation
0.09 m
Emitter Beam out
-16 kV 0 V
Grounded Surface
Voltage Applied Surface Gap
-17 kV 0 V
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0 kV 0 V 1/gamma 1.00
0.96
0.98
0kV Potential Potential 1/gamma 0 kV 0 V
- 10kV 0 V -16 kV
0 V -17 kV -20kV
Beam Deceleration Across a Gap
Prototyping Solenoid for Test-Stand
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Maxwell - Simulations of the on-axis Field. 300 turns of 10 AWG at 16.6 A.
13.4 cm
10.4 cm
Solenoid Built In-House
http://www.lle.rochester.edu/media/publications/lle_review/documents/v133/133_07_Solid.pdf
Loaded with coil pack
Fast Grid/Mod-Anode Modulator
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1:1 Coil ratio provides summation of pulses. Divided board allows for core resetting.
Plug-in circuit boards for inductive summer modulator
http://www.lle.rochester.edu/media/publications/lle_review/documents/v133/133_07_Solid.pdf
Inductive-Adder Transformer or (Linear Transformer Driver)
Multiple Stages
Fast Grid/Mod-Anode Modulator Switch Technology based on IXYS boards with FETs capable of 1 kV at 20 A within 5 ns
Finger stock gun connector to minimize parasitics.
Capable of operating up to 30 MHz
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Secondary
Yellow – (pos) Primary 1, Green – (neg) Primary 2
Purple – Secondary
Needs scale from Charles
Constant Impedance Tunable IOT Power Extraction Circuit
0.3 m
23 Ion pump
Initial Design 44 turn primary, 4 turn secondary
Input / Output Terminals ( ) 1 o
p o gapo
Y Y jB Zωωωω ω
− = + − ≡
Admittance seen by the beam
Resonant frequency
( ) 1/22 20 0 p sL N C M Cω
− = +
( ) 1/22 2 201 /p s
R N C M C N LQ
= +
02 /Q B Y=
1 2 20 0 /Y N R M− =
Impedance at resonance presented to the beam is independent of frequency
Coupling = 0.47
Tunable Cavity with Frequency Invariant Impedance
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Design Parameters
0.249 , 23.49ssLpp uH L uH= =
Tunable High Voltage Capacitor
1.07 10.78Cp nF to pF= − −
9.8Zgap k= Ω
Alternate Transformer Designs To Improve Coupling Coefficient
25
Wide conductors strips to reduce flux leakage
Multiple secondaries connected in parallel
Conceptual System Design for a Barge with a MIG-IOT
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System Design for a Barge with a MIG-IOT
• Draw what a full system would look like for 1 tube and 1 antenna at 1 MW peak
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Tasks for Vendor of UMD MIG Gun Year - 3 Year - 4 Year - 5 1 – Create design and drawing package 2 – Manufacture MIG Gun
Experimental Program Timeline Tasks for HeatWave Labs Year - 3 Year - 4 Year - 5 1 – Manufacture gridded gun
Tasks for UMD CPB Group 3 4 5 1 – Construct and test prototype tunable cavity circuit for gridded gun and test with beam
2 – Construct and test fast RF modulator for gridded gun and test with beam
3 – Review and finalize MIG gun design with Vendor – engineering review
4 – Design and assemble fast RF modulator for MIG gun and a tunable cavity (capable of handling average power)
5 – Retrofit beam line for MIG gun 6 – Test MIG IOT
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Option Years
Where we go next • As soon as it arrives (HeatWave Labs gridded gun), we will be able to use it as a
prototyping source, to testing and optimize various subsystems
• The fast RF modulator and a beam ready prototype constant impedance cavity is under construction for the gridded gun from HeatWave Labs.
• Solenoid fields are currently being optimized for the MIG gun as well as the emitter shape. Once the initial design is optimize, we will write a DURIP proposal in order to build the gun with a vendor such as Calabazas Creek Research, Inc.
• In the 4th year, we will design and assemble a fast RF modulator capable of driving the MIG gun as well as a tunable cavity capable of handling the average power with thermal management.
• We will test the MIG IOT in the 5th year.
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