A comparison of L-band helix TWT experiments with CHRISTINE, a 1-D multifrequency helix TWT code

Extensive experimental measurements were carried out to test the accuracy o f the parametric helix traveling-wave tube (TWT) code, CHRISTINE [1], The m odel is one-dimensional, with beam electrons represented as rigid disks, Mu ltifrequency interactions are supported and the RF circuit can be optionall y represented with cold-test data, a sheath helix model, or a recently impl emented tape helix model [2], Simulations using the tape helix model are sh own to be in good agreement with experimental measurements of an L-band TWT over a broad (250-MHz) frequency range. In the intermediate and saturated power regimes, the modeled and measured TWT gain versus frequency agree to better than 0.4 dB, with deviations explained by strong reflections at the output window that are not accounted for in the code. Single-tone experimen tal and simulated drive curves agree to better than 1 dB in the small- and large-signal regimes; relative phase shift simulations agree to within expe rimental measurement accuracy in the small-signal regime and to within 75% in the large-signal regime. Two-tone experimental and modeled data exhibit similarly good agreement, with CHRISTINE accurately predicting the effect o f frequency-dependent gain variations on the TWT output response and third- and fifth-order intermodulation products.