Upper-surface-blowing flow-turning performance

Jet exhaust flow-turning characteristics were determined for systematic variations in upper-surface blowing exhaust nozzles and trailing-edge flap configuration variables from experimental wind-off (static) flow studies. For conditions with parallel flow exhausting from the nozzle, jet height (as indicated by nozzle exit height) and flap radius were found to be the most important parameters relating to flow turning. Nonparallel flow from the nozzle, as obtained from an internal roof angle and/or side spread angle, had a large favorable effect on flow turning. Comparisons made between static turning results and wind tunnel aerodynamic studies of identical configurations indicated that static flow-turning results can be indicative of wind-on powered lift performance for both good and poor nozzle-flap combinations but, for marginal designs, can lead to overly optimistic assessment of powered lift potential

Cylindrical, periodic surface lattice — theory, dispersion analysis, and experiment

A two-dimensional surface lattice of cylindrical topology obtained via perturbing the inner surface of a cylinder is considered. Periodic perturbations of the surface lead to observation of high-impedance, dielectric-like media and resonant coupling of surface and non-propagating volume fields. This allows synthesis of tailored-for-purpose "coating" material with dispersion suitable, for instance, to mediate a Cherenkov type interaction. An analytical model of the lattice is discussed and coupled-wave equations are derived. Variations of the lattice dispersive properties with variation of parameters are shown, illustrating the tailoring of the structure's electromagnetic properties. Experimental results are presented showing agreement with the theoretical model

Theory and simulations of a gyrotron backward wave oscillator using a helical interaction waveguide

A gyrotron backward wave oscillator (gyro-BWO) with a helically corrugated interaction waveguide demonstrated its potential as a powerful microwave source with high efficiency and a wide frequency tuning range. This letter presents the theory describing the dispersion properties of such a waveguide and the linear beam-wave interaction. Numerical simulation results using the PIC code MAGIC were found to be in excellent agreement with the output measured from a gyro-BWO experiment

A cusp electron gun for millimeter wave gyrodevices

The experimental results of a thermionic cusp electron gun, to drive millimeter and submillimeter wave harmonic gyrodevices, are reported in this paper. Using a "smooth" magnetic field reversal formed by two coils this gun generated an annular-shaped, axis-encircling electron beam with 1.5 A current, and an adjustable velocity ratio alpha of up to 1.56 at a beam voltage of 40 kV. The beam cross-sectional shape and transported beam current were measured by a witness plate technique and Faraday cup, respectively. These measured results were found to be in excellent agreement with the simulated results using the three-dimensional code MAGIC

The development of a laser-driven spin-polarized dieuterium target

As an alternative to standard technique for producing a polarized deuterium target, we are developing an optically pumped spin-polarized deuterium gas target for use in the Soviet VEPP-3 electron storage ring. We polarize deuterium through spin exchange with an optically pumped alkali gas in storage cell. There are many important factors affecting the deuterium polarization, two of which are the phenomenon of radiation trapping, and coverage of the Doppler-broadened absorption peaks of the alkali. A technique for determining the amount of polarization of deuterium in the cell is also mentioned. 5 refs

On the structure of non-full-rank perfect codes

The Krotov combining construction of perfect 1-error-correcting binary codes from 2000 and a theorem of Heden saying that every non-full-rank perfect 1-error-correcting binary code can be constructed by this combining construction is generalized to the $q$-ary case. Simply, every non-full-rank perfect code $C$ is the union of a well-defined family of $\mu$-components $K_\mu$, where $\mu$ belongs to an "outer" perfect code $C^*$, and these components are at distance three from each other. Components from distinct codes can thus freely be combined to obtain new perfect codes. The Phelps general product construction of perfect binary code from 1984 is generalized to obtain $\mu$-components, and new lower bounds on the number of perfect 1-error-correcting $q$-ary codes are presented.Comment: 8 page

Wind tunnel investigation of a large-scale semispan model with an unswept wing and an upper-surface blown jet flat

An investigation of the static longitudinal aerodynamic characteristics of a large-scale semispan model with an unswept wing and an upper-surface blown jet flap for lift augmentation was conducted in the Langley full-scale tunnel. The wing had an aspect ratio of 7.8 (3.9 for the semispan) and a simulated turbofan engine mounted ahead of and above the wing in a nacelle with a rectangular-exit nozzle. The flap system had three spanwise flap segments: (1) an inboard plain flap located behind the engine and having a large radius of curvature to provide a smooth upper surface to enhance the turning of the jet sheet, (2) a double-slotted midspan flap, and (3) a drooped aileron equipped with blowing boundary-layer control. The wing was also equipped with a full-span leading-edge Krueger flap with blowing boundary-layer control. In addition to the aerodynamic measurements, noise measurements were also included in the investigation for positions above and below the wing

Additive manufacturing method of prototyping novel mm-wave and THz sources

To rapidly prototype novel mm-wave and THz sources there is a requirement to create intricate structures to produce and radiate electromagnetic fields. The motivation for this work is to create improved electron-beam-driven, vacuum electronic mm-wave and sub-THz sources by exploiting dispersion engineering. Although such structures can be manufactured by other techniques, additive manufacturing has proven to be quick, reliable and cost-effective. This research is allowing the prototyping of novel mm-wave and sub-THz coherent sources

Excitation and coupling of volume and surface fields on complex electrodynamic surfaces at Mm-wave and THz frequencies

The analytical theory describing the resonant excitation and coupling of volume and surface fields on the surface of two-dimensional complex electrodynamic structures is presented. The theoretical analysis is valid over a broad frequency spectrum from mm-wave frequencies through THz and even optical frequencies. An experimental study of planar periodic structures has been carried out using a vector network analyser calibrated to operate in the 140-220 GHz frequency range. Experimental results compare resonant eigenmode formation in two periodic surface lattice structures designed to operate within the 140-220 GHz frequency band; one periodic surface lattice etched onto a metal-backed substrate and the other arranged to have an equivalent air separation. Dispersion diagrams derived from the analytical theory are presented. The results and theory are fundamental to some of the routes to the innovation of high-power, mm-wave and THz sources, solar cells, and novel sub-wavelength absorbers

Broadband amplification of low-terahertz signals using axis-encircling electrons in a helically corrugated interaction region

Experimental results are presented of a broadband, high power, gyrotron traveling wave amplifier (gyro-TWA) operating in the (75–110)-GHz frequency band and based on a helically corrugated interaction region. The second harmonic cyclotron mode of a 55-keV, 1.5-A, axis-encircling electron beam is used to resonantly interact with a traveling TE21-like eigenwave achieving broadband amplification. The gyro-TWA demonstrates a 3-dB gain bandwidth of at least 5.5 GHz in the experimental measurement with 9 GHz predicted for a wideband drive source with a measured unsaturated output power of 3.4 kW and gain of 36–38 dB. The approach may allow a gyro-TWA to operate at 1 THz