Loaded delay lines for future RF pulse compression systems

The peak power delivered by the klystrons in the NLCTA (Next Linear Collider Test Accelerator) now under construction at SLAC is enhanced by a factor of four in a SLED-II type of RF pulse compression system (pulse width compression ratio of six). To achieve the desired output pulse duration of 250 ns, a delay line constructed from a 36 m length of circular waveguide is used. Future colliders, however, will require even higher peak power and larger compression factors, which favors a more efficient binary pulse compression approach. Binary pulse compression, however, requires a line whose delay time is approximately proportional to the compression factor. To reduce the length of these lines to manageable proportions, periodically loaded delay lines are being analyzed using a generalized scattering matrix approach. One issue under study is the possibility of propagating two TE_on modes, one with a high group velocity and one with a group velocity of the order 0.05 c, for use in a single-line binary pulse compression system. Particular attention is paid to time domain pulse degradation and to Ohmic losses