A phenomenological model of wire array Z-pinch implosions, based on the analysis of experimental data obtained on the mega-ampere generator for plasma implosion experiments (MAGPIE) generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)], is described. The data show that during the first ∼80% of the implosion the wire cores remain stationary in their initial positions, while the coronal plasma is continuously jetting from the wire cores to the array axis. This phase ends by the formation of gaps in the wire cores, which occurs due to the nonuniformity of the ablation rate along the wires. The final phase of the implosion starting at this time occurs as a rapid snowplow-like implosion of the radially distributed precursor plasma, previously injected in the interior of the array. The density distribution of the precursor plasma, being peaked on the array axis, could be a key factor providing stability of the wire array implosions operating in the regime of discrete wires. The modified “initial” conditions for simulations of wire array Z-pinch implosions with one-dimension (1D) and two-dimensions (2D) in the r–z plane, radiation-magnetohydrodynamic (MHD) codes, and a possible scaling to a larger drive current are discussed.
A small plasma focus (3.3 kJ) is designed from the viewpoint of simplicity, reliability, and cost effectiveness to act as a source of pulsed high-density plasmas. The simplicity of the device and associated diagnostics coupled with its rich variety of plasma phenomena makes this device ideal for the teaching of plasma nuclear fusion particularly for developing countries where such facilities are at present rarely available. Six sets of the device have been constructed and tested in various gases with better than 95% reliability and reproducibility in various plasma phenomena including neutron production of 0.5–1.0×108 per discharge when operated in 3-Torr deuterium. The design principles, procedures, and parameters are discussed and test results shown.
In this paper the influence of the prepulse current on a capillary-discharge 46.9 nm Ne-like Ar extremeultraviolet laser is reported. A current pulse with a typical RC shape ͑decay time of ϳ30 s͒ was used as a prepulse. Measurements indicate that when the filling pressure is low, the output can be improved by reducing the time delay between the application of the prepulse current and the onset of the main discharge current. For high pressure the reverse is true. This change is most significant for time delays between 2 and 4 s, and beyond these time delays, the effect is less significant. This effect is attributed to the changes in the capillary channel pressure and also to the absorption of the laser emission by the plasma plume ejected during the prepulse. Thus, apart from ensuring a minimal amount of prepulse current to prevent nonuniformity effects, the timing of the application of the prepulse current is also important.The short wavelength and high peak power of amplified spontaneous emission sources in the extreme-ultraviolet ͑EUV͒ and soft x-ray regimes make them very attractive for many applications in science and technology, and they have been extensively explored in past decades ͓1,2͔. Of particular interest and importance is the development of compact, higher efficiency and low cost systems that are more affordable and accessible to make their use more widespread in important applications. The first observation of large amplification in the transitions of Ne-like ions in capillarydischarge plasma ͓3͔ and the subsequent demonstration of the saturated operation of the tabletop amplifier ͓4͔ opened up such a possibility and has attracted much attention since. In this capillary-discharge scheme, an elongated plasma column with high aspect ratio ͑ϳ1000: 1͒ is created by a fast current pulse injected into a low pressure ͑ϳ1 mbar͒ argonfilled capillary channel. The magnetic force induced by the current together with the high kinetic pressure gradients near the capillary wall compress the plasma, creating a shock wave. This compressional discharge leads to the formation of a hot and highly ionized plasma column 100-200 m in diameter. A few nanoseconds before stagnation, when the first compression shock wave reaches the axis, the plasma attains a temperature ͑Ϸ60-80 eV͒ and mean electron density ͑Ϸ5 ϫ 10 18 cm −3 ͒ necessary for lasing ͓5,6͔. This condition creates a high abundance of Ne-like argon ions in the plasma, and population inversion between the 3p 1 S 0 and 3s 1 P 1 levels is achieved through collisional electron impact excitation of the ground state Ne-like argon ions, resulting in a gain at 46.9 nm wavelength. An important criterion for soft x-ray amplification in a discharge created plasma is the existence of a stable plasma column with good axial uniformity. Axial inhomogeneities usually accompany high power electrical discharges as a result of nonuniform initial conditions and slow compression ͓7͔. To circumvent this plasma uniformity problem, the capillary channel is filled with a certain amount...
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