Three-dimensional particle-in-cell simulation study of a relativistic magnetron

Abstract

This work is an attempt to elucidate effects that may limit efficiency in magnetrons operated at relativistic voltages (V -500 kV). Three-dimensional particle-in-cell simulation is used to investigate the behavior of 14 and 22 cavity, cylindrical, rising-sun magnetrons. Power is extracted radially through a single iris located at the end of every other cavity. Numerical results show that in general output power and efficiency increase approximately linearly with increasing iris width (decreasing vacuum Q) until the total Q becomes too low for stable oscillation in the n-mode to be maintained. Beyond this point mode competition and/or switching occur and efficiency decreases.Results reveal that the minimum value of Q (maximum efficiency) that can be achieved prior to the onset of mode competition is significantly affected by the magnitude of the O-space-harmonic of the n-mode, a unique characteristic of rising-suns, and by the magnitude of the electron current density (space-charge effects). By minimizing these effects, up to 3.7 GW output power has been produced at an efficiency of 40%.PACS 84.40.F I .

High-order nodal discontinuous Galerkin particle-in-cell method on unstructured grids

“…For detailed dimensions of the computational domain we refer to the computational simulations in Lemke et al [25]. Fig.…”

Characterization of a 16-vane strapped magnetron oscillator by three-dimensional particle-in-cell code simulations

“…Many attempts have been made at computer 3-D PIC simulation of magnetrons [3][4][5][6][7][8]. The magnetron is intrinsically a 3-D problem.…”

Coherent Structures and Chaos Control in High-Power Microwave and Charged-Particle Beam Devices

“…The onset of the unstable oscillations in magnetrons has not been analytically described to complete satisfaction, although extensive particle-in-cell (PIC) simulations can make good predictions for the instability characteristics (see, for example, Chan, Chen and Davidson, 1993;Lemke, Genoni and Spencer, 1999). Previous analytical studies included various models utilizing linear theories.…”

“…The geometry, magnetic field B u , and potential V 0 of this example provide a rectangular approximation to a typical cylindrical L-band relativistic magnetron (see, for example, Lemke, Genoni and Spencer, 1999 Computed contours of constant potential are shown in Fig. 1.3.2.…”

“…1.3.3. As a numerical example, we have considered a system with the following parameters: K 0 =512kV , V P = 49.049 kV , 5 0 =20kG , (E x (0,y)) = 0 , K = In IL = TT cm' 1 (corresponding to L = 2.0cm), and D = 0.5cm. The geometry, magnetic field B u , and potential V 0 of this example provide a rectangular approximation to a typical cylindrical L-band relativistic magnetron (see, for example, Lemke, Genoni and Spencer, 1999). Instead of directly specifying a value of n 0 , we have chosen co p /co L = 1/3 , where a) p = {4nn 0 e 2 1m) x ' 2 is the nonrelativistic plasma frequency in the electron layer, and co t .…”