Theory & Simulation for Vacuum Electronic Devices :

Analysis & Simulation of Vacuum Electronic Devices:

Contributed and guided co-workers on development of several new analytical models, and computer simulation codes/ methodologies for electron optical systems microwave interaction structures, large signal analysis, PIC simulation, thermal & vibrational analysis, multi-physics simulation and optimisation for various vacuum electronic devices, such as, helix- and coupled-cavity travelling-wave tubes (TWT), planar TWTS, multi-beam klystron, gyrotron, gyro-TWT, virtual cathode oscillator (vircator), and relativistic magnetron.

Electron-optics:

• Electron Guns: 2.5-D and 3-D Electron trajectory and particle-in-cell (PIC) simulation in electro-and magneto- static fields for various types of electron guns: Pierce-, gridded-, shadow-gridded-, magnetron injection-, multi-beam- guns including the thermal effects and ion effects.

• Multistage Collectors: 2.5D trajectory simulations including the effects of multiple generations of secondaries (slow- and fast secondaries and reflected primaries) and leakage magnetic field for high efficiency multistage collectors. 3-D Trajectory Simulation and 3-D PIC simulation of symmetric/ asymmetric collectors.

• Focussing-Systems: 2.5D trajectory and 3-D PIC simulation of trajectories in electrostatic and magnetic focussing-systems. Guided students on various analytical models and codes for first cut design calculation and stability analysis of practical periodic permanent magnetic (PPM) focussing systems with single- and double-periodic variations. Designed focussing system for multi-beam device. Electrostatic focussing of single beam and multi-beam device.

Computer-Simulation Codes:

The following packages for Computer simulation of Electron guns and depressed collectors, are to his credit.

Program for Improved Electron Ray-tracing in Collectors & Electron guns (PIERCE): A fast and accurate 9-point FDM 2.5- dimensional program for high accuracy simulation of axisymmetric electron guns including grids and magnetic field, and multi- element depressed collectors. with facility for simulation of multiple generations of slow-and fast secondary electrons, and ion trajectories along with several new features was developed. The program has been extensively used by many researchers for simulation of various types of diode and gridded electron guns and collectors at CEERI, MTRDC, BEL and other institutes.

LKOBRA: A package for 3-dimensional simulation of multi-element depressed collectors was developed under an ESA contract at Engineering Department, Lancaster Uni. (UK). The package is based on a 3-D code KOBRA3 originally developed by another group. It is in use at Lancaster Uni, UK, TTE, Ulm, Germany, and ESA/ESTEC, The Netherlands.

Microwave Interaction Structures:

Guided co-workers and directly contributed in evolving simple, fast and novel geometries, analytical methods and simulation schemes for cold characteristics of interaction structures and full devices.

Helix-SWS

My group has developed analytical models for dispersion and interaction impedance characteristics of broad-band, sheath helix, tape helix and helix derived (ring-loop and ring-bar) slow-wave structures, including various types of inhomogeneous and anisotropic loading: vane-, semi-vane-, and chiral-loading; effects of dielectric loss, conductivity loss, attenuator and sever loss, meander-line resonant loss; and helix- to coaxial/waveguide couplers; coaxial windows, analysis of π-mode stop bands in asymmetric SWS. Small and large-signal analysis for broadband multi-dispersion circuits, BWO-oscillation start up conditions for uniform and step-tapered helix SWS, and ‘Modified infinite number of vanes model’ (MINV) for segment-loaded helix SWS. Methodology for 3-D electromagnetic simulation for cold characteristics, and 3D-particle-in-cell simulation for hot characteristics -determination and optimisation have been established. (codes, HFSS, MAFIA, CST etc.).

Coupled-cavity-slow-wave structure

Analytical models and 3D-simulation and cold test experiments for dispersion, impedance characteristics of single- and double- slot space harmonic coupled-cavity SWS, inverted slot-mode and inductively coupled inter-digital SWS, disc-loaded wave guides, resonant-loss loaded CC-SWS, wave guide couplers and pill-box- and resonant block- windows.

Cyclotron Resonance (Gyrotron) Devices

R & D on a new generation device based on cyclotron resonance interaction of a hollow electron beam with the transverse electric field in an overmoded open cavity, which can generate high power at mm-wave frequency, has been initiated. Analytical models and 3D-simulation and cold test experiments for dispersion and impedance characteristics of vane-loaded hollow-waveguide and coaxial waveguide gyro-TWT structures, waveguide window and coupling structures, wraparoundTE₁₀-TE₀₁ mode converters developed.

Device Modelling

Large-signal analysis and 3-D PIC modelling of helix TWT, coupled-cavity TWTs, Gyro-TWT, multi-beam klystron, relativistic magnetron, and axial-, coaxial- and multi-beam-vircator led to establishment of state-of-art design capability and highly optimised designs of microwave tubes. (using in-house/ bought out LSA codes, CST etc.).

His group introduced the use of artificial neural network method for optimisation of coupler, estimation of complex permittivity and Plasma frequency reduction in a metallic cylinder..

Plasma-antenna System:

Worked towards Ph.D. degree on theoretical and experimental study of radiation characteristics of circularly symmetric electromagnetic sources surrounded by plasma. Effects of glass tube thickness, collisions in plasma and external magnetic field, on radiation characteristics of the antenna, were also studied theoretically. A plasma laboratory was set up at BITS, Pilani for experimental studies on radiation from plasma columns excited by em sources.