A. Srivastava

Superradiant terahertz Smith-Purcell radiation from surface plasmon excited by counterstreaming electron beams

The authors show that evanescent tunneling transmission of effective surface plasmon polaritons between two counterstreaming electron beams noticeably increases Smith-Purcell radiation (SPR) intensity by about two orders of magnitude as well as lower its transition threshold from a spontaneous emission to a stimulated one. An emission mechanism of the superradiant SPR is theoreticallyanalyzed by the dielectric conversion of the structured metal surface and the boundary matching condition of Maxwell’sequations in comparison with numerical simulations.

High order mode oscillation in a terahertz photonic-band-gap multibeam reflex klystron

TM330-like higher order mode was excited in a multibeam reflex klystron oscillator employing a hybrid photonic-band-gap (PBG) cavity using a three-dimensional particle-in-cell simulation. One side of a conventional metal cavity was replaced with a dielectric photonic crystal lattice to form a hybrid PBG resonator that uses lattice band-gap effects resulting in a more uniform field of a higher order mode as well as the exclusion of some conventional-cavity-type modes, thereby reducing mode competition. Simulated reflex klystron in the hybrid PBG cavity produced an output power much higher than could be delivered in a conventional metal cavity.

Development of High-Current Sheet Beam Cathodes for Terahertz Sources

Generation of a sheet beam directly from a scandia-doped dispenser cathode has been investigated and optimized by means of beam-profile simulations and measurements. Rectangular beams 600 mum wide and 100 mum thick with current densities over 50 A/cm2 have been generated. The beams are stable for at least several hundred hours with the cathodes operating at 950degCb, making them promising candidates for application in the next generation of terahertz vacuum electron devices such as a 0.5-THz superradiant Smith-Purcell radiation source.

Broadband THz vacuum window using impedance matching approach

A practical pillbox window design was performed using impedance matching approach for use in THz vacuum electron devices. The fabricated W-band miniature window assembly showed broad frequency band ∼ 8 GHz for VWSR less than 1.22.

100GHz LIGA-fabricated coupled-cavity device

This abstract describes the design, fabrication and testing of microfabricated 100GHz coupled-cavity backward wave oscillator (CCBWO), which is operated in space harmonics −1 at 12 kV and 50 mA with round-beam radius 0.18 mm. The RF performance has studied using 3-D electromagnetic field simulator and particle-in-cell code. The cold-test assembly has been fabricated. The complete device assembly for hot-test is under fabrication. Experimental results will be presented.

Development of high current density sheet beam electron gun for Terahertz devices

The development of high current density sheet beam electron gun for Terahertz devices is carried-out. It operates at beam voltage of 12 kV and perveance 0.0136 mup to meet ours requirement of high beam current density 100 A/cm2 and low emittance 0.068 pi-mm-mrad at the beam-waist position. Currently, mentioned gun is being fabricated. Work has been initiated to test the performance of Scandate cathode using anode-aperture mapping. Current density of 50 A/cm2 has been ensured across the beam cross-section of 100 times 600 mum2.

Experimental Investigation of 95GHz Folded Waveguide Backward Wave Oscillator Fabricated by Two-Step LIGA

Most recently, 95GHz three-dimensional folded waveguide structure including the electron beam-tunnel is completely microfabricated by two-step deep-etch X-ray lithography (X-ray LIGA). The precision and positional tolerance of the circuit elements are respectively 2mum and 2-3 mum. We experimentally measured its dispersive and attenuative properties through scattering matrices and compare them to analytical and numerical calculations. The MAGIC3D simulation numerically predicted the folded waveguide BWO (FWBWO) has start-oscillation current of 30mA and produces output power of 5 Watts at the beam condition of about 12kV and 50mA. Currently, we prepare experiment of the FWBWO equipped with the electron gun

Micro-fabricated millimeter wave vacuum electronic devices

0.1 THz Coupled Cavity Backward-wave Oscillator (CCBWO) is being developed utilizing two-step X-ray lithography. The characteristics of this 0.1 THz CCBWO are investigated through cold and hot tests.

MEMS applied backward-wave oscillator for 0.1 THz

The microfabrication of a backward-wave oscillator is presented for a compact, high-power source in the terahertz range of electromagnetic spectrum. One of Micro-Electro-Mechanical Systems (MEMS) technologies, a deep reactive ion etching (DRIE), was employed and achieved the fully 3-dimensional accuracy of coupled cavities operating at 0.1 THz. The prediction and measurement on the scattering parameter of the interaction circuit showed a good agreement.

Experimental Study on Electron Guns with High Current Density Beam for THz devices

The experimental study on electron guns with high current density beam for THz devices is carried out. A thermionic electron gun is designed and the fabrication is underway. The current density requirement at the circuit is >50 A/cm2 for 0.1 THz LIGA fabricated devices [1]. A rectangular sheet electron beam for 0.5THz needs to meet the beam current density requirement of >150 A/cm2 [2].