A 650 GHz helical BWO

The operational frequency of helical vacuum electron devices has always been limited by the ability of conventional technology to fabricate very small helices, and by the difficulty of passing a meaningful current through the center of such a small structure. Microfabrication technology now offers the possibility of creating helices smaller in outside diameter than a human hair. These helices are not fabricated by wrapping wire or tape around a mandrel, they are grown. We will use such small helices to create a new class of vacuum electron devices that will operate by passing an electron beam around the outside of the helix, rather than through the center. This technology not only offers the opportunity to make meaningful incursions into a previously unused portion of the electromagnetic spectrum, it offers the possibility to do so inexpensively and in large quantities. This paper will discuss the design rationale and fabrication plan to be employed for the first device of this new class, a 650 GHz helical backward wave oscillator (BWO). A companion paper will describe the computational simulation of the 650 GHz BWO.