Analyses of Klystron Modulator Approaches for NLC

Abstract

Major changes to the Next Linear Collider (NLC) design were facilitated by the experimental testing of the 75 MW X-band klystron at a 3.0 {micro}sec pulse width and new component development allowing the delay line distribution system (DLDS) to operate with eight bins instead of four. This change has a direct effect on the design of the klystron modulator. The general approaches, which are being studied intensively, are: the conventional base line modulator with two klystrons, a Hybrid version of the baseline with a solid-state on/off switch, a solid-state induction type modulator that drives eight klystrons, and a solid-state direct switch modulator. Some form of pulse transformer is the matching element between the klystron beam and the energy store in the all of these approaches except the direct switch. The volume and cost of the transformer is proportional to the peak pulse power and the output pulse width. The recent change in the NLC design requires double the transformer effective core area, and increase both the size and cost of modulator. In the direct switch model there is no pulse transformer. The klystron beam potential is practically equal to the potential of the energy storage element. Here the solid-state switch blocks the 500 kV DC voltage of the storage element. In this paper transformerless modulator approaches are presented based upon a Marx method of voltage multiplication using on/off Insulated Gate Bipolar Transistors (IGBT's) instead of on switches. DC voltage power supply system is much simpler as compared to the power system of the direct switch approach.