Recent research and development has been incredibly successful at advancing the capabilities for vacuum electronic device (VED) sources of powerful terahertz (THz) near-THz coherent radiation, both CW or average pulsed. Currently, VED source portfolio covers over 12 orders magnitude in power (mW-to-GW) two frequency (from <; 0.1 to >; 10 THz). Further advances are still possible anticipated. They will be enabled by improved understanding fundamental beam-wave interactions, electromagnetic...

During the three decades 1980–2010, magic angle spinning (MAS) NMR developed into method of choice to examine many chemical, physical, and biological problems. In particular, a variety dipolar recoupling methods measure distances torsion angles can now constrain molecular structures high resolution. However, applications are often limited by low sensitivity experiments, due in large part necessity observing spectra low-γ nuclei such as I = 1/2 species 13C or 15N. The difficulty is still...

DNP (dynamic nuclear polarization) experiments at 5 T are reported, in which a cycoltron resonance maser (gyrotron) is utilized as 20 W, 140 GHz microwave source to perform the polarization. MAS (magic angle spinning) NMR spectroscopy with has been performed on samples of polystyrene doped free radical BDPA (\ensuremath{\alpha},\ensuremath{\gamma}-bisdiphenylene-\ensuremath{\beta}-phenylallyl) room temperature. Maximal enhancements \ensuremath{\sim}10 for $^{1}\mathrm{H}$ and...

Dynamic Nuclear Polarization (DNP) experiments transfer polarization from electron spins to nuclear with microwave irradiation of the for enhanced sensitivity in magnetic resonance (NMR) spectroscopy. Design and testing a spectrometer magic angle spinning (MAS) DNP at 263 GHz frequency, 400 MHz (1)H frequency is described. Microwaves are generated by novel continuous-wave gyrotron, transmitted NMR probe via transmission line, irradiated on 3.2 mm rotor MAS experiments. signal enhancements up...

Gyrodevice oscillators and amplifiers (or gyro-oscillators gyro-amplifiers) are being utilized in a variety of applications where high power levels required at millimeter-wave frequencies. Gyro-oscillators, developed primarily for magnetic fusion research applications, have achieved near 1 MW pulse durations excess s frequencies above 100 GHz. Continued work on these devices should enable them to achieve continuous-wave operation multimegawatt the 100-GHz 200-GHz range, thereby meeting...

The nonlinear efficiency for a gyrotron oscillator operating at harmonics of the cyclotron frequency has been calculated and is presented as function generalized parameters second through fifth harmonics. numerical results are valid wide range conditions, including voltage, current, beam radius, cavity dimensions, mode. Relatively high efficiencies found even harmonics; maximum transverse 2, 3, 4, 5 0.72, 0.57, 0.45, 0.36, respectively. calculation in terms allows straightforward design...

Abstract The coherent X-ray scattering for momentum transfer, k, between 0·025 and 15·0 Å−1 has been measured a series of sputtered amorphous Ge films prepared at various substrate temperatures, T s, 0 350°C. Differences in the radial distribution function (RDF) different s have determined by an accurate differential technique. small angle (SAS) is less than 100 electron units k < 1 Å−1. From combination SAS, RDF scanning microscope studies, it concluded that observed increase film density...

We report the observation of enhanced coherent Smith-Purcell radiation (SPR) at terahertz (THz) frequencies from a train picosecond bunches 15 MeV electrons passing above grating. SPR is more intense than other sources, such as transition radiation, by factor Ng, number grating periods. For electron that are short compared with wavelength, emission occurs, Ne, in bunch. The beam consists Nb bunches, giving an energy density spectrum restricted to harmonics 17 GHz bunch frequency, increased...

We report the short-pulse operation of a 460 GHz gyrotron oscillator both at fundamental (near 230 GHz) and second harmonic electron cyclotron resonance. During in microsecond pulse length regime with 13-kV beam voltage 110-mA current, instrument generates several watts power two modes, TE/sub 2,6,1/ 456.15 0,6,1/ 458.56 GHz. Operation including 0,3,1/ mode 237.91 2,3,1/ 233.15 GHz, is observed output powers up to 70 W. Further, we demonstrate broadband continuous frequency tuning modes over...

Dynamic nuclear polarization (DNP) transfers the large of unpaired electrons to nuclei and thus significantly enhances signal strength in magnetic resonance (NMR) spectroscopy. High frequency/field (140 GHz/5 T) DNP has been implemented solid state NMR experiments using a nitroxide radical as paramagnetic polarizing agent water:glycerol frozen solution. The 1H 13C strengths both solvent an amino acid solute have enhanced by factor 185, which represents reduction ≳102 sample size requirements...

A continuous random network (CRN) consisting of 238 tetrahedrally coordinated atoms has been constructed so as to contain only even-membered rings. The structural properties the model (density, bond-length distribution, bond-angle dihedral-angle radial distribution function) are in satisfactory agreement with experimental results for amorphous Ge, Si, and III-V compounds. present eliminates conflict between Polk CRN model, which contains approximately 50% odd-membered rings, photoemission,...

Dynamic nuclear polarization (DNP) increases the sensitivity of magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer electrons spins. The enhancement in NMR can amount a factor well above 100, enabling faster data acquisition and greatly improved measurements. With increasing fields (up 23 T) used research, required for DNP falls into THz band (140-600 GHz). Gyrotrons have been developed meet demanding specifications NMR, including power levels tens watts;...

The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. is intended to be used as submillimeter-wave source for 700-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic polarization. operates in the whispering-gallery mode TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11, 2</sub> has generated 16 W output power 13-kV 100-mA electron beam. start...

The design and the operation of a frequency-tunable continuous-wave (CW) 330-GHz gyrotron oscillator operating at second harmonic electron cyclotron frequency are reported. has generated 18 W power from 10.1-kV 190-mA beam working in TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4,3</sub> cylindrical mode, corresponding to an efficiency 0.9%. measured start oscillation current over range magnetic field values is good agreement with...

Abstract The structural properties (radial distribution function, small angle scattering, density), optical (complex dielectric function versus energy), and other characterizing parameters (scanning electron microscope examination, chemical analysis, recrystallization behaviour, transport phenomena), have been determined for a series of amorphous Ge films sputtered at different substrate temperatures. Various these (e.g. refractive index, density, room temperature conductivity) show only...

We report the observation of two-dimensional plasma filamentary arrays with more than 100 elements generated during breakdown air at atmospheric pressure by a focused Gaussian beam from 1.5-MW, 110-GHz gyrotron operating in 3-micros pulses. Each element is filament elongated electric field direction and regularly spaced about one-quarter wavelength apart plane perpendicular to field. The development array explained as result diffraction around filaments, leading sequential generation high...

A gyrotron oscillator with a single cylindrical cavity has produced output powers up to 645 kW and efficiencies 24% at 140.8 GHz, step-tunable single-mode operation between 126 243 GHz. Mode stability suppression of nearby competing modes are found persist even for in very high-order severe mode competition. These results greatly improve prospects developing cw megawat gyrotrons relevant the heating fusion plasmas.

The rate of absorption and emission radiation is calculated for two laser fields interacting with a homogeneously broadened, three-level molecular system. time-dependent Schrödinger equation used in the density matrix formalism are treated classically. fields, at frequencies ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> , off resonance by δ respectively, such that <tex...

Recent studies of 110 GHz microwave discharges in air at atmospheric pressure have demonstrated formation a large array quarter-wavelength-spaced plasma filaments. Here we present measurements showing that as is decreased from atmosphere to few torr, the discharge transitions well-defined smeared-out and finally diffuse plasma. Despite distinct nature breakdown phenomena high frequencies, dependence threshold field seen follow Paschen-type curve. Data for argon are compared with previous...

We report the experimental demonstration of a gyrotron traveling-wave-tube amplifier at 250 GHz that uses photonic band gap (PBG) interaction circuit. The achieved peak small signal gain 38 dB and 45 W output power 247.7 with an instantaneous $\ensuremath{-}3\text{ }\text{ }\mathrm{dB}$ bandwidth 0.4 GHz. can be tuned for operation from 245--256 widest 4.5 centered 253.25 was observed 24 dB. PBG circuit provides stability oscillations by supporting propagation transverse electric (TE) modes...