An examination of the performance of backward wave CFA's in simulation and experiment

This paper presents comparisons of 3D simulations of amplitrons (backward wave CFAs) under cold test (no electrons present) with experimental cold tests. These include measurements using both S/sub 11/ and S/sub 22/ parameters vs. frequency methods. Results both for the so-called "baby" amplitron, an S-band tube currently used by the Navy, and a new experimental ultra-high-average-power UHF amplitron are presented. The baby is of interest in that it exhibits spurious output, ostensibly due to resonant phenomena caused by impedance mismatches within the tube. In order to study this in detail, MRC is performing both computer and experimental cold tests of each major section of these tubes, which includes a double ridged waveguide taper and a two-conductor TEM transmission line on both the input and the output, and the amplitron slow-wave circuit itself. Related work reported includes MAGIC hot runs on both tubes, attempting to verify performance results against experimental runs and to study spurious behavior, and MAGIC studies of multipactor.