Prospects for an Inductive Output Tube (IOT) Based Source

Transcription

1 Prospects for an Inductive Output Tube (IOT) Based Source Brian Beaudoin February, Institute for Research in Electronics & Applied Physics 1

2 Introduction and Team Outline 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 2 Summary and plans

3 Graduate and Undergraduate Student Team Amith Narayan Charles Turner Connor Thompson Jayakrishnan Karakkad Nikhil Goyal Quinn Kelly 3

4 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 CERN LHC FNAL LINAC - H. Haseroth, CERN, Internal, Trevor A. Butler, FNAL-LINAC Modulator, Internal G. Clerc, JP Ichac, C. Robert, A New Generation of Gridded Tubes for Higher Power and Higher Frequencies, 17 th Particle Accelerator Conference, Vancouver, Canada,

5 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 nonuniformity 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 - G. Clerc, JP Ichac, C. Robert, A New Generation of Gridded Tubes for Higher Power and Higher Frequencies, 17 th Particle Accelerator Conference, Vancouver, Canada,

6 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 MHz CPI (VKP-9050), 90 kw CW operating at 500 MHz

7 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

8 An Initial Design Based on an Existing Emitter from HeatWave Labs Annular Beam Cathode (Emitter) Gap Focus Emitter Focus Mod-Anode Michelle Simulations No intercepted current (grid-less) Beam is controlled through a mod-anode Defocusing occurring at high currents Gap Current density? Beam guided by Solenoid 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

9 Modified Emitter Design to Increase Electrostatic Focusing in the Emitter Region Annular Beam Cathode (Emitter) Focus Gap Emitter Focus No intercepted current (grid-less) Beam is controlled through a mod-anode Gap Mod-Anode Decreased defocusing occurring at high currents Beam guided by Solenoid Beam 70 kv at 15 A = 1 MW 9 - Jayakrishnan A. Karakkad, Brian L. Beaudoin, John C. Rodgers, Gregory S. Nusinovich, Thomas M. Antonsen Jr., IVEC 2016.

10 Time-Domain Simulation of the MIG Pulse mode ( Class-D ) operation Emitted current of 15 A at a 60 ns pulse width Beam Current (A) Beam Current vs. Time 60 ns 15 A 0 A Square wave input pulse driving modanode Mod-Anode swings from cutoff kv to saturation kv Mod-Anode Voltage (V) Mod-Anode Voltage vs. Time kv kv 10 - Jayakrishnan A. Karakkad, Brian L. Beaudoin, John C. Rodgers, Gregory S. Nusinovich, Thomas M. Antonsen Jr., IVEC 2016.

11 Limitations of Beam Deceleration across a Resonant circuit Gap R b /R w = 0.9 Fixed z/l = 1 L = R w Maximum voltage also decreases as the ratio of beam radius (R b ) to pipe radius (R w ) decreases Gregory S. Nusinovich, Connor Thompson, Brian L. Beaudoin, Jayakrishnan A. Karakkad, Thomas M. Antonsen Jr., IVEC 2016.

12 Phase-Space vs Position at Different Voltages R b /R w = 0.81 L/R w = 3.45 Deceleration of 60.5 kv Deceleration of 56 kv Deceleration of 60.7 kv Gap 12 - Gregory S. Nusinovich, Connor Thompson, Brian L. Beaudoin, Jayakrishnan A. Karakkad, Thomas M. Antonsen Jr., IVEC 2016.

13 Simulated Phase-Space vs Position at Different Voltages Theoretical Efficiency 5.2keV η = kev η = Gregory S. Nusinovich, Connor Thompson, Brian L. Beaudoin, Jayakrishnan A. Karakkad, Thomas M. Antonsen Jr., IVEC 2016.

14 Conceptual Drawings of the UMD-MIG 0.33 m Emitter 0.36 m Beam Ion Pumps Lawrence Ives of Calabazas Creek Research, Inc. Proposed cost ~ $245k / tube with a spare emitter Proposed timeframe ~ 9 months 14

15 Prototyping Studies for Subsystem Optimization using a Gridded Gun from HeatWave Labs 15

16 Progress on HeatWave Labs Prototyping Gun being manufacturing by HeatWave Labs. Gridded Gun Simulation of Solenoid Field Emitter Beam Specifications Cathode voltage: 20 kv Beam current: 3.3-5A Intercepted current Grid drive: +235 v Perveance: 2µPervs Iinter = 0.06 Ib Macro Pulse width: 100µs max Duty cycle: 0.04 max (or 400Hz) Grid power dissipation: 3 W max R Beam Profile (mm) Simulation Radius vs. Axial Position Axial Position (mm)

17 Prototyping Test Stand CAD Design Vacuum Chamber Controls and Scopes Diagnostics include: 1 Pressure gauge 2 Phosphor screens and pin hole 3 Pyrometer 4 Current transformer Heater and Power Supplies 17

18 Time-Domain Simulations of the HeatWave Gridded Gun Square wave grid input pulse Pulse mode ( Class-D ) operation 50 ns Emitted beam current at 20 kv Burst mode operation of the gun 1 1 T = 200ns f = 5MHz = 18

19 Beam Deceleration Across a Gap 0.09 m Emitter Grounded Surface Gap Voltage Applied Surface Beam out /gamma V 1/gamma 0 kv 0 V Potential 0 kv Potential 0kV V -16 kv 0 V -16 kv - 10kV V -17 kv 0 V -17 kv -20kV 19

20 Prototyping Solenoid for Test-Stand Solenoid Built In-House Maxwell - Simulations of the on-axis Field. 300 turns of 10 AWG at 16.6 A cm 10.4 cm Loaded with coil pack 20

21 Fast Grid/Mod-Anode Modulator Inductive-Adder Transformer or (Linear Transformer Driver) Plug-in circuit boards for inductive summer modulator 1:1 Coil ratio provides summation of pulses. Divided board allows for core resetting. Multiple Stages 21

22 Fast Grid/Mod-Anode Modulator Switch Technology based on IXYS boards with FETs capable of 1 kv at 20 A within 5 ns Capable of operating up to 30 MHz Secondary Yellow (pos) Primary 1, Green (neg) Primary 2 Finger stock gun connector to minimize parasitics. Purple Secondary Needs scale from Charles 22

23 Constant Impedance Tunable IOT Power Extraction Circuit Initial Design 44 turn primary, 4 turn secondary Input / Output Terminals 0.3 m Ion pump Coupling = 0.47 Admittance seen by the beam ω ω o 1 Yp ( ω) = Yo + jb Z gap ωo ω Resonant frequency 2 2 ( ) 1/2 ω0 = L0 NCp MC + s R = 1 ( NCp + MCs) / NL Q Q= 2 B/ Y 0 Impedance at resonance presented to the beam is independent of frequency Y N R M 1 2 / 2 0 = /2

24 Tunable Cavity with Frequency Invariant Impedance Design Parameters Zgap = 9.8kΩ Lpp = uh, L = 23.49uH Cp = 1.07nF to 10.78pF ss Tunable High Voltage Capacitor 24

25 Alternate Transformer Designs To Improve Coupling Coefficient Wide conductors strips to reduce flux leakage Multiple secondaries connected in parallel 25

26 Conceptual System Design for a Barge with a MIG-IOT 26

27 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

28 Experimental Program Timeline Tasks for HeatWave Labs Year - 3 Year - 4 Year Manufacture gridded gun Tasks for UMD CPB Group 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 Option Years Tasks for Vendor of UMD MIG Gun Year - 3 Year - 4 Year Create design and drawing package 2 Manufacture MIG Gun 28

29 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 4 th 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 5 th year. 29