A 350 MHz, 200 kW CW, Multiple Beam IOT

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.

Goals of the Research • Frequency 352 MHz • Bandwidth 4 MHz • Output Power 200 kW CW • Gain 23 dB • Operating Voltage 30 kV • Efficiency 70% • Total Current 9.5 A • Number of beams 7 • Average Current per beam 1.4 A

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

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

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

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

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

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

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

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

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

HFSS Analysis of Input Cavity

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

Output Cavity Beam Tunnels Output Coupler

Output Cavity Field Plots

Output Cavity Fabrication

Output Window Water cooling Ceramic

Collector Tailpipe Collector Output coupler Output Window

Collector Simulations

Collector Thermal Analysis

Collector and Window Assembly

Solenoid and Driver 1.5 kW CW at 350 MHz

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

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

A 350 MHz, 200 kW CW, Multiple Beam IOT