The plasma-assisted slow wave oscillator (PASOTRON) is a high power microwave source in which the electron beam in the interaction region is confined by the background plasma. The plasma is generated by impact ionization of background gas with the electron beam. A model has been developed for temporal evolution of Argon plasma in pasotron device. In this model, we consider electron beam of energy E interacting with Argon gas. The resulting ionization creates quasi neutral argon plasma composed of argon Ar atoms, singly ionized ions Ar+1 and electrons having energy from 0 to E. Electron impact excitation, ionization, radiative decay, radiative recombination and three body recombination processes are considered in this model. Population of ground and excited states of argon atom, ground state of argon ion as well as the population of electron energy groups is calculated by solving time dependent rate equations. Temporal evolution of electron beam generated plasma is given.

Cyclotron emission from a neutralized, large orbit (LO), and finite thickness monochromatic electron beam in the presence of a right hand circularly polarized field of a plane electromagnetic wave is studied. Trajectories of N = 50000 electrons whose gyration centers are randomly distributed within a circle of radius Delta, as well as their initial position that too are randomly located on their LOs, are followed. A restoring force caused by neutralizing ions is effective for electrons leaving the outer or the inner radii of the finite thickness beam. This force is introduced by a phenomenological potential well in the radial directions as was done previously for an infinitesimally thick beam [J. Plasma Phys. 73, 523 (2006)]. It is shown that for the beams having high density, the Cherenkov instability in the azimuthal direction (CIAD) with omega < <(Omega)over tilde> + k(z)V(z) causes the excitation of microwaves. With an increase in the beam thickness, the CIAD decreases and finally stops. Beyond this thickness, the cyclotron maser instability for omega > (Omega) over tilde + k(z)V(z) causes the generation of microwaves.

This paper represents the comparison of periodic permanent magnet (PPM) and solenoid focusing for dual anode multi-beam electron gun using OPERA3D code. The electron gun has been operated at 6 kV having 75 mA beam current with 0.45 mm beam waist radius. The design has an additional feature of cathode protection from ion bombardment with the application of extra ion barrier anode.

The design of face cooled double disc window for 42 GHz, 200 kW Gyrotron has been carried out using the CST microwave studio. In this design double discs D1 and D2 of diameter 85 mm and thickness 3.2 mm sapphire window and spacing of discs 2.7 mm have been used in the simulation and sapphire discs are face cooled by Coolant FC-75. The return loss (S11) and transmission loss (S21) of the 42 GHz Gyrotron window have been found -40.3 dB and -0.04 dB respectively. The double disc face cooled structure causes power loss in two discs. In addition, loss in the coolant also has to be taken into account. However, as far as cooling of dielectric is concerned this design is the most effective. The reflection and absorption of RF power depends on the dielectric properties of sapphire as well as coolant liquid. The window geometrical parameters are optimized considering the minimum return loss and the minimum insertion loss by using CST microwave studio. The thermal design of the face cooled window during extreme case of operation, i.e. at saturation has been carried out using ANSYS software and discussed in the paper. The temperature range on the sapphire disc surface has been found to be 35 0 C - 80 0 C. The temperature range on the window disc surface has been found satisfactory. The RF window optimized design allows low heat loads in the ceramic and consequently low temperature increase and low stresses. The power handing capacity of face cooled window has been determined by ANSYS. This design of RF window is capable of handling the thermal and mechanical loading in a 200 kW output power.

This paper represents the thermal analysis of a multi-beam electron gun collector and the effect of different types of grooves on the collector temperature has also been analyzed. The design of the grooves has been optimized to enhance the efficiency of the collector using mixed (axial and radial) grooves. Finite element analysis codes OPERA 3D, ANSYS and CST have been used for the thermal study. The values of the water flow rate and the hydraulic diameter of the outer jacket have been optimized.

In this paper, the design of a Ka-band periodically ceramic loaded gyro-TWT amplifier has been carried out. The design predict that the interaction structure can produce more than 80 kW output power, 50 dB saturated gain, and 3 dB bandwidth for 65 kV and 5A electron beam with velocity ratio (alpha) of 1.2. This paper describes the design and simulation of a high performance 35 GHz TE01 mode gyro-TWT that applies the same technique of employing a periodic dielectric loaded interaction structure to achieve stability and wide bandwidth. The design of input coupler with loaded interaction structure for Ka-band Gyro-TWT has been carried out using ANSOFT HFSS. The return loss (S-11) and transmission loss (S-21) of the Ka-band gyro-TWT input coupler have been found to be -27.3 dB and -0.05 dB, respectively. The design of output window for Ka-band Gyro-TWT has been carried out using CST MICROWAVE STUDIO. (C) 2013 AIP Publishing LLC.

The design of input coupler with loaded interaction structure for Ka-band gyro traveling wave tube (gyro-TWT) has been carried out using Ansoft HFSS to operate in the TE11 mode. The return loss (S11) and transmission loss (S21) of the Ka-band gyro-TWT input coupler have been found −27.3 and −0.05 dB respectively. The design of output window for Ka-band gyro-TWT has been carried out using CST microwave studio. In this paper thermal analysis of the input coupler for Ka-band gyro-TWT has also been carried out using ANSYS software. In the simulation results, the temperature on the ceramic disc of window does not exceed 80 °C and found in safe limit. The optimized design of input and output window for gyro-TWT allows low heat loads in the ceramic and consequently low temperature increase.

The analysis of the lossy interaction structure for Ka-band Gyro-TWT has been carried out and discussed. In this paper, dispersion and interaction impedance characteristics of the interaction structure have been determined using 3-D simulator CST-MWS. The beam-wave interaction analysis has been carried out using particle-in-cell (PIC) code MAGIC. The simulated result shows that the interaction structure can produce more than 30 kW output power, 40 dB saturated gain, and 3dB bandwidth for Ka-band. The method of broad banding a gyro-TWT at relatively large gain by lossy loading the circular waveguide by axially periodic loaded dielectric have been presented in this paper.

One interesting method of microwave pulse compression is passive-frequency-based microwave pulse compression where a dispersive medium is used to compress a frequency swept pulse. Oversized circular waveguide having helical corrugation supports eigenmodes that are suitable for pulse compression for frequency modulated input pulse is as shown by Brat et.al. [IEEE Trans. Plasma Sci., vol. 33, no. 2, pp. 661-667, 2005.]. In this paper, theoretical studies on microwave pulse compression in helically corrugated waveguide is presented. The numerical results show a eleven fold peak power compression.

The effect of temporal pulse-shape on the characterization of the longitudinal electric field resulting from the tight-focusing of an ultrashort few-cycle TM01 laser beam in free space is investigated analytically and numerically. The longitudinal field is found to be sensitive to the pulse-shape of the driving field. The temporal pulse-shapes considered are Gaussian, Lorentzian, and hyperbolic secant having identical full width at half maximum of intensity. Analytical calculations are made beyond the paraxial and slowly varying envelope approximations. From the numerical results we find that due to finite duration of the signal, the evolution of the pulse envelope before the waist is faster (negative time-delay) but slowed down (positive time-delay) after the waist. This time-delay, for single-cycle pulses of wavelength lambda(0), and for spot-size w(0f) in the range 0.6 lambda(0) > w(0f) > 0.25 lambda(0), is pulse-shape dependent. The time delay is maximum for the Gaussian pulse and minimum for the Lorentzian pulse. The carrier frequency shift depends on the temporal profile of the pulse, beam spot size, axial propagating distance and also on the number of cycles in a pulse. In addition, a comparative study of the variation of the corrected axial Gouy-phase of the longitudinal electric field of single-cycle pulse (spot size w(0f) = 0.5 lambda(0)) with normalized retarded time shows that the phase variation is maximum for Gaussian and minimum for the Lorentzian pulse shape.

This paper presents the result of simulation studies of resonant reflector used for reflection of backward wave in relativistic BWO. The resonant reflector is modelled and analyzed by CST MWS for TM01. A TM01 mode is fed at the output end of the BWO and signal is observed at the cathode end. Results show that 90 percent of the backward TM01 wave is get reflected back by the locked TM02 mode in the resonant reflector.

A four beam electron gun has been designed for multi-beam klystron using commercially available software OPERA 3D and the optimized beam focusing has been again examined through CST particle studio. This paper represents the effect of radial position of aperture in a pole piece in focusing of multi-beam electron gun. The operating voltage of electron gun is 4 kV with total beam current of 256 (64×4) mA and beam perveance of 1.01 μP which is equally divided among all the beamlets.

In this paper investigates the design of water edge cooled single-disc CVD-diamond window for 120 GHz, 1MW gyrotron. The design of RF window for 120 GHz, 1MW gyrotron has been carried out using the CST microwave studio. In 120 GHz gyrotron single disc of diameter 90 mm and thickness 2.0 mm CVD diamond window has been used in the simulation. The return loss (S11) and transmission loss (S21) of the 120 GHz gyrotron window have been found – 40.0 dB and -0.02 dB respectively. Thermal analysis of single disc rf window has also been carried out using ANSYS software for high power 120 GHz gyrotron. The temperature range on the disc surface has been found to be 100°C–300°C.

Summary form only given. In GYRO-TWT, the RF wave propagates in the smooth wall cylindrical waveguide structure with a speed greater than the speed of a light. Such type of interactions structure used in gyro-TWTs are not capable of providing fairly wide device bandwidth due to rapid change in group velocity with frequency, at or near the cut off frequency of waveguide, which causes a narrow band coalescence between beam mode line and waveguide mode dispersion hyperbola. Wider bandwidths are achievable from this device using special type of loaded waveguides. The analysis has shown that the shape of the dispersion characteristics depends on the disc thickness, though not as much as it does on the disc-hole radius and the structure periodicity. The prediction of the effect of the structure or disc parameters on the control of the structure dispersion characteristics and their shape by the analysis ignoring the finite disc thickness more or less continues to hold good when the analysis is improvised by including the finite disc thickness. However, the improved analysis has further added to the prediction that, out of the parameters, namely, the structure periodicity, the disc-hole radius and the disc thickness, while the structure periodicity continues to be the most effective, the disc thickness proves to be the least effective, in controlling the dispersion shape, more precisely, in widening the frequency range of the straight-line portion of the dispersion characteristics. A decrease in the value of the structure periodicity has led to the widening of this frequency range. As for the disc-hole radius, it has to be optimised for maximising the frequency range of the straight-line portion of the dispersion characteristics.

A four-beam electron gun has been designed using OPerating environment for Electromagnetic Research and Analysis (OPERA) 3-D to demonstrate the dependence of beam focusing on the thickness and the radial position of anode aperture in a pole piece with reference to the gun axis. The study is important in the sense that focusing the off-axis electron beamlets are a bit difficult with a common focusing system. The OPERA simulated results have been also compared with computer simulation technique simulated results. An example of four-beam electron gun to deliver a total of 428-mA (107 x 4) current at 6-kV beam voltage has been considered for carrying out the aforementioned study. The four electron beamlets are generated through four individual cathodes, surrounded by electrically isolated four beam focusing electrode and corresponding four individual anodes and a common focusing system.

In this paper investigates the design of edge cooled single-disc CVD-diamond window for 120 GHz, 1 MW gyrotron. The design of RF window for 120 GHz, 1 MW gyrotron has been carried out using the CST microwave studio. In 120 GHz gyrotron single disc of diameter 90 mm and thickness 2.0 mm CVD diamond window has been used in the simulation. The return loss (S11) and transmission loss (S21) of the 120 GHz gyrotron window have been found -40.0 dB and -0.02 dB respectively. Thermal analysis of single disc rf window has also been carried out using ANSYS software for high power gyrotron. The temperature range on the disc surface has been found to be 50°C-150°C.