- . - 8 - a . A High - Power SLED II Pulse Compression System ”

INTRODUCTION The enhancement of peak power by means of RF pulse compression has found important application for driving high energy electron linacs, the SLAC linac in particular. The SLAC Energy Doubler [l] (SLED), however, yields a pulse shape in the form of a decaying exponential which lim its the applicability of the method. Two methods of improving this situation have been suggested: binary pulse compression [21 (BPC), in which the pulse is compmssed by successive factors of two, and SLED II [3,4] in which the pair of resonant cavities of SLED are replaced by long resonant delay lines (typically waveguides). Intermediate schemes in which the cavity pair is replaced by sequences of coupled cavities (which may be thought of as forming slow wave structure delay lines) have also been considered [5,61. In this paper we describe our efforts towards the design and construction of high-power SLED II systems, which are intended to provide drivers for various advanced accelerator test facilities and, potentially for the Next Linear Collider itself. The design path we have chosen requires the development of-a number of m icrowave components in overmoded waveguide, and the bulk of this paper will ,be devoted to reporting our progress. Success achieved with the BPC, which is currently acting as driver for testing experimental accelerator sections, has demonstrated the suitability of overmoded circular waveguide operating in the TEol mode for use as delay lines. A low-power version of SLED II has been constructed which makes use of the same waveguide. Experiments carried out with this low-power version have confirmed the high-quality output wave form predicted by the theory [7]. Accordingly it has been decided to -employ such waveguides in the SLED II system as well. This decision has driven the rest of the design. A schematic drawing of the proposed layout is shown in Figure 1. The system is being designed for high vacuum. The first realization (Prototype 1, hence Pl) will make use of-the same waveguide as that used for the BPC (WC2811 with an inner diameter of 2.81 inches. The second (P2) will use a waveguide with a diameter of 4.75 inches (WC475) to reduce waveguide loss and hence enhance efficiency. The same circular waveguide mode will be used in all SLED II components. The components required can be seen by m&e&e fo Figure 1. A mode converter is needed to convert the rectangular TElo mode from the klystron to the circular TEo, mode. This feeds into the