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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]

The SPHINX facility (with 1-μs rise time and 5 MA) has been developed for soft X-ray production at the Centre d'Etudes de Gramat, Gramat, France. The first experiments were performed with aluminum nested wire arrays Z-pinches for K-shell production. A K-shell yield of up to 25 kJ and the full-width at half-maximum of an X-ray pulse of about 50 ns were obtained with an 800-ns implosion time and a 4-MA peak current. The specific features observed during these experiments are discussed. Inner-array dynamics highlights the fact that resistivity should not be neglected in the analysis. The effect of the return-current housing on the array dynamics, as well as the ways to mitigate it and control its impact on the radiation pulse, is also examined. [ABSTRACT FROM AUTHOR]

SPHINX is a microsecond linear transformer driver LTD, used essentially for implosion of Z-pinch loads in direct drive mode. It can deliver a 6-MA current pulse within 800 ns into a Z-pinch load. The dynamic load current multiplier concept enables the current pulse to be modified by increasing its amplitude while reducing its rise time before being delivered to the load. This compact system is made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight postholes), and a vacuum closing switch, which is the key component of the system. Several different schemes are investigated for designing a vacuum switch suitable for operating the dynamic load current multiplier on the SPHINX generator for various applications, including isentropic compression experiments and Z-pinch radiation effects studies. In particular, the design of a compact vacuum surface switch and a multichannel vacuum switch, located upstream of the load are studied. Electrostatic simulations supporting the switch designs are presented along with test bed experiments. Initial results from shots on the SPHINX driver are also presented. [ABSTRACT FROM PUBLISHER]

SPHINX is a microsecond linear transformer driver located at Atomic Energy Comission (CEA) Gramat (France), which can deliver a current pulse of 6 MA within 800 ns in a Z -pinch load. Using the concept of the dynamic load current multiplier (DLCM), which was proposed by Chuvatin, we expect to increase the load current above 6 MA, while decreasing its rise time to \sim300 ns. The DLCM developed by the CEA Gramat and International Technologies for High Pulsed Power (ITHPP) is a compact system made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight post-hole rods), and a closing switch (compact vacuum surface switch). The latter is a key component of the system, which is used to prevent the current from flowing into the load until the inductance builds up due to the implosion of the wire array. This paper presents the design and testing of the DLCM surface switch, resulting from both electrostatic simulations and experiments on the SPHINX generator. These studies, carried out either with or without load (open circuit), were valuable for a first experimental evaluation of the DLCM scheme in a microsecond regime and provided detailed information on the surface switch behavior. [ABSTRACT FROM AUTHOR]

Results of the experiments carried out on the GIT-12 generator at the current level of 3.5 MA and the Z-pinch implosion times from 700 ns to 1.1μs are reported. A gas-puff-on-wire-array (triple-shell) load configuration with the outer double gas puff (neon) and the inner wire array (aluminum) was used in the experiments. In the course of the research, implosion dynamics of the triple-shell Z-pinch was studied, and the radiation yield in the spectral range of neon and aluminum K-shell X-rays has been measured. Optimization of the inner wire array parameters (masses and initial diameters) aimed at obtaining the maximum aluminum K-shell radiation yield has been carried out. [ABSTRACT FROM AUTHOR]

The Centre d'Etudes de Gramat is now studying long implosion time (about μs) plasma radiation sources. Z-pinches are routinely used by other laboratories in the 100-ns regime with the well-known experimental result, in which an about 2-cm initial radius should not he exceeded to preserve the quality of the implosion for a single array. In a many hundreds of nanoseconds implosion time scale, the question is raised if a bigger radius could be shot. This paper discusses a theoretical approach, which shows that a 7-cm radius is acceptable in the 1-μs regime. It is based on an analysis of magneto-Rayleigh-Taylor instabilities of the accelerating sheath in the r-z plane. It will be demonstrated that all the spatial features of the implosion are determined by the magnetic skin depth, and so essentially depend on the square root of the implosion time. Experiments were carried out with SPHINX generator at the 4-MA level with 800-ns implosion time and confirmed these results. [ABSTRACT FROM AUTHOR]