Self-consistent Nonlinear Analysis Research Articles

Design and Stability Studies of Second-Harmonic Gyro-TWT Amplifier Using Wedge-Shaped Lossy Ceramic Rod-Loaded Mode Selective RF Interaction Circuit

In this paper, the design and stability analysis of a W-band second-harmonic Gyrotron Travelling Wave Tube (gyro-TWT) amplifier loaded with the wedge-shaped lossy ceramic rods, operating in the circular azimuthally symmetric TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode, has been presented. The stability of the gyroTWT has been investigated against the spurious oscillations, including the reflective oscillation, gyrotron backward oscillation (gyro-BWO), and absolute instability. The transmission loss for the operating mode has been calculated as ~19 dB/cm at 91.4 GHz for achieving the stability. Furthermore, the gyro-TWT using the distributed loaded RF section has been investigated for its nonlinear behavior using a self-consistent nonlinear analysis. The saturated RF output power of ~450 kW at 91.4 GHz with ~18% efficiency, ~30-dB saturated gain, and 3-dB bandwidth of ~3% has been achieved for an electron beam of 100 kV and 25 A.

Gyro-TWT Using a Metal PBG Waveguide as Its RF Circuit—Part I: Analysis and Design

A gyro-TWT using a metal photonic bandgap (PBG) waveguide as its RF circuit has been analyzed using a self-consistent nonlinear analysis. The analysis focuses on single-mode operation of gyro-TWT by eliminating the mode competition problem existing in an overmoded structure using a mode-selective PBG circuit. A Ka-band, TE01 waveguide mode PBG gyro-TWT has been designed, and analytical results have been computed to demonstrate the beam–wave interaction mechanism of the device. The nonlinear analysis predicted $\sim 91$ -kW RF output power with an electronic efficiency of $\sim 13$ % and the saturated gain of $\sim 40$ dB from this device.

Self-consistent Nonlinear Analysis and 3D Particle-In-Cell Simulation of a W-band Gyro-TWT

The self-consistent nonlinear analysis and CST 3D particle-in-cell (PIC) simulation of a W-band gyrotron traveling wave tube (gyro-TWT) are presented in this paper. Both the simulation results of the two codes are excellent agreement with each other. The gyro-TWT loaded with periodic lossy dielectric in the circuit for suppressing potential spurious oscillations. It is driven by a 70kV, 10A gyrating electron beam with velocity ratio of 1.0. PIC simulation results are: the maximum peak output power of 198kW, statured gain of 62.3dB and efficiency of 28.3% at 92.5GHz. Only the operating mode TE01 is observed in the CST 3D simulation and the potential competing backward wave oscillations are effectively suppressed. The CST simulation also predicts that the device works stably under the condition of the beam current lower than 14A and B0/Bg lower than 1.05. The simulated bandwidth with peak power greater than 100kW is 6.8GHz without axial velocity spread, and 4.1GHz with 6% axial velocity spread.

Analysis and PIC simulation of a Gyrotron travelling wave tube amplifier

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.

Self-consistent nonlinear analysis of a frequency-quadrupling terahertz gyroklystron

This paper analyses a three-cavity frequency-quadrupling terahertz gyroklystron with successive frequency-doubling in each cavity with self-consistent nonlinear theory. The beam–wave interaction efficiency and the electron bunching process are studied. The variation of output efficiency with the length of drift tubes and output power and the variation of Ohmic loss with the length of output cavity are considered. Numerical simulations predict an optimal output efficiency of 1.8%, a power output of more than 2 kW and a gain of 33 dB after taking into account Ohmic losses when the frequency-quadrupling gyroklystron, driven by a 40-kV, 3-A electron beam and 1 Watt input power, operates at 225 GHz.

Third-harmonic complex cavity gyrotron self-consistent nonlinear analysis

Starting from general transmission line equations with an electron beam source, a self-consistent nonlinear theoretical model for a complex cavity gyrotron with gradual transitions is presented in this paper. The model accounts for mode coupling in the transition region of the complex cavity. The interaction between the electron beam and H/sub 61/-H/sub 62/ RF field in the complex cavity for a third-harmonic gyrotron is simulated; many calculations are carried out under different cavity dimensions and electron beam parameters.

A 30-MW Gyroklystron-Amplifier Design for High-Energy Linear Accelerators

Microwave tubes required to drive future 1-TeV linear colliders have challenging requirements, including 300-MW peak power at wavelengths near 3 cm. It is believed that gyrotrons have good potential for development into the high peak power, high gain, efficient amplifier required for this application. Presented here is the detailed design for a 3-cm gyroklystron amplifier at a peak power level of ~ 30 MW. This power level is approximately three orders of magnitude above the gyroklystron state of the art, and a 30-MW experimental study will be a crucial step toward achieving the 300-MW goal. Novel problems associated with a high-energy (γ ~ 2) gyrotron beam are considered in detail. A new partially self-consistent nonlinear analysis is described and subsequently used to design the gyroklystron circuit. Based on the TE011 mode in cavities of circular cross section, stable operation is anticipated; the current is well below the threshold at which an unbunched electron beam would excite oscillations in the cavities and the drift spaces are designed to heavily load modes which are not cut off.

Self-consistent nonlinear analysis of overmoded gyrotron oscillators

The self-consistent nonlinear analysis is presented for an overmoded gyrotron, in which the gyrotropic beam interacts with more than one cavity eigenmodes. The nonlinear equations are obtained in the slow time scale for the motion of each individual particle and for the evolution of the amplitude and frequency of each individual cavity eigenmode. A numerically efficient algebraic longtime-step algorithm is developed, which includes magnetostatic field tapering and time transients. Numerical examples are presented for the excitation and competition of the cavity eigenmodes.

Computation of Ion-acoustic Wave Excitation and its Anomalous Effects for Double-sided Laser-plasma Interaction

Computer results based on a self-consistent nonlinear analysis are given for the (one-dimensional) problem of laser interaction with a plasma layer. Effects of ion-acoustic wave excitation are studied assuming that the plasma is exposed to incident radiation from two oppositely directed laser beams.

One-dimensional Model for Nonlinear Reflection of Laser Radiation by an Inhomogeneous Plasma Layer

A self-consistent nonlinear analysis is given for the (one-dimensional) problem of laser interaction with a plasma layer. The main process considered is the decay of the laser wave into an ion sound wave and a reflected wave. Nonlinear reflection is shown to be possible even for a linearly transparent layer. The reflection and absorption coefficients are studied as functions of as a function of the level of excitation of the ion sound waves in the plasma. The range of parameters for which the reflection or the heating is maximum is considered.