1. A 350 MHz, 200 kW CW, Multiple Beam IOT Lawrence Ives, Michael Read, David Marsden, R. H. Jackson, Thuc Bui Calabazas Creek Research, Saratoga, CA. USA Takuji Kimura, Edward Eisen Communications & Power Industries, LLC. This research is supported by U.S. Department of Energy Grant DE-FG-3-07ER84876, the Naval Surface Weapons Center, and Communications & Power Industries, LLC.

2. Goals of the Research Frequency352 MHz Bandwidth4 MHz Output Power200 kW CW Gain23 dB Operating Voltage30 kV Efficiency70% Total Current9.5 A Number of beams7 Average Current per beam1.4 A

3. Design Approach and Challenges Approach Utilize existing production electron gun Arrange guns in circular pattern driving a fundamental mode output cavity Choose number of beams based on gun operation (30 kV operation) – Seven beams selected Challenges Input cavity free of parasitic modes

4. Solid Model Input Waveguide Input Cavity Electron Guns Output Cavity Collector Output Window

5. Electron Gun Uses existing production IOT electron gun Reduced cost and risk

6. Electron Gun Model for peak current = 5.6 A = 4 x average (normal ratio for IOT) Grid voltage = 0 V 2D Model Using TRAK

7. Grid Detail Grid Voltage = 0 I = 5.6 A (max) Grid reduces current below that without a grid, keeping the grid interception to ~ 0

8. Magnetics Brillouin focusing with uniform solenoid –Field set near value appropriate for max current 3D Modeling required –Used OmniTRAK

9. Input Cavity Primary challenge for MBIOT design Must drive multiple beams in parallel Avoid exciting parasitic modes Provide required coupling to input waveguide Dielectric break Tuners Cathode heater leads RF Input

10. Input Waveguide Transition Input cavity is not in vacuum, so no vacuum window is required for RF input

11. Input Circuit Input Waveguide Cavity Electron Guns HFSS Model CASCADE optimized Step transducer HFSS simulation 345.5 -30 dB

12. HFSS Analysis of Input Cavity

13. Bandwidth Analysis 348.2 MHz -30 db -20 db -10 db

14. Output Cavity Beam Tunnels Output Coupler

15. Output Cavity Field Plots

16. Output Cavity Fabrication

17. Output Window Water cooling Ceramic

18. Collector Tailpipe Collector Output Window Output coupler

19. Collector Simulations

20. Collector Thermal Analysis

21. Collector and Window Assembly

22. Solenoid and Driver 1.5 kW CW at 350 MHz

23. Summary 350 MHz 200 kW CW multiple beam IOT design complete Assembly is 95% completed Seeking additional funding to complete and test the tube

24. MBIOT Status MBIOT is ~ 95 % complete. Remaining tasks include: Rebuild output window Cold test output cavity and machine as required Braze end plates to output cavity cylinder (only remaining braze) Weld electron guns to support plate and connect heater leads Weld input cavity to high voltage ceramic and gun support plate Weld collector, output window, and input cavity/gun assembly Estimate cost to complete - $50,000