Numerical cold testing for plasma loaded slow-wave circuits

Summary form only given, as follows. A computer model is developed which numerically calculates the electromagnetic eigenfields and dispersion relation for periodically loaded slow-wave circuits in vacuum and in the presence of a plasma. The presence of a plasma is captured by admitting a space dependent dielectric constant into the circuit. A wave equation in finite difference form is first numerically solved which produces a sequence of eigenfrequencies and eigenfields beginning with cut-off. Fourier decomposition of each eigenfield along selected mesh lines coincident with the location of the electron beam is then performed to establish a correspondence between eigenfrequency and wave number. From this data the dispersion relation for the slow-wave structure can then be formed. This numerical procedure has been demonstrated to require only a few minutes of simulation time on typical workstations. Quantities important in cold circuit testing are calculated for various waveguide structures and plasma density distributions. A vector potential formulation is compared with a numerical approach based on the direct calculation of electromagnetic fields.