dc.description.abstract |
In this dissertation, the development of BWOs with arbitrarily corrugated slow wave
structures (SWSs) that will provide improved efficiency with higher output power
and ease of fabrication is presented. A comprehensive theoretical formulation has
been developed in order to analyze the BWO with arbitrarily corrugated SWSs. The
chosen corrugated SWSs are, (1) trapezoidally corrugated SWS (TCSWS), (2) semicircularly
corrugated SWS (SCCSWS), (3) triangularly corrugated SWS (TrCSWS),
and (4) circular-edge disk-loaded SWS (CDSWS). The radial functions defining the
proposed SWSs have been derived in terms of Fourier series in an attempt to apply the
Rayleigh-Fourier method for the analysis. The zero-beam current dispersion characteristics
of fundamental as well as higher order TM modes have been calculated analytically
which are verified with the cold test experimental values and the numerically
obtained values using the commercial EM solver, CST. Comparisons of the analytical
and numerical results with the results found from the experiments show an excellent
agreement which provides a high degree of assurance in the validation of the developed
theory and the simulated results. Microwave radiation is generated when an electron
beam with sufficient energy and current propagates through the SWS to initiate the
instability. To study the temporal growth rate (TGR) for the fundamental TM01 mode,
the dispersion equation is solved for the beam current of 0:1 1:0kA and the beam
energy of 205665kV . For the TM01 mode, the TGR of the BWOs with the proposed
SWSs, which provides a qualitative index of the strength of the microwave generation,
is compared with those of the BWO with sinusoidally corrugated SWS (SCSWS) for
different beam parameters. The study reveals that, while the performance of SCCSWS
is significantly inferior to SCSWS, TCSWS, TrCSWS, and CDSWS; the TCSWS,
TrCSWS, and CDSWS exhibit an average of 1.48% , 1.98% , and 7.71% higher
peak TGR (PTGR) respectively, compared to conventionally used SCSWS. In order to
substantiate the improved PTGR obtained analytically, the particle-in-cell (PIC) based
simulation is performed and the time dependent output power, field analysis, and phase
space plots are studied rigorously. With a beam voltage of 341kV and a beam current
of 0:8kA, a maximum conversion efficiency of 32.82%, 16.41%, 33.74%, 51.16%, and
26.41% has been achieved for TCSWS, SCCSWS, TrCSWS, CDSWS and conventionally
used SCSWS respectively, from which it can be deduced that the BWO with the
proposed CDSWS provides maximum conversion efficiency with peak output power
of 139:56MW. Moreover, the CDSWS also provides an advantage in the fabrication
process and is less prone to RF breakdown since it has no sharp edges in the inner wall
where the electric field intensity can be infinitely high. |
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