A5051057094- Gyrotron and Vacuum Electronics Research
- Particle accelerators and beam dynamics
- Microwave Engineering and Waveguides
- Pulsed Power Technology Applications
- Photonic and Optical Devices
- Particle Accelerators and Free-Electron Lasers
- Photonic Crystals and Applications
- Metamaterials and Metasurfaces Applications
- Terahertz technology and applications
- Plasma Diagnostics and Applications
- Superconducting Materials and Applications
- Magnetic confinement fusion research
- Acoustic Wave Resonator Technologies
- Plasmonic and Surface Plasmon Research
- Plasma Applications and Diagnostics
- Advanced Antenna and Metasurface Technologies
- Superconducting and THz Device Technology
- Advanced NMR Techniques and Applications
- Antenna Design and Analysis
- Advanced Photonic Communication Systems
- Energy Harvesting in Wireless Networks
- Advanced X-ray Imaging Techniques
- Fusion materials and technologies
- Electromagnetic Simulation and Numerical Methods
- Radio, Podcasts, and Digital Media
Plasma Technology (United States)
2015-2024
Massachusetts Institute of Technology
2015-2024
Fusion Academy
2015-2024
Fusion (United States)
2015-2024
Lawrence Livermore National Laboratory
2011
IIT@MIT
2007-2010
IBM (United States)
2010
University of Stuttgart
2009
Michigan State University
2008
Oak Ridge National Laboratory
2007
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...
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...
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...
In this paper, we present the design of a microwave generator using metamaterials (MTMs) in negative index waveguide interacting with high-power electron beam. The structure is formed by inserting two MTM plates loaded complementary split-ring-resonators (CSRRs) into rectangular waveguide. Electromagnetic simulations high-frequency simulator code confirm presence TM-like mode suitable for use backward-wave oscillator (BWO). Particle-in-cell (PIC) computer simulation technology (CST) Particle...
We report the electromagnetic properties of a waveguide loaded by complementary electric split ring resonators (CeSRRs) and application in vacuum electronics. The S-parameters CeSRRs free space are calculated using HFSS code used to retrieve effective permittivity permeability an medium theory. dispersion relation with is two approaches: direct calculation theory; results good agreement. An improved agreement obtained fitting procedure for tensor gain backward wave mode CeSRR-loaded...
Metamaterials (MTMs) are structured materials with subwavelength features that can be engineered to have some unique properties not found in nature, such as negative refractive index, reversed Doppler effect, and Cherenkov radiation. Based on these novel MTMs, several important research groups made great attempts develop MTM-inspired vacuum electron devices (VEDs) accelerators. Just solid-state power innovated by incessant emerging of new semiconductor materials, VEDs also inspired MTMs very...
We present 3D electromagnetic simulations of the coupling a 250 GHz beam to sample in 380 MHz DNP NMR spectrometer. To obtain accurate results for magic angle spinning (MAS) geometries, we first measured complex dielectric constants zirconia, sapphire, and matrix material (DNP juice) from room temperature down cryogenic temperatures 220 325 with VNA up 1 THz TDS system. Simulations were carried out ANSYS HFSS code as function rotor wall (zirconia or sapphire), thickness, focusing (lens no...
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...
We report the testing of a high gradient electron accelerator with photonic-band-gap (PBG) structure. The structure confines fundamental TM(01)-like accelerating mode, but does not support higher-order modes (HOM). absence HOM is major advantage PBG accelerator, since it suppresses dangerous beam instabilities caused by wakefields. was designed as triangular lattice metal rods missing central rod forming defect confining mode and allowing to propagate along axis. design frequency six-cell...
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...
An electron beam passing through a metamaterial structure is predicted to generate reversed Cherenkov radiation, an unusual and potentially very useful property. We present experimental test of this phenomenon using intense loaded waveguide. Power levels up 5 MW are observed in backward wave modes at frequency 2.40 GHz one microsecond pulsed 490 keV, 84 A 400 G magnetic field. Contrary expectations, the output power not generated mode. Instead, presence field, which required transport beam,...
A 94-GHz overmoded traveling-wave tube (TWT) has been designed, fabricated, and successfully tested. The TWT operates in the rectangular TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> mode of cavity, while lower order modes are suppressed using selectively placed strips lossy dielectric. 87-cavity circuit was directly machined from Glidcop, a dispersion-hardened copper. tested 0.25 T solenoidal magnetic field 3-μs pulses. Operating...
We report the design and experimental demonstration of a frequency tunable terahertz gyrotron at 527 GHz built for an 800 MHz Dynamic Nuclear Polarization enhanced Magnetic Resonance (DNP-NMR) spectrometer. The is designed second harmonic (
We present the first demonstration of high-power, reversed-Cherenkov wakefield radiation by electron bunches passing through a metamaterial structure. The structure supports fundamental transverse magnetic mode with negative group velocity leading to radiation, which was clearly verified in experiments. Single 45 nC 65 MeV traversing generated up 25 MW 2 ns pulses at 11.4 GHz, excellent agreement theory. Two 85 appropriate temporal spacing 80 coherent superposition, highest rf power that...
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...