The intense magnetic field generated by the 20 megaampere Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories is being used as a pressure source for material science studies. An application we have studied in great detail involves using the intense magnetic field to accelerate flyer plates (small metal disks) to very high velocities (>20 km/s) for use in shock loading experiments. We have used highly accurate velocity interferometry measurements (error ∼1%) in conjunction with one-dimensional magnetohydrodynamic (MHD) simulation to elucidate details of the flyer dynamics. One-dimensional MHD simulations are able to produce experimental results with a high degree of accuracy, thereby revealing otherwise unobtainable, but useful information about magnetically accelerated flyers on Z. Comparisons of simulation results with time-resolved measurements of velocity from a shock loading experiment involving a 925 μm aluminum flyer are presented. Results show that Joule ...

Characterization of magnetically accelerated flyer plates.

Embodiments of systems and methods for compressing plasma are described in which plasma pressures above the breaking point of solid material can be achieved by injecting a plasma into a funnel of liquid metal in which the plasma is compressed and/or heated.

Systems and methods for compressing plasma

A pulsed power generator CQ-4 was developed to characterize dynamic behaviors of materials under ramp wave loading, and to launch high velocity flyer plates for shock compression and hypervelocity impact experiments of materials and structures at Institute of Fluid Physics, China Academy of Engineering Physics. CQ-4 is composed of twenty capacitor and primary discharge switch modules with total capacitance of 32μF and rated charging voltage of 100 kV, and the storage energy is transmitted by two top and bottom parallel aluminum plates insulated by twelve layers of polyester film with total thickness of 1.2 mm. Between capacitor bank and chamber, there are 72 peaking capacitors with total capacitance of 7.2 μF and rated voltage of 120 kV in parallel, which are connected with the capacitor bank in parallel. Before the load, there is a group of seven secondary self-breaking down switches connected with the total circuit in series. The peaking capacitors and secondary switches are used to shape the discharging current waveforms. For short-circuit, the peak current of discharging can be up to 3 ∼ 4 MA and rise time varies from 470 ns to 600 ns when the charging voltages of the generator are from 75 kV to 85 kV. With CQ-4 generator, some quasi-isentropic compression experiments under ramp wave loadings are done to demonstrate the ability of CQ-4 generator. And some experiments of launching high velocity flyer plates are also done on CQ-4. The experimental results show that ramp wave loading pressure of several tens of GPa on copper and aluminum samples can be realized and the velocity of aluminum flyer plate with size of 10 mm × 6 mm × 0.35 mm can be accelerated to about 11 km/s and the velocity of aluminum flyer plate with size of 10 mm × 6 mm × 0.6 mm can be up to about 9 km/s, which show that CQ-4 is a good and versatile tool to realize ramp wave loading and shock compression for shock physics.

A 4 MA, 500 ns pulsed power generator CQ-4 for characterization of material behaviors under ramp wave loading

Ceramic materials are commonly used as protective materials for infantry soldiers and military vehicles. However, during impact, intense fragmentation of the ceramic material is observed. This fragmentation process has to be correctly numerically simulated if one wants to accurately model the dynamic behaviour of the ceramic material during impact. In this work, shockless spalling tests were performed on an alumina ceramic using the high-pulsed power generator (GEPI) equipment. These spalling tests allowed us to master the experimental strain-rate magnitude of the tensile loading applied to the specimen. The spall strength is observed to be rate dependant and the experimental configuration allowed for recovering damaged but unbroken specimen which gives further insights about the fragmentation process initiated in this ceramic material. The collected experimental data has been compared with corresponding numerical simulations conducted with the DFH (Denoual–Forquin–Hild) anisotropic damage model. This modelling approach relies on the description of the main basic micromechanisms activated at high loading rates using physical parameters related to the population of defects that produces multiple cracking in the ceramic material at high strain-rates. Very good agreement was observed between numerical simulations and experimental data in terms of free-surface velocity, size and location of the damaged zones along with crack density in these damaged zones.

http://people.3sr-grenoble.fr/users/pforquin/JMPS-Zinszner-Forquin-2015.pdf

Dynamic fragmentation of an alumina ceramic subjected to shockless spalling: An experimental and numerical study

This paper describes the configuration and operation of a seven-cavity linear transformer driver (LTD) system. This LTD system is configured to deliver ~1 MV and 125 kA into a critically damped load. A detailed transmission line model coupled to particle-in-cell simulations is used to assess the system electrical performance. The evolution of the electron power flow in negative polarity is simulated, and the impact of this flow on the operation of the system with a large-area hollow electron beam diode is examined. The simulation results are compared with available electrical measurements and with dose rate measurements where a flash X-ray pulse is produced by an annular electron beam diode. These comparisons suggest that the LTD system meets the design specifications and is a robust pulsed power architecture. Additionally, the positive polarity operation for the LTD system driving a rod-pinch diode load is modeled to further assess the utility of the LTD system

Numerical Analysis of a Pulsed Compact LTD System for Electron Beam-Driven Radiography

The Generateur Electrique de Pressions Intenses (GEPI) device was the first low-inductance high pulsed power (HPP) generator based on the strip-line design. It was initially developed for the study of the quasi-isentropic dynamic behavior of inert materials. A maximum current of 3.5 MA can be delivered with a 500-ns rise time. These electrical characteristics also allow the use of the GEPI for the projection of plane projectiles (i.e., flyer plates), with a velocity over 10 km/s having already been demonstrated. The new low-inductance pulsed power generator, the Conduite d'Elements Projetes' Adaptable par Generateur Electrique (CEPAGE) device, has been developed to combine transportability, compactness, and low-cost maintenance. This compactness relies on the use of high energy, low-inductive capacitors, and switches, permitting the storage of more energy. Its size has been optimized to house it in an existing pyrotechnic facility, for performing shock-wave experiments on high-explosive materials with high-velocity metallic flyer plates of controlled planarity. We describe the experimental and numerical work done on these two generators for high-velocity flyer-plate projection and characterization.

High-Velocity Flyer-Plate Developments on Two High-Pulsed-Power Generators Based on a Strip-Line Design (GEPI and CEPAGE)

Some compact pulsed‐current generators are described here. They allow the generation of isentropic compression loading of metals and other materials. The range of pressures achievable is 30–300 kbar for the Explosive Switch Compact Generator (ESCG). This generator consists of a RLC circuit that discharges in a strip (also called plate)‐line insulated by dielectric foils. Placed on the end of this strip‐line, some material samples can be studied under dynamical loading. Typical dimensions of the tested samples are 1 mm thick, 8mm diameter. A current of 700 kA to 1.6 MA allows some 30–300 kbar ramp pressures generated with a 500ns rise time. The switch used in the ESCG is a linear‐wave‐explosive switch. 0D circuit and MHD simulations are discussed and compared with experimental results. Diagnostics based on current‐voltage and free‐surface velocity measurements are presented. Finally, the generation of isentropic compression principles and simulations discussed above are used to analyse the potential of a n...

SYRINX Project: HPP Generators Devoted to Isentropic Compression Experiments

Summary form only given. The Advanced Pulsed Power Research Module (APPRM) was created at Sandia National Laboratory (SNL) to serve as a test bed for the development of pulsed power technologies and components that could be used in future generation high power facilities. In the present configuration the test bed is comprised of a 56 stage, 850-kJ Marx generator that charges a 5.5-Ohm water insulated Intermediate Storage Capacitor (ISC) to more than 7 MV in /spl sim/1.5 us. The switches tested were located at the output end of the ISC where they connected the output to a 5.5-Ohm CuSO/sub 4/ resistive load. Several switches have been tested on APPRM. The first switch tested was an evolved version of the Sandia designed HERMES III switch. It consists of self-breakdown (cascade) section where the discharge current flows in several parallel channels, and a trigger section where the current flows through a single spark channel. The second switch tested was a Russian/Sandia Hybrid switch. The trigger section of the Hybrid switch, designed at High Current Electronics Institute (HCEI) in Tomsk, Russia, includes six HCEI composite electrodes connected in parallel to a triggered gap via a 4-uH series isolation inductor. The discharge current in the Hybrid switch trigger section flows in several parallel channels eliminating the single channel flow as in the Sandia switch trigger section. The last switch tested is a HCEI switch design where the trigger and cascade sections are comprised of HCEI composite electrodes. The design of the switches and results of these tests will be presented as well as the analysis and comparison of results.

Tests of 6-MV triggered switches on APPRM at SNL

In order to take up some challenges in metal forming coming from the recent environmental stakes, Electromagnetic Forming and Electro-Hydraulic Forming processes have been developed at the industrial scale, using the advantages of high strain rates. Such progress has been possible in particular thanks to the emergence of strongly coupled simulation tools. In this article, some examples have been selected from some industrial applications in deep forming, postforming, embossing, and complex shapes forming. It shows how in particular, the increase in formability can bring benefits to solve customer issues in the automotive, luxury packaging, aeronautic, and particles accelerator sectors. Some simulation results are presented to explain how this highly dynamic forming occurs for each of these applications.

Examples of How Increased Formability through High Strain Rates Can Be Used in Electro-Hydraulic Forming and Electromagnetic Forming Industrial Applications

The use of magnetic fields to isentropically compress materials for equation-of-state studies has been first demonstrated on the Z machine at Sandia National Laboratories. Sharing similarities with the GEPI pulser, a compact pulser has been designed and built, focusing on isentropic compression experiments. In order to achieve high compacity and fast turn around, the design is built around a solid dielectric transmission line to couple current from eight low-inductance capacitors that are switched with ultra-low-inductance multichannel gas switches operating in dry air at atmospheric pressure. A peaking stage made of 72 capacitors enhanced by a low-inductance multichannel sharpening switch brings the fundamental rise time of the pulser down to 350 ns (10%-90%). A set of inductances in parallel with the sharpening switch as well as using various gases into this switch allow us to modify the current wave shape. The pulser delivers a peak current of 4 MA at a charge voltage of 80 kV on a short circuit. The rise time can be lengthened to around 650 ns for a current of 4.2 MA. The use of postholes convoluting in a solid dielectric insulation design makes that pulser unique, as well as its compact size, ease of use, and ease of access to the load.

G. Avrillaud

Papers

High-Velocity Flyer-Plate Developments on Two High-Pulsed-Power Generators Based on a Strip-Line Design (GEPI and CEPAGE)

SYRINX Project: HPP Generators Devoted to Isentropic Compression Experiments

Tests of 6-MV triggered switches on APPRM at SNL

Examples of How Increased Formability through High Strain Rates Can Be Used in Electro-Hydraulic Forming and Electromagnetic Forming Industrial Applications

Veloce: A Compact Pulser for Magnetically Driven Isentropic Compression Experiments