MAGIC3D FDTD EM-PIC code analysis of a many-loop serpentine with partial cells

In order to compute microwave devices with greater broadband fidelity, the MAGIC3D [1] finite difference electromagnetic particle-in-cell (FDTD EM-PIC) code has been upgraded to include non-conformal or “cut” cells. The code solves Maxwell's equations in Cartesian coordinates using full rectangular and partial cells cut arbitrarily along flat surfaces. This paper describes the application of the code to a manyloop serpentine slow wave device with the goal of quantifying the importance of cut cells. Frequency dispersion analysis is performed for the structure. Time-dependent beam transport is presented showing smoother response for the cut cells, as expected (and previously observed for a 7-loop case
¹
). The Figure shows the 31-loop serpentine modeled with cut cells. Voids are cut through a solid block conductor for an electron beam tunnel, the electromagnetic (EM) wave loops, and the feedback path. Ports in the feedback path allow EM to excite the structure for the cold test. The outline of the partial cells is displayed as a dark line at the void-conductor boundaries of the otherwise conventional step cells. The cut-cell-rendered geometry is smoother yielding a less noisy, more accurate simulation. The device was excited with a 563 GHz EM pulse at the port at the right end of the feedback path. The transmitted power is modestly affected by the refined treatment for this case. The full paper will present the eigenmode cold test of the structure with dispersion, and hot test response with an electron beam in order to illustrate benefits of cut cells.