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The Sphinx machine developed at the Centre d'Etudes de Gramat is based on the 1-[micro]s linear-transformerdriver (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 M J, 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. Index Terms--Current, plasma pinch, pulse power systems, switches, transformers, X-ray production.

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 1.1 [micro]s 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. Index Terms--K-shell X-ray production, plasma radiation sources (PRSs), Z-pinches.

The Centre d'Etudes de Gramat is now studying long implosion time (about 1 [micro]s) 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 be 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-[micro]s 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. Index Terms--Rayleigh-Taylor instabilities, scaling laws, wire array, Z-pinch.

The SPHINX facility (with 1-[micro]s 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 a6t 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. Index Terms--Magnetic-field effects, plasma pinch, resistance.