Theory and computer simulation of electromagnetic wave interaction with a dynamic plasma in a cavity

The transformations of a single mode electromagnetic wave in an isotropic Lorentz plasma medium confined in an one-dimensional cavity was studied. The effect of sudden (fast) switching of the plasma was formulated by Laplace transforms. Green's perturbation technique and the Finite-Difference Time-Domain (FDTD) method was used to study the linear switching (finite rise time) of the plasma medium. The frequency upshifting and amplitude variations for both the cases are extensively presented. The linear profile for time variant and space invariant plasma derived by Green's and FDTD was compared with Airy's or Exact solution. Couple of time and space varying plasma profiles was also studied by the FDTD method. For code compactness Perfect Electric Conducting (PEC) boundaries was assumed for the FDTD method. As per the study, it is shown that the fundamental wave in the cavity experiences a frequency upshift and a perceivable decrease in amplitude for the sudden switching as well as in the linear profile case. The study also verified the existence of a dc wiggler field contribution to the EM wave when the plasma medium is switched suddenly at a switching angle of 90 degrees. The evolution of the electromagnetic wave is presented to clearly state the change in frequency and also the decrease in amplitude.