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Repetitive high-voltage square pulses are of great importance for producing long-pulse electron beams and high-power microwaves. One of possible technologies for the generation of such pulses is a Marx generator using pulse forming network (PFN) stages, often combined with a pulse sharpening technique to reduce the rise time to a few nanoseconds (peaking stage). This paper presents an innovative design, named the “zigzag design,” for the optimization of the compactness and of the rise time of 400-kV–85-ns PFN-Marx. Thanks to this design, the 16 stages of this generator, which delivers an open circuit output voltage of 720 kV, fit in a 650-mm length. For a slightly overmatched load ($Z_{\mathrm {load}} = 100 ~\Omega$), the output voltage reaches 400 kV with a rise time as less as 5 ns. The inductance reduction associated with the innovative zigzag design, which allows this sharp rise time with no need for a peaking stage, is described. The 85-ns plateau duration of the pulse is given by the PFN construction of each stage, which is based on six ceramic capacitors (2.1 nF–45 kV) connected within a strip line. The 16 PFN stages are housed in a 360-mm diameter gas pressurized vessel. Burst mode operation for a duration of 10 s at a pulse repetition frequency of 100 Hz is reported, for a resistive load and for the electron beam diode of a X-band relativistic backward-wave oscillator (BWO). To reach further compactness, the BWO system is integrated on side of the generator vessel and a U-shaped gas pressurized line connects both systems through a compact conical vacuum insulator. [ABSTRACT FROM AUTHOR]

The Sphinx machine developed at the Centre d'Etudes de Gramat is based on the 1-μs linear-transformer-driver (LTD) technology. Before 2006, it operated with 16 branches of eight LTD stages each and was used for implosion of Z-pinch loads in direct drive mode. At a charging voltage of 50 kV, the stored energy was 1.3 MJ, and the good reliability of the machine allowed many experiments on 4-MA 700-ns implosion of nested wire arrays. Parallel to these experiments, improvements on LTD stages have been achieved on test beds up to 70-kV charging voltage, leading to a new design of LTD stage, named LTD-05. The Sphinx machine has been upgraded with 144 such LTD-05 stages. Details are given on stage design, on electrical and electrostatic simulations, and on experimental results. The following subsystems modifications or developments are also described: 1) premagnetizing and triggering systems and 2) prepulse current generator for wire-array preheating. Moreover, a status on improved performances and reliability of the complete Sphinx system is given. [ABSTRACT FROM AUTHOR]