The 0.22 THz vacuum electronic circuits fabricated by UV lithography molding and deep reactive ion etching processes are under investigation for submillimeter wave applications. Eigenmode transient simulations show that, accounting for realistic values of our currently achievable fabrication tolerances, the transmission, and dispersion properties of the operation modes of a TE-mode, staggered, double grating circuit are maintained within less than 1 dB and 2% deviation, respectively. Scanning electron microscopy and atomic force microscopy analyses of the fabricated circuit samples demonstrate that both of the microelectromechanical system fabrication approaches produce circuits with ±3–5 μm dimensional tolerance and ∼30 nm surface roughness.

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Understanding of the anomalous transport 1 attributed to short-scale length microturbulence through 2 collective scattering diagnostics is key to the development of 3 nuclear fusion energy. Signals in the subterahertz (THz) range 4 (0.1-0.8 THz) with adequate power are required to map wider 5 wavenumber regions. The progress of a joint international effort 6 devoted to the design and realization of novel backward-wave 7 oscillators at 0.346 THz and above with output power in the 1 W 8 range is reported herein. The novel sources possess desirable 9 characteristics to replace the bulky, high maintenance, optically 10 pumped far-infrared lasers so far utilized in this plasma 11 collective scattering diagnostic. The formidable fabrication 12 challenges are described. The future availability of the THz 13 source here reported will have a significant impact in the field of 14 THz applications both for scientific and industrial applications, 15 to provide the output power at THz so far not available. AQ:1 AQ:2 AQ:3 16 Index Terms-Backward-wave oscillator (BWO), double-17 corrugated waveguide (DCW), double-staggered grating (DSG), 18 plasma diagnostic, terahertz (THz).19

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This article is a detailed account of additive manufacturing (AM) processes for copper and copper alloys such as copper-chromium alloys, GRCop, oxide-dispersion-strengthened copper, copper-nickel alloys, copper-tin alloys, copper-zinc alloys, and copper-base shape memory alloys. The AM processes include binder jetting, ultrasonic additive manufacturing, directed-energy deposition, laser powder-bed fusion, and electron beam powder-bed fusion. The article presents a review of the literature and state of the art for copper alloy AM and features data on AM processes and industrial practices, copper alloys used, selected applications, material properties, and where applicable, compares these data and properties to traditionally processed materials. The data presented and the surrounding discussion focus on bulk metallurgical processing of copper components. The discussion covers the composition and performance criteria for copper alloys that have been reported for AM and discusses key differences in process-structure-property relationships compared to conventionally processed material. The article also provides information on feedstock considerations for copper powder handling.

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Vacuum electron devices are the most promising solution for the generation of watt-level power at millimeter wave and terahertz frequencies. However, the three dimensional nature of metal structures required to provide an effective interaction between an electron beam and THz signal poses significant fabrication challenges. At increasing frequency, losses present a serious detrimental effect on performance. In particular, the skin depth, on the order of one hundred nanometers or less, constrains the maximum acceptable surface roughness of the metal surfaces to be below those values. Microfabrication techniques have proven, in principle, to achieve values of surface roughness at the nanometer scale; however, the use of different metals and affordable microfabrication techniques requires further investigation for a repeatable quality of the metal surfaces. This paper compares, for the first time, the nanoscale surface roughness of metal THz waveguides realized by the main microfabrication techniques. In particular, two significant examples are considered: a 0.346 THz backward wave tube oscillator and a 0.263 THz traveling wave tube.

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