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...

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...

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...

We report the design and experimental demonstration of a gyrotron oscillator using photonic-band-gap (PBG) structure to eliminate mode competition in highly overmoded resonator. The PBG cavity supports ${\mathrm{TE}}_{041}$-like at 140 GHz is designed have no competing modes over minimum frequency range $\ensuremath{\delta}\ensuremath{\omega}/\ensuremath{\omega}$ $30%$ about mode. Experimental operation 68 kV 5 A produced 25 kW peak power No other were observed full predicted operating...

We present the design and experimental results of a novel quasioptical gyrotron traveling-wave tube (gyro-TWT) amplifier at 140 GHz. The gyro-TWT produced up to 30 kW peak power in 2 micros pulsed operation 6 Hz achieving gain 29 dB, efficiency 12%, bandwidth 2.3 device was operated very higher-order mode an open interaction structure, namely, confocal waveguide. diffraction loss from sidewalls waveguide used suppress competition this highly overmoded circuit resulting stable single-mode...

Regular two-dimensional plasma filamentary arrays have been observed in gas breakdown experiments using a pulsed 1.5 MW, 110 GHz gyrotron. The gyrotron Gaussian output beam is focused to an intensity of up 4 MW/cm2. filaments develop array with spacing about one quarter wavelength, elongated the electric field direction. was imaged photodiodes, slow camera, which captures entire event, and fast camera 6 ns window. These diagnostics demonstrate sequential development propagating back toward...

This contribution addresses four potential misconceptions associated with high-resolution dynamic nuclear polarization/magic angle spinning (DNP/MAS) experiments. First, spectral resolution is not generally compromised at the cryogenic temperatures which DNP experiments are performed. As we demonstrate a modest field of 9 T (380 MHz 1H), 1 ppm linewidths observed in DNP/MAS spectra membrane protein its native lipid bilayer, and <0.4 reported crystalline peptide 85 K. Second, address concerns...

We have derived the global band gaps for general two-dimensional (2D) photonic gap (PBG) structures formed by square or triangular arrays of metal posts. Such PBG many promising applications in active and passive devices at microwave, millimeter wave, higher frequencies. A coordinate-space, finite-difference code, called structure simulator (PBGSS), was developed to calculate complete dispersion curves lattices a series values ratio post radius (r) spacing (a). The fundamental frequency were...

A linearly polarized (LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mn</sub> ) mode basis set for oversized, corrugated, metallic waveguides is derived the special case of quarter-wavelength-depth circumferential corrugations. The relationship between LP modes and conventional (HE , EH TE xmlns:xlink="http://www.w3.org/1999/xlink">0n</sub> TM corrugated guide shown. loss in a gap or equivalent miter bend waveguide calculated single-mode...

We investigate nitrogen substitution defects, also known as P1 centers, in type 1b diamonds a source of electron spin polarization that is readily transferred to 13C nuclear spins within the diamond matrix at 14 Tesla by dynamic (DNP) room temperature down 35 K. The goal was obtain quantitative model for clustered centers generated under high pressure and (HPHT). study relied on frequency-stepped measurements DNP profiles magic angle spinning (MAS) using mm-wave output frequency-tunable...

The effect of spatial dispersion on the electromagnetic properties a metamaterial consisting three-dimensional mesh crossing metallic wires is reported. effective dielectric permittivity tensor epsilon(ij)(omega, k) wire calculated in limit small wavenumbers. procedure for extracting from omega versus k dependence waves propagating bulk developed. These modes are identified as similar to longitudinal (plasmon) and transverse (photon) plasma. Spatial found have most dramatic surface that...

The operating characteristics of a 140-GHz 14-W long pulse gyrotron are presented. device is being used in dynamic nuclear polarization enhanced magnetic resonance (DNP/NMR) spectroscopy experiments. yields 14 W peak power at 139.65 GHz from the TE(0,3) mode using 12.3-kV 25-mA electron beam. Additionally, up to 12 has been observed TE(2,3) 136.90 GHz. A series converters transform TE(1,1) mode. Experimental results compared with nonlinear simulations and show reasonable agreement....

The theory, design, and experimental results of a wideband 140-GHz 1-kW pulsed gyro-traveling-wave amplifier (gyro-TWA) are presented. gyro-TWA operates in the HE(06) mode an overmoded quasi-optical waveguide using gyrating electron beam. electromagnetic interaction design processes, procedures described detail. At 37.7 kV 2.7-A beam current, experiment has produced over 820 W peak power with -3-dB bandwidth 0.8 GHz linear gain 34 dB at 34.7 kV. In addition, 1.5 (1.1%) 570 from 38.5-kV 2.5-A...

Following the understanding of cold atmospheric plasma jet control, optimization parameters for biomedical applications has become an important area research in field plasma-based cancer treatment. A real-time feedback signal is usually required by a control algorithm, such as self-adaptive jet, which designed to automatically self-optimize its adapt variety and situations. In this paper, we introduce potential replacing cell viability or stress assay with electrochemical impedance...

An experimental study of picosecond pulse amplification in a gyrotron-traveling wave tube (gyro-TWT) has been carried out. The gyro-TWT operates with 30 dB small signal gain near 140 GHz the ${\mathrm{HE}}_{06}$ mode confocal waveguide. Picosecond pulses show broadening and transit time delay due to two distinct effects: frequency dependence group velocity cutoff narrowing by finite bandwidth 1.2 GHz. Experimental results taken over wide range parameters good agreement theoretical model...

The ITER electron cyclotron heating (ECH) transmission lines (TLs) are 63.5-mm-diam corrugated waveguides that will each carry 1 MW of power at 170 GHz. TL is defined here as the waveguide system connecting gyrotron mirror optics unit (MOU) to entrance ECH launcher and includes miter bends other components. losses on have been calculated for four possible cases corresponding having HE11 mode purity input 100, 97, 90, 80%. due coupling, ohmic, conversion loss evaluated in detail using a...

We present the theoretical design and cold test of a 17 GHz photonic band gap (PBG) cavity with improved coupling from an external rectangular waveguide. The PBG is made triangular lattice metal rods defect (missing rod) in center. ${\mathrm{TM}}_{010}$-like mode was chosen as operating mode. Experimental results are presented demonstrating that critical into can be achieved by partial withdrawal or removal some lattice, result agrees simulations. A detailed accelerator structure compared...