Takuji Kimura

Demonstration of a High Power, Wideband 220-GHz Traveling Wave Amplifier Fabricated by UV-LIGA

We present the first vacuum electronic traveling wave amplifier to incorporate an interaction circuit fabricated by ultraviolet (UV) photolithography and electroforming, demonstrating over 60 W of output power at 214.5 GHz from a 12.1 kV, 118 mA electron beam. The tube also achieved an instantaneous bandwidth of ~15 GHz in G-band in the small signal regime. The all-copper circuit was fabricated in two layers using a UV-transparent polymer monofilament embedded in the photoresist to form the beam tunnel prior to electroforming. Effects arising from fabrication errors and target tolerances are discussed. This microfabrication technique and demonstration paves the way for a new era of vacuum electron devices that could extend into the 1-2 THz range with advances in high-current-density electron guns.

8.3: A high aspect ratio, high current density sheet beam electron gun

A beamstick for demonstration of a 25∶1 aspect ratio, 750 A/cm² current density sheet beam for DARPAs HiFIVE project will be described.

Development of a 220 GHz 50 W sheet beam travelling wave tube amplifier

We report on progress in developing a travelling wave tube amplifier with significant gain and power at 220 GHz. This paper provides an overview of the program, describing fabrication and test of slow-wave structures with bandwidths exceeding 50 GHz centered at 220 GHz, the production of a sheet electron beam, development of a solid state preamplifier delivering 50 mW to the tube with > 17 dB of gain and beam-wave simulation of the entire circuit leading to expected output powers of over 50 W. Two further papers from the group are also submitted to IVEC: from UC Davis describing the interaction structure fabrication and hot test, and from CPI describing the sheet electron beam, TWT design and beam - wave simulations. The tube is currently under test and results will be reported in this paper.

1.3: 220 GHz 50 W sheet beam travelling wave tube amplifier

In this paper we report on a development program aimed at producing a travelling wave tube amplifier with significant gain and power at 220 GHz in a compact and lightweight package. This paper provides an overview of the program, describing development of nanoparticle scandate cathodes with current densities exceeding 100 A/cm2, MEMS fabrication and test of mm-wave waveguides and slow-wave structures with bandwidths exceeding 50 GHz centered at 220 GHz, and the production of a sheet electron beam with a current density exceeding 230 A/cm2 and an aspect ratio of 26∶1. These components may allow us to produce a 220 GHz, 50W high power amplifier with a hot bandwidth of > 20 GHz and a power-bandwidth product > 1000 W-GHz.

Design and fabrication of components for a 220 GHz 50 W sheet beam travelling wave tube amplifier

A sheet beam traveling-wave tube amplifier is currently being developed under the DARPA HiFIVE program. The device is designed to achieve over 50 W output power at 220 GHz with a power-bandwidth product exceeding 1,000 W-GHz. This paper will report on the design and fabrication status of the electron gun, RF circuit, and RF window with emphasis on simulation of beam-wave interaction using the MAGIC-3D code.

P4-2: Permanent magnet for HiFIVE sheet beam transport

A permanent magnet structure has been successfully designed and fabricated for the HiFIVE program. The design produces a peak field of 0.75 T within a gap length of 2.5 cm.

Performance of a Nano-CNC Machined 220-GHz Traveling Wave Tube Amplifier

We report on hot test measurements of a wide-bandwidth, 220-GHz sheet beam traveling wave tube amplifier developed under the Defense advanced research projects agency (DARPA) HiFIVE program. Nano-computer numerical control (CNC) milling techniques were employed for the precision fabrication of double vane, half-period staggered interaction structures achieving submicrometer tolerances and nanoscale surface roughness. A multilayer diffusion bonding technique was implemented to complete the structure demonstrating wide bandwidth (>50 GHz) with an insertion loss of about −5 dB achieved during transmission measurements of the circuit. The sheet beam electron gun utilized nanocomposite scandate tungsten cathodes that provided over 438-A/cm2 current density in the 12.5:1 ratio sheet beam. An InP HBT-based monolithic microwave integrated circuit preamplifier was employed for TWT gain measurements in the stable amplifier operation region. In the wide-bandwidth operation mode (for gun voltage of 20.9 kV), a gain of over 24 dB was measured over the frequency range of 207–221 GHz. In the high-gain operation mode (for gun voltage of 21.8 kV), over 30 dB of gain was measured over the frequency range of 197–202 GHz. High-power tests were conducted employing an extended interaction klystron.

Modeling of an inductive output tube with the MAGIC simulation code

We describe the simulation of an inductive output tube (IOT) using the particle-in-cell code MAGIC. Simulations were performed to analyze three basic processes in an IOT: formation of bunched electrons beams from a gridded electron gun, interaction between bunched beams and rf field in a resonator, and spent beam collection with a multi-stage depressed collector. There is excellent agreement between simulation results and experimental data.

Performance results of a 1.3 GHz 100 kW CW IOT

The successful performance results of an inductive output tube (IOT) operating at 1.3 GHz and 100 kW CW are summarized and compared with design requirements. The IOT system designs needed to insure reliable operation at this high power and frequency necessitated a new IOT design platform. The key platform design enhancements are also described.

A 350 MHz, 200 kW CW, multiple beam IOT

Design is complete and fabrication and assembly are nearing completion on a 350 MHz, 200 kW CW, multiple beam inductive output tube (MBIOT). Seven electron guns in a circular array will be driven by a single input cavity. RF power is generated in a single, fundamental mode, output cavity. The device is predicted to achieve approximately 70% efficiency with 23 dB gain.