According to DARPA, vacuum electron devices (VEDs) are critical components for defense and civilian systems that require high power, wide bandwidth, and high efficiency, and there are over 200,000 VEDs currently in service.
While most VEDs in common use today (traveling wave tubes (TWTs), klystrons, crossed-field amplifiers, magnetrons, gyrotrons and others) were invented in the first half of the 20th century, ongoing, intense development efforts have produced dramatic advances in their performance and reliability.
Space-qualified TWTs are used for nearly all satellite communications and are demonstrating in-orbit mean time to failure of over ten million hours with power efficiencies greater than 70%. VED amplifiers also can exhibit wide operating bandwidths of over three octaves, and high output power levels up to thousands of watts from a single device. These characteristics make vacuum electronics the technology of choice for numerous military, civilian, and commercial radio frequency (RF) and microwave systems.”
A new program called Vacuum Electronic Science and Technology or INVEST looks to build systems that support higher operation RF signals that are “louder” and thereby harder to jam and otherwise interfere with. DARPA says higher frequency operation brings with it vast swaths of previously unavailable spectrum which opens the way to more versatile communication, data transmission and other capabilities that will be beneficial in both military and civilian environments.
The INVEST program aims to strengthen the science and technology base for new generations of vacuum tubes operating at millimeter-wave frequencies above 75 GHz.
DARPA. Millimeter wave vacuum tubes, including ones like the travelling wave tube (TWT) depicted here, amplify signals by exchanging kinetic energy in the electron beam (shown as a blue line) with electromagnetic energy (shown as a wave) in the signal. This figure represents a cutaway view of a TWT with all of the critical components: electron gun, magnetic circuit, electron collector, and the windows that keep the vacuum inside the tube while letting the signals flow in and out.
The DARPA Microsystems Technology Office is soliciting fundamental research proposals in the area of vacuum electronics science and technology. Proposed research should investigate innovative approaches to modeling, advanced manufacturing, theory and design of components, and other focus areas that enable revolutionary advances in vacuum electron devices at millimeter wave (mm-wave) frequencies above 75 GHz. Specifically excluded are efforts that primarily result in evolutionary improvements to the existing state of the practice.
Research focus areas include but are not limited to the following:
Advanced modeling: High-fidelity, geometry-based, multi-physics, numerically efficient, end-to-end modeling and simulation techniques for analysis, synthesis, and optimization that lead to first pass design success. Research in this focus area should result in new concepts for linking multiple three-dimensional physical models (Maxwell’s Equations for electromagnetic effects, Lorentzian forces on electrons, diffusion equations for thermal effects, etc.) to enable simultaneous simulation of the entire range of physical processes that take place in a vacuum electron device at mm-wave frequencies.
Advanced manufacturing: Advanced manufacturing techniques for beam-wave interaction circuits and other mm-wave tube components. Research in this focus area should result in new applications of emerging technologies, such as Selective Laser Sintering (SLS) and other additive manufacturing techniques, that enable direct-from-CAD manufacturing of mm-wave VED components in appropriate materials, without the high-precision assembly and alignment requirements that are a significant component of the manufacturing cost for current vacuum electron devices.
Innovative beam-wave interaction structures: Innovative beam-wave interaction structures with wide bandwidth and high peak and average power handling capacity that are designed for manufacturability at mm-wave frequencies above 75 GHz. Research in this area should focus on configurations outside of those in common use. New ideas for increasing bandwidth and peak and average power capacity are of particular interest. Design for manufacturability is highly desirable, in particular new geometries that can take advantage of batch fabrication or advanced manufacturing techniques.
Cathode science and technology: Experimental science leading to a more complete fundamental understanding of electron emission enabling the a priori design of low-temperature (less than 800 °C), high current density (over 20 A/cm2), long-life (over 10,000 hours) cathodes. Research in this area should focus on advancing the fundamental understanding of how material properties and processes correlate with cathode performance. This understanding, coupled with experimental science for verification and validation, will lead to the capability for a priori design of cathodes with specific performance for specific applications. Of particular interest are cathodes operating at low temperature and high current density with extended lifetime.