摘要:

The implosion dynamics for a neon gas‐puff z‐pinch is investigated to study the correlation between the initial and final conditions. Several nozzle material combinations are tested along with other variable parameters such as valve plenum pressure and capacitor bank voltage. The 5‐cm diameter annular nozzle consists of an inner‐core surrounded by an outer‐mantle. The pinch is driven by a 5 kJ, 30 kV, 11 &mgr;Fd capacitor bank which delivers 0.4 MA in 1.4 &mgr;s. The effects of different initial conditions on the final compression and x‐ray yield are described, based upon the following diagnostics: dIload/dt, filtered XRDs, x‐ray filtered pinhole photos, framing camera photos, and N2laser interferometer.

ISSN:0094-243X    

DOI:10.1063/1.2949183

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have conducted experiments with aluminum, copper, and gold wires arrays to study x‐ray production, z‐pmch stability, and heating mechanisms. Time‐resolved x‐ray pinhole camera data and PCD data clearly show that the maximum in the keV x‐ray production occurs after peak compression during an expansion phase.The data are consistent with a sheath whose width is determined by the number of wires of the initial array (azimuthal uniformity) and the array diameter. The final stagnated size of the pinch is set by that sheath thickness. The stagnation event is characterized by a relatively uniform initial pinch reaching, in some cases, a diameter< 1 mm, followed by a disruption and increased x‐ray production. The source of this energy is apparently not kinetic. The kinetic portion of the energy should have been converted to thermal energy near the time of maximum compression. For aluminum and copper wire arrays, heating from classical Spitzer resistivity is insufficient to explain the observed x‐ray yields. While our present data does not show the actual location of current sheath nor does it give the position of non‐radiating plasmas and, hence, is incomplete, the data when taken as a whole is strongly suggestive of enhanced resistive dissipation and an MHD instability with a helical shape.

ISSN:0094-243X    

DOI:10.1063/1.2949185

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A technique for predicting the shape of Z‐pinch implosions based on gas jet nozzle geometry has been developed and tested against data from argon gas experiments on BLACKJACK 5. The prediction technique involves use of a code which calculates the gas distribution, as a function of nozzle geometry and initial gas input pressure, at the start of the implosion. The calculated gas distribution is then snowplowed to about 0.1 of its initial radius using the measured current waveform. When the snowplow calculation is stopped, the shape of the implosion is compared to experimental data from the associated pinch.The code 2‐DRZDELTA calculates the 2‐D axisymmetric time dependent solution for the viscous compressible Navier‐Stokes equations on a triangular gridded mesh. At the time corresponding to the arrival of pulsed power at the gas jet, the density profile of the expanding argon gas is frozen. This 2‐D density profile is then used as the starting point for the 2‐D snowplow code which computes the pinch dynamics driven by J x B forces in the snowplow approximation.This technique could be used to predict implosion shapes from nozzle geometry for any driver.

ISSN:0094-243X    

DOI:10.1063/1.2949186

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A set of experiments was recently completed at the SATURN plasma radiation source (PRS) facility at Sandia National Laboratories. The purpose of the experiments was to compare the results of K‐shell yield measurements made on SATURN from aluminum wire array z‐pinch implosions to a similar set of measurements made at the Double EAGLE facility at Physics International, Inc.. These experiments were designed to study the behavior of the kilovolt x‐ray yield from aluminum z‐pinches when a tradeoff is made between the amount of mass imploded and the maximum velocity that is achieved in the implosion. A comparison of the experimental results, however, suggests that a tradeoff between the mass imploded and the implosion initial conditions may be involved in determining the K‐shell emission capabilities of these aluminum array implosions; namely, as the mass of the wires is increased, the coupling between the explosion of each single wire and the implosion of the array itself is increased. A simple wire explosion model is employed and applied to each of the SATURN and Double EAGLE experiments to make this case.

ISSN:0094-243X    

DOI:10.1063/1.2949187

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Implosions of a small neon Z‐pinch with 120‐ to 230‐kA current pulses are studied to establish neon plasma conditions appropriate for sodium‐neon photopumping experiments. Plasma compression and heating are determined from measurements of soft x‐ray, XUV, and NUV radiations from the ionization states: NeIII, NeVII, NeVIII, and NeIX. Changes in conditions of the imploded plasma with variations of the initial neon gas density and the magnitude of the driving current are described.

ISSN:0094-243X    

DOI:10.1063/1.2949190

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Here are discussed the experiments with high‐current nanosecond discharges through metal wires and dielectric fibres on NIKE‐3 device (100 kA, 50 ns) and BIN one (250 kA, 100 ns). Discharge regime is investigated as a function of load linear density &mgr; by way of example of glass fibres. While mass is increasing discharge through diode changes from regime mismatched regime with electron beam generation (&mgr; < 4 &mgr;g/cm) through hot spots forming regime (&mgr; = 8–20 &mgr;g/cm) and then to intense radiating skin‐shell regime (&mgr; > 30 &mgr;g/cm). Strong influence of surface condition on metal wires explosion character was found. The explosion of the metal wires heated up to 300–500°C for cleaning the surface was the most stable. The experimental results of the wire explosion were explained by the metal‐plasma transition model. The results of optical measurements of the plasma movement and column instability development during the discharge process are presented. In several experiments simultaneous development of kink and sausage instability was observed. 2D simulation of the sausage instability according to ideal MHD model corresponds well with experiments.

ISSN:0094-243X    

DOI:10.1063/1.2949191

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The physics of fibre making and existing devices are reviewed and a new design suggested. The yield stress of the extruded material, the extrusion pressure and the die shape are identified as important factors for successful extrusion.We propose that the fibre be extruded through a laser drilled aperture held at a temperature T1at which the H2or D2is solid. The yield stress of the solid can be varied by changing T1The aperture is connected by a capillary along which there is a temperature gradient. At the top of the capillary is a reservoir of liquid H2or D2held at a temperature T2. By varying T2and hence the saturated vapour pressure above the liquid, the extrusion pressure can be accurately controlled. Initial results are reported.

ISSN:0094-243X    

DOI:10.1063/1.2949192

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We are investigating the dependence of the fiber diameter in POW experiments on the dynamics of the implosion. Recent data from the JEX experiment at Troitsk suggest that the diameter of the fiber plays an important role in the dynamics of the implosion. In general, the smaller fiber diameter permits a more stable implosion possibly due to a higher impedance. High impedance in the fiber forces the current during the initial stages of the implosion to flow preferentially in the outer plasma shell and, thus, prevent the fiber from prematurely exploding. This suggests that there is a maximum diameter fiber that can be used to give a stable core during the compression phase of the implosion. In our experiment, an aluminum plasma jet is created from an exploding foil and then imploded onto a micron sized diameter copper wire (7–50 &mgr;m). In addition, an axial DC magnetic field (Bz0 ≤ 300 G) is applied externally to stabilize the imploding aluminum plasma and to study the interaction of the magnetic field with different diameter wires. We have found in previous experiments that the load configuration can significantly affect the magnetic field required to optimize the implosion. For example, peak x‐ray production for a load consisting of a 25 &mgr;m copper wire occurs at fields of 150 G while the aluminum jet alone is optimized at 50 G. The pinch is driven by a 2 &OHgr;, 0.1 TW generator (250 kA in 80 ns). Diagnostics include filtered PIN XRDs, time‐resolved schlieren photography, and time‐integrated multiple filtered pinholes.

ISSN:0094-243X    

DOI:10.1063/1.2949193

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An extensive programme of research, both experimental and theoretical, into the stability and dynamics of Z‐pinches has led to the funding of the DZP Project to study both radiative collapse of Z‐pinch plasmas and pinches close to thermonuclear fusion conditions. The MAGPIE (Mega‐Ampere Generator for Plasma Implosion Experiments) generator (2.4MV, 336kJ, 200ns) is now being commissioned ready for Z‐pinch experiments commencing this summer. The design of the generator has been determined by the perceived requirements demanded by consideration of (a) fusion conditions with end losses to electrodes, (b) radiative collapse at currents well above the Pease‐Braginskii limit, and (c) stability studies particularly under large ion Larmor radius conditions. As a result, and in contrast to other generators in the>1TWclass this has a long pulse length (200ns) and a final line impedance of 1.25 ohm. The stability regimes together with theoretical and experimental results are reviewed in the framework of the I4a‐N diagram. Our understanding (albeit incomplete) of other phenomena characteristic of Z‐pinches, namely the formation of electron beams, dense spots of intense X‐ray emission, ion beams and filaments will be summarised.

ISSN:0094-243X    

DOI:10.1063/1.2949194

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The construction of MAGPIE, a terawatt pulsed power facility, has been completed at Imperial College, London. The generator consists of four 2.4MV, 86kJ Marx banks each feeding a 5&OHgr; coaxial pulse forming line. The pulse forming lines are connected, via four trigatron switches, to a vertical coaxial transfer line and hence to the load. The generator is specifically designed to drive high impedance loads, enabling radiative collapse experiments to be carried out in cryogenic Hydrogen fibres. This requires the capability to deliver 1.5MA into a 100nH load in 150ns. A review of the project to date is given. This includes the design philosophy behind the generator, emphasising its unique aspects, and an outline of the tests which have been carried out to optimise its performance. Results from the first stage in the commissioning of the generator are also presented. This involved the firing of the complete generator, charged to 60&percent; of maximum voltage, into a 150nH load. Currents of approximately 700kA have been achieved with an average of 7ns first to last for the four trigatron switches.

ISSN:0094-243X    

DOI:10.1063/1.2949195

出版商:AIP    

年代:1994

数据来源: AIP