[en] Experiments on plasma formation in high-current diode cathode with magnetic insulation for production of kiloampere currents of negative hydrogen ions are described. Currents of up to 7 kA at current density up to 200 A/cm² are attained

[en] A new flowsheet of negative ion (H^-) pulse kiloampere current production in a diode with magnetic insulation, when initiating dielectric surface breakdown by laser radiation, is suggested. Experiments on H^- production were carried out using the ''Impulse'' accelerator with voltage pulse of 500-800 kV and current of 30 kA. Neodymium glass laser with pulse duration of 30 ns, laser radiation flux density of 10⁹ W/cm², was used. H^- yield equal to 10¹⁴ particles per impulse was detected. The results obtained showed the efficiency of the method suggested and its applicability for ion gun development

[en] Fine W, Mo, Al, NiCr, Au, Ag, Ti, and other wires, exploded by a 4.5 kA amplitude, 1.4 micros, have been imaged using direct (point-projection) x-ray backlighting as late as 12 micros after the start of the current pulse. The exploded wires, which ranged from 7.5 W to 13.5 microm W, Au, Al and Mo to 25 microm Ti and NiCr, were located about 6 cm away from two Mo X-pinch x-ray backlighter sources. The X-pinches are placed in parallel between the output electrodes of the 450 kA, 100 ns XP pulser at Cornell, each thereby producing a sub-nanosecond x-ray pulse. The source size is small enough to permit micron-scale spatial resolution images of the exploding wires on x-ray film. Changing the relative timing between the 4.5 kA current source and the XP pulser varied the image time. Wires were typically pulsed in pairs, reducing the peak current per wire accordingly. The behavior of the exploded wires on the microsecond time scale depends upon the material. For example, the W wires initially expand slowly (for ∼ 1 micros), and then quickly develop a fine structure in their interior. A more rapid expansion phase follows for a few micros leading to a few hundred microm diameter exploded wire by the time the current damps away. After that, the remnant wire core appears to break up into droplets. Mo and NiCr wires behave similarly. By contrast, high initial conductivity wires, such as Au and Ag, pass through a highly structured phase very quickly and form a rapidly expanding, radially symmetric vapor/plasma cloud in just a few hundred nanoseconds with a peak current of 2 kA per wire. By 2 micros after current initiation, Au wires have formed a several hundred microm diameter vapor/plasma which is reasonably axially uniform over the length of the wires except near the ends. The implications of these results to experiments on 10--20 MA pulsers and to code validation will be discussed

[en] it is shown in the work that mica crystals bent over 100 mm vadius sphere can be successfully applied in the experiments on the dense plasma diagnostics by X-ray spectral methods. High spectral and spatial resolution realized in the experiment allows one to apply these crystals in quite fine experiments, e.g. for measuring the transition extension parameters in the X-ray range and determining plasma parameters under 10²²-10²³ cm^-3 densities and 0.5-5 keV temperatures

[en] Dynamics of X-pinch in a diode of a powerful nanosecond current generator is studied both experimentally and theoretically. By means of X-ray probing with subnanosecond (temporary) and micron resolution one observed formation of a constriction prior to X-ray radiation flash with its subsequent rupture and decomposition. The radiation MHD-model enabled to describe the basic characteristics of the process including formation of mini- diode, formation of narrow neck, micro-explosion of the hot point formation of shock waves with subsequent rupture of constriction

[en] Calibrated density measurements in both the coronal plasmas and dense cores of exploding W wire and wire array Z-pinches, powered by the ∼450 kA, 100 ns XP-pulser at Cornell University, have been made using two-frame x-ray backlighting in conjunction with known thickness W step wedges. The backlighting images are made by Mo wire X-pinch radiation filtered by 12.5 microm Ti impinging upon a sandwich of films (Micrat VR, Kodak GWL, Kodak DEF) which have different sensitivities to increase the dynamic range of the method. A W step wedge filter is placed in front of the films, giving absolute line density calibration of each exposure with estimated errors ranging from 20 to 50%. Assuming x-ray absorption by the W plasma is the same as for the solid material, the authors are able to measure W areal densities from 3.2 x 10¹⁹ to 2 x 10¹⁷/cm². These can be converted to number density assuming azimuthal symmetry. For example, for an exploded 7.5 microm wire with a 15--20 microm diameter dense core and a 1 mm corona diameter, the implied W volume density ranges from 2x10¹⁸ to over 10²²/cm³. Integration of the line density gives an estimate of the fraction of the wire mass in the corona and core. For example, with 100 kA peak current in a single 7.5 microm W wire, ∼70% (>90%) of the W mass is in the corona after 53 ns (61 ns). The authors also observe that the corona has large, roughly axisymmetric axial nonuniformity both in radius and in mass density. In addition, the coronal plasma contains more of the W mass, expands faster and is more uniform when the wire is surface-cleaned by preheating. In arrays of 2--8 wires with the same 100 kA total current, detectable coronal plasma appears after 25--35 ns, and much of it is swept toward the center of the array, forming a dense channel. The portion of the initial wire mass in the coronal plasma increases with smaller wire diameter and decreases with greater wire number: 15% for 4 x 13.5 microm, 35% for 4 x 7.5 microm, and 25% for 8 x 7.5 microm, at 46--48 ns (unheated). Similar measurements are now being made with Al wires and an Al step wedge. Results will be presented

[en] The dynamics of the current-induced explosion of fine (7.5--40 microm diameter) metal wires has been studied experimentally for times up to 12 micros at 1--5 kA/wire. The main diagnostic technique is direct x-ray backlighting imaging of the exploding wires with 1 microm scale spatial resolution, obtained by using very short-time (<0.5 ns) x-ray bursts from a collapsing X-pinch. By varying the parameters of the X-pinch and the starting time of the discharge it is possible to obtain the backlighting images at different moments of time after the discharge onset. In the high-current regime (> 30 kA per wire), exploding wires typically show fast evaporation and ionization of the wire surface forming an unstable coronal plasma around a dense core. However, in the low-current regime (<5 kA per wire), studies of wire explosions reveal very different behavior for most wire materials. It has been observed that a substantial portion of the wire material is not evaporated and ionized but remains in a condensed state for a very long time. The clear structure shown in the x-ray backlighting images of 7.5--13.5 microm W wires as a function of time allows one to interpret different stages of the explosion as (1) efficient initial melting of the wire metal followed by (2) sudden volume boiling and (3) slow formation of a foam-like medium that consists of a liquid film sponge with vapor bubbles inside. If there is a vapor surrounding the wire, it is not detectable with the 2.5--4.8 keV x-ray backlighter (<10¹⁷/cm² areal density). During the foam formation, the wire remnant typically expands ten times in diameter, keeping the cylindrical form of the original wire. In the final stage (4) of the discharge (>5 micros), when the current through the wire remnant is negligible, the slow cooling of the sponge leads to a tree-like structure with gradual condensation of the remaining liquid phase material into separate drops. No typical plasma phenomena such as pinching and collapse of the plasma column are observed in these low current experiments. This behavior is typical for metals with high melting and boiling temperatures, W, Mo, NiCr and Ti, which also have relatively high resistivity, but not for Au, which vaporizes rapidly and with little structure

No abstract available

[en] A possibility of applying transparent diffraction of a lattice of W (∼1 μm period) for z pinch plasma spectroscopy is demonstrated. Explosion of 20 μm diameter thin wires of Al, Cu, Pd, W under 200 kA currents is investigated in ∼100 ns duration pulse. The distance from the source to the lattice is 318 mm, the distance from the source to the recording plame is 525 mm. Spectral resolution is ≅2.6 A. The limiting spectral resolution linked with uniquely small source dimensions is realized within the range of λ≥65 A. W lattices are less expensive and more transparent than lattices of Au

[en] Exploding wire and wire array experiments have been carried out in Z-pinch and X-pinch geometry using low current (4.5kA amplitude, 1.4 micros period damped sinusoid) and high current (up to 225 kA, 100 ns) drivers, X-ray backlighter images have been obtained using Mg, Al, Ti, Fe, Ni, NiCr, Cu, brass, Mo, Pd, Ag, Ta, W, Pt, Au, and Ni-coated Ti wires with initial diameters ranging from 7.5 microm (W) to 46 microm (Mg). There were typically two Mo X-pinch x-ray backlighters which generated pulses of <0.5 ns duration from sources small enough to allow resolution of ∼1 microm scale structure in the resulting images. In the high current experiments, images of dense cores within coronal plasmas are obtained with higher Z materials including Ni, Cu, Mo, Pd, Ta, W, Pt and Au; with lower Z materials, only the dense cores are visible in the backlighter images. In all cases a fine structure in the interior of the dense cores, and/or surface instabilities are observed. some of the dense cores show a shock-wave-like structure and others show gaps that open up more rapidly than the wire cores are expanding. The wire interiors develop a foam-like liquid-vapor mix, with some of the bubbles breaching the surface and spewing vapor out of the dense core. The low current experiments follow the same general behavior but require several μs to complete the process instead of 50--100ns. With W and Al wire explosions, step wedges have been used to permit calibrated density measurements to be made of the core (W and Al) and coronal (W) plasmas. The two X-pinches have also been used to radiograph each other, yielding high resolution images of the on-axis collapsing z-pinch and minidiode formation at the X-pinch cross point very close to the time of x-ray burst emission