A long pulse 100 microseconds Klystron-Modulator for RF power generation in the Drive Beam Linac of the CLIC Two Beam Linear Collider

This paper discusses the baseline, line-type modulator design being considered for powering the CLIC drive beam klystron RF sources. It is a conventional design but uses recent technology to improve efficiency and reliability. A high voltage pulse-forming network (PFN) charging system with several switched-mode power units in parallel enables a compact modulator layout with efficient conversion of the AC wall plug power into DC charging energy. The high power output stage consists of a simple Rayleigh, multi-cell PFN that is discharged by a thyratron switch, as a high power 100 microseconds long pulse, into the klystron load via a step-up pulse transformer. The parameters of this modulator, for a 3 TeV accelerator design, and suitable for powering an initial 25 MW, 937 MHz, multi-beam klystron are discussed. The parameter changes that will be required for using this modulator with the target design 50 MW multi-beam klystron when it becomes available are also given. The overall emphasis is to build reliability into the system at the design stage by choosing reasonable operating parameters and efficient technology, and also by keeping the design as simple as possible. Additionally, the klystron-modulator system must be easily and quickly maintainable as an important part of a very much larger accelerator complex.