Abstract
The analysis of a Ka-band gyrotron Travelling Wave Tube (gyro-TWT) amplifier using a uniform cylindrical waveguide as its interaction circuit has been presented for the TE01 mode of operation a self-consistent nonlinear analysis in the large signal regime. The analysis predicts that the saturated peak output power of ~ 134 kW with a power conversion efficiency of ~ 22.7 %. The saturated gain has been calculated as ~ 41.3 dB for the amplifier driven by 72 kV, 8.2 A electron beam of a pitch factor 1.05. The critical interaction length of smooth wall uniform metal guide is found 10.7 cm for the stable amplifier operation. The form factor and the norm factor have also been estimated with the large signal non-linear code. Further, for 5% spread the amplifier develops the peak power of ~ 128 kW with an electronic efficiency of ~ 21.7 % and the gain of ~ 41.07 dB. These results are found to be good harmony when the beam wave interaction is studied with a commercial 3-D electromagnetic particle in cell (PIC) code. The behaviour of the beam all over the length of the interaction circuit has been monitored by calculating its energy, momentum, phase, etc. with the help of a commercial PIC code and which also in good agreement with analytical results with 1% deviation.
Highlights
High gain and wide bandwidth characteristics of the gyrotron traveling wave tube amplifiers make them attractive in the millimetre wavelength range for applications in, generation imaging radars, detection of space debris, precision tracking, high density communications, particle acceleration, materials characterization, plasma heating and solid state diagnostics, linear colliders, power beaming and electron cyclotron resonance heating of fusion plasmas, etc. [1]
A gyro-TWT amplifier using a smooth wall cylindrical waveguide is analyzed for TE01 mode of operation with the help of a self-consistent nonlinear theory and simulated using a 3-D electromagnetic particle in cell (PIC) code in order to validate the analytical findings
A saturated peak power of ~ 134 kW with an efficiency of ~ 22.7 % and a saturated gain of ~ 41.3 dB have been analytically predicted for the gyro-TWT using 72 kV, 8.2 A electron beam of 1.05 pitch factor
Summary
High gain and wide bandwidth characteristics of the gyrotron traveling wave tube (gyro-TWT) amplifiers make them attractive in the millimetre wavelength range for applications in, generation imaging radars (near 35 and 94 GHz), detection of space debris, precision tracking, high density communications, particle acceleration, materials characterization, plasma heating and solid state diagnostics, linear colliders, power beaming and electron cyclotron resonance heating of fusion plasmas, etc. [1]. The large signal operation of the gyro-TWT can be described by the following set of equations, known as pendulam equations, for the changes in electron energy, phase, and in the wave amplitude along the axis of the interaction circuit. The form factor (Ls) signifies the coupling between the cyclotron wave and the resonant waveguide mode in a gyro-TWT amplifier It depends on the transverse dimension of the arbitrary shape interaction circuit and can be written as [24]:. Where ⃗⃗⃗⃗ is the normal to the interaction circuit's cross section and is the free space wave impedance
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