A. K. Tanwar

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.

Experimental study on 0.1 THz Clinotron

A multimode theory of resonant backward wave oscillator with inclined electron beam - Clinotron is introduced. The mechanism of the efficiency enhancement due to mode interaction is unveiled through numerical simulation. The experimental setup for 0.1 THz Clinotron is being developed and the details of each part will be presented.

Study and Development of Alloy-film Dispenser Cathodes

In this paper, the developmental work on alloy-coated cathode and thermionic emission microscope (THEM) is presented. The cathode is incorporated with potted heater assembly. A contra-wound helix filament is used to minimize inductance. The heater is potted using non-shrinkable alumina powder at elevated temperature. To minimize thermal and mechanical stresses at the heater lead, a spring (micro-helix) is incorporated which slide fits into the lead wire that is partially buried into the potting region. The above alloy of 20s:2Re:1W is chosen on the basis of work carried out at Cambridge, using auger electron spectroscopy (AES) in conjunction with THEM.

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.

Sol-gel synthesis of Sc 2 O 3 doped W nano-particle for cathode application

Sc2O3 doped W nano-powder is believed to play a dominant role for improving emission capabilities of the high current density thermionic cathodes. In this study a novel nano-particle synthesis approach was adopted in order to precisely control the particle parameters. The particle characteristics and sintering behavior has been analyzed using SEM, TEM, EDS, XRD and XPS. Uniform grain size with average particle diameter~50 nm, spherical morphology, uniform phase and homogeneous mixing of Sc2O3 doped W nano-powder was obtain which will enhance the emission current density, emission uniformity and life of the cathode.

Effect of surface roughness of high current density nano-particle cathode for terahertz vacuum devices application

High current density dispenser cathode is critical need for used in high power terahertz devices. Recently scandate cathode using nanoparticle offers very high current density more than 100 A/cm2. Fabrication of this kind of cathode is challenging issue due to its nano dimension of the particle size. One of the critical parameter is surface roughness of the emission surface. We develop dispenser cathode using tungsten nano-particle of average particle diameter ~50 nm, spherical morphology and uniform phase. In this paper we explain the effect of surface roughness on the emission current density of the dispenser cathode.

Design of depressed collector for 94 GHz CCBWO

In this paper design of a single-stage depressed collector is discussed for a 94 GHz coupled cavity back-ward wave oscillator (CCBWO). A single-stage depressed collector is designed to improve the over all efficiency of the device and better thermal management in the collector. A detailed design approach of depressed collector along with secondary electron effect and thermal analysis are discussed in the following sections.

High current density ternary-alloy-film dispenser cathode for terahertz vacuum devices

Dispenser cathode is used in microwave tubes as source of electrons. We investigate high current density emission capabilities of alloy-coated cathodes used for terahertz vacuum devices. In this paper the developmental work carried out on ternary-alloy-film cathode (2Os:2Re:1W) and the results are presented. The cathodes were tested inside a closed spaced diode and also analytical chamber containing Auger Electron Spectroscopy (AES), Thermionic Emission Microscope (THEM) facility. Emission current densities measured in the diode structure at 1300° K temperature were above 60 A/cm2. The work function was found 1.72 eV using 73% slope method. To ensure the life of the cathode accelerated life test has been carried out in closed spaced diode at 1300° K temperature.