摘要:

In 1995, we proposed a non-destructive type of three-stage light-gas gun having an additional preheating and filling stage which allows to regulate in a broad range the initial energy of working gas. Installation and preliminary tests of the system were almost completed. In several shots as a conventional two-stage light-gas gun with unheated helium gas, a velocity of 6.49 km/s was achieved for 1.7-g projectile. In preheating tests, a 9.5-kg pre-pump piston was reusable under the condition in which He-gas was preheated to 1080 K by compressed air of106&hthinsp;Pa.A relaxation time of heat conduction loss through the pre-pump wall was estimated to be 96 ms from the pressure profile of He-gas confined. In the case of powder, the peak temperature of He was achieved to the value of isentropic compression, 1300 K, and was in good agreement with the value estimated from the sound velocity. From simulation, we propose the concept of operational mode limits that is the difficulty to regulate pressure/temperature profiles with time in the conventional gun, and the preheating effects can suppress these mode limits. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303671

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Aluminum has been investigated at multi-Mbar pressures through planar impacts generated by guns and explosives, and ablatively driven shocks from high energy lasers. Because it is well characterized, it is often used as a reference in relative Hugoniot measurements. To determine equation of state measurement capabilities on the Sandia Z accelerator, Hugoniot states of type 1100 aluminum were determined in the 1.8 to 4.5 Mbar range for comparisons to published data. Ablatively driven shocks on 6.5 mm diameter samples were measured using velocity interferometry and laser based shock arrival sensors. In each experiment, both shock and particle velocities were independently measured to determine Hugoniot states. Many of the experiments performed had multiple measurements of these two parameters for redundancy and diagnostic validation. Results indicate agreement with the extrapolation of a previously established, lower pressure, Hugoniot within error bounds representing the experimental uncertainties. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1307305

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Recent NOVA laser experiments featuring ablatively-generated data on very small liquid deuterium samples have shown an unexpected degree of compressibility in deuterium as it undergoes molecular dissociation to a metallic phase above 25 GPa. To test these controversial results under somewhat different shock loading conditions, we have developed a cryogenic target system on the Sandia Z pulsed radiation source for precision EOS studies of liquid deuterium using radiation-driven shocks. Experiments are underway to develop a constant pressure drive of 10–20 ns duration spatially uniform over a relatively large area (3–4 mm diameter) with minimal preheat effects. Techniques are also being developed to perform fiber-optic-coupled VISAR interferometry, active shock breakout, and optical spectroscopy measurements on the stepped Al pusher plate and liquid deuterium sample in the Z bremsstrahlung environment. Initial VISAR measurements have been able to track the highly reflective metalized shock front propagating in deuterium at pressures of about 55 Gpa. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303672

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The thin foil acceleration method was tested in explosively-driven experiments with shock compressed PMMA and polyethylene at shock pressures up to 35 GPa. A transition was observed from the behavior expected for condensed matter to the gas-like response of the PMMA samples. Measurements of the PMMA unloading isentrope have been completed by modification of the equation of state in the vaporization region. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303673

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We generally use large-scale hydrocodes to study the dynamic response of targets to high-fluence pulsed radiation loads. However, for many applications where the desired solution does not require a detailed specification of pressure- or velocity-time histories, there are simple analytic approaches that can yield surprisingly accurate results. Examples include determining either the final velocity of a radiation-driven flying plate or the impulse delivered to a structural element. These methods are all based on relatively straightforward use of conservation of mass and momentum, but they typically need one scaling-law parameter. In this context, short pulse means short compared to the characteristic time of the desired response, which allows for the phenomena to be essentially uncoupled. High fluence means that the input energy is great enough to yield vaporization or blowoff of one or more portions of the configuration. We discuss some of these methods, give examples, and suggest limitations and criteria for their use. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303674

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

An experimental and analytical study of thin laser-accelerated flyer plates in a confined geometry is presented. Its objective is to improve the coupling efficiency between the flyer kinetic energy and the laser energy. Performed with a 7 &mgr;m thick aluminum flyer integrated in a three-layered target using a Nd:YAG laser (1.06 &mgr;m wavelength and a pulse duration of 8 ns FWHM), this study consists in finding the best ablating material of the first layer, responsible for the plasma generation. Flyer velocities between 2 and 5.5 km/s have been achieved for the 1–7 GW/cm2laser power density range. Best results yield coupling efficiencies of almost 50&percent;. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303675

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Experiments are being developed to shock compress metal foils in the solid state to study the material strength under high compression. The x-ray drive has been characterized and hydrodynamics experiments performed to study growth of the Rayleigh-Taylor (RT) instability in Al foils at a peak pressure of about 1.8 Mbar. Pre-imposed single mode modulations with an initial wavelength of 10–50 &mgr;m, and amplitude of 0.5 &mgr;m show growth. Variation in the growth factors may be a result of shot-shot variation in preheating of the Al sample due to emission from the plasma in the hohlraum target. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1307306

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A laser-launched miniature flyer system (MiniFlyer) is being used to study the dynamic properties of materials. A 3-mm diameter and 0.05-mm thick flyer plate is accelerated by a laser-pulse-induced plasma contained between a clear window substrate and the flyer plate. The substrate is coated with carbon, aluminum oxide, and aluminum to enhance the plasma formation process. The flyer impacts a gold target plate of 0.10 or 0.26 mm thickness, producing a shock. The shock pulse interacts with the free surface and reflects as a rarefaction wave, producing tension in the foil. Dynamic measurements of the free surface particle velocity were made using VISAR (Velocity Interferometer System for Any Reflector). Cross-sections of the gold targets exhibit spall planes at the expected locations. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303676

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Experimental techniques for laser-driven flyer generation offer considerable promise as a compact, repeatable, and relatively inexpensive driver for fundamental shock compression studies. Acceleration of microgram samples of thin metal films to high velocities (>3 km-s−1) using Q-switched, solid-state lasers has become well established. Scaling of these methods to provide well-conditioned shock loading with considerably larger sample dimensions and mass would greatly enhance the utility of this driver. As flyer target thickness and mass increase, however, the dynamic shear strength and yielding behavior of the material become important factors in limiting performance. Experiments exploring methods for optimizing the bounding material at the driving laser spot perimeter are described. Results are being incorporated in a 2-D hydrocode model of flyer generation to aid in optimization of target designs. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303677

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present a novel application of the spall technique for measuring the strength of metallic coatings including the adhesive strength on a metal substrate. We have utilized the capability of the pulsed high-power proton beam of the Karlsruhe Light Ion Facility to generate short, intense pressure pulses. Due to the bell-shaped beam power profile, spall fracture inside the samples occurred at different distances from the surface, including the interface between coating and substrate. Using a line-imaging laser-Doppler velocimeter, we were able to measure the free surface velocity histories for a whole range of load parameters in each single experiment. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303678

出版商:AIP    

年代:1900

数据来源: AIP