Prospects for an Inductive Output Tube (IOT) Based Source...• Introduction and Team • Why...

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

2

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

5

- 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

http://www.e2v.com/products/rf-power/inductive-output-tubes/

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.

7

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

8

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

9

Emitter

Focus

Focus

Decreased defocusing occurring at high currents Gap

Gap

Mod-Anode


No intercepted current (grid-less) Beam is controlled through a mod-anode

Beam 70 kV at 15 A = 1 MW


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

10

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.

11

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.

12

Phase-Space vs Position at Different Voltages

Deceleration of 60.7 kV


Rb/Rw = 0.81 L/Rw = 3.45

Deceleration of 60.5 kV

Deceleration of 56 kV

Gap

13

Simulated Phase-Space vs Position at Different Voltages


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

14

Beam

Emitter 0.33 m

Ion Pumps

Prototyping Studies for Subsystem Optimization using a Gridded Gun

from HeatWave Labs

15

16

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

17

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

18

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

19

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

20

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

21

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

22

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

24

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

26

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

27

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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Prospects for an Inductive Output Tube (IOT) Based Source...• Introduction and Team • Why...

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