X-ray imaging and 3D reconstruction of in-flight exploding foil initiator flyers
Abstract not provided
Willey, T. M.↗
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Comparisons of CTH Simulations with Measured Wave Profiles for Simple Flyer Plate Experiments
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Shock Physics, Hydrocodes, Simulation↗
On the scaling of magnetically accelerated flyer plate technique to currents greater than 20 MA.
Abstract not provided.
Lemke, Raymond W↗
Laser-driven flyer plates for shock compression science: Launch and target impact probed by photon Doppler velocimetry
We investigated the launch and target impact of laser-driven Al flyer plates using photon Doppler velocimetry (PDV). We studied different flyer designs launched by laser pulses of different energies, pulse durations and beam diameters, that produced km s{sup −1} impacts with transparent target materials. Laser-launching Al flyers 25–100 μm thick cemented to glass substrates is usually thought to involve laser vaporization of a portion of the flyer, which creates many difficulties associated with loss of integrity and heating of the flyer material. However, in the system used here, the launch mechanism was surprising and unexpected: it involved optical damage at the glass/cement/flyer interface, with very little laser light reaching the flyer itself. In fact the flyers launched in this manner behaved almost identically to multilayer flyers that were optically shielded from the laser pulses and insulated from heat generated by the pulses. Launching flyers with nanosecond laser pulses creates undesirable reverberating shocks in the flyer. In some cases, with 10 ns launch pulses, the thickest flyers were observed to lose integrity. But with stretched 20 ns pulses, we showed that the reverberations damped out prior to impact with targets, and that the flyers maintained their integrity during flight. Flyer impacts with salt, glass, fused silica, and acrylic polymer were studied by PDV, and the durations of fully supported shocks in those media were determined, and could be varied from 5 to 23 ns.
36 MATERIALS SCIENCE↗
Light Initiated High Explosive Driven Flyer Plate Impulse Generation Technique For Material and Structural Response
The objective for this research has been to develop a method to induce a high frequency, large amplitude shock pulse into materials and structures as an above-ground laboratory simulation of an exo-atmospheric cold x-ray induced blow-off event. This work builds on the successes of direct-spray Light Initiated High Explosive impulse delivery technique, in order to drive a flyer to a desired impact velocity to induce the proper combined material and structural response of the target. The reported development focuses on flyer velocity from explosive initiation to target impact to flyer rebound. A comprehensive derivation of an analytical model to predict flyer velocity as a function of explosive deposition and flyer properties is presented. One-and two-dimensional test series were conducted to evaluate impulse delivery and impact pressure, as well as target material and structural response. Experimental results show good agreement in flyer velocity between that predicted by the developed theory and that inferred by impulse delivery. A definitive material response was measured in each of the one-dimensional targets. The structural strain response measured in the ring experiments showed excellent agreement with both the predicted flyer performance and the analytical strain solution for a cosine distributed impulsive loading. This work has focused on the utilization of analytical, hydrocode, and test analysis to confirm that a LIHE driven flyer impulse technique can be an effective simulation of a cold x-ray blow-off event. It is shown that a thin metallic flyer plate can be explosively accelerated to impact a target with sufficient energy to generate an impulsive load which induces both structural and material response in a test item.
36 MATERIALS SCIENCE↗
Plasma-accelerated flyer-plates for equation of state studies
We report on a new technique to accelerate flyer-plates to high velocities ({approx}5 km/s). In this work, a strong shock is created through direct laser ablation of a thin polyimide foil. Subsequent shock breakout of that foil results in the generation of a plasma characterized by a smoothly increasing density gradient and a strong forward momentum. Stagnation of this plasma onto an aluminum foil and the resultant momentum transfer accelerates a thin aluminum flyer-plate. The aluminum flyer-plate is then accelerated to a peak velocity of {approx}5 km/s before impact with a transparent lithium fluoride (LiF) window. Simulations of the stagnating plasma ramp compression and wave reverberations within the flyer-plate suggest that the temperature at the flyer-plate impact surface is elevated by less than 50 Degree-Sign C. Optical velocimetry is used to measure the flyer-plate velocity and impact conditions enabling the shocked refractive index of LiF to be determined. The results presented here are in agreement with conventional flyer-plate measurements validating the use of plasma-accelerated flyer-plates for equation of state and impact studies.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
High-speed laser-launched flyer impacts studied with ultrafast photography and velocimetry
Pulsed lasers can launch thin metal foils at km s -1 , but for precision measurements in shock compression science and shock wave spectroscopy, where one-dimensional shock compression is vital, flyer plate impacts with targets must have a high degree of flatness and minimal tilt, and the flyer speeds and impact times at the target must be highly reproducible. We have developed an apparatus that combines ultrafast stroboscopic optical microscopy with photon Doppler velocimetry to study impacts of laser-launched Al and Cu flyer plates with flat, transparent glass targets. The flyer plates were 0.5 mm in diameter, and ranged from 12-100 μm thick, with flyer speeds up to 6.25 km s -1 . The velocity variations over 30-60 launches from the same flyer plate optic can be as low as 0.6%, and the impact time variations can be as low as 0.8 ns. Stroboscopic image streams (reconstructed movies) show uniform, flat impacts with a glass target. As a result, these stroboscopic images can be used to estimate the tilt in the flyer-target impact to be <1mrad.
36 MATERIALS SCIENCE↗
Laser-driven flyer plate impact: Computational studies guided by experiments
We present a computational approach using a multimaterial, arbitrary Lagrangian–Eulerian code termed ALE3D to model the nanosecond/micrometer dynamics of the launch of 0.5–4.5 km/s laser-driven metal flyer plates and the impact with stationary targets of Pyrex and fused silica glasses, and Lexan and Plexiglas polymers, producing pressures in the target in the range of 5–20 GPa. The simulations are compared to experimental results where the flyer velocity profile and the velocity profile imparted to the target material were measured with high-speed velocimetry. The experimental flyer launch by a high-intensity pulsed laser is modeled by depositing heat into a thin vaporizable layer under the flyer plate. This model produces a flyer plate that has not been exposed to the laser pulse, allowing us to compare the properties of the real flyer to a simulated ideal flyer. The simulations of target impact are generally in good agreement with the experiment except at the highest impact velocities where the shock release process in the experiment is slower than that in the simulation. The cause of this disagreement is attributed to an inadequate description of the shock viscosity during the nanosecond unloading process.
Stekovic, Svjetlana (ORCID:0000000163878070)↗
Simplified laser-driven flyer plates for shock compression science
We describe a simplified system of laser-driven flyer plates for shock compression science and shock spectroscopy. We used commercially available one-box Nd:YAG lasers and beam homogenization solutions to create two launch systems, one based on a smaller (400 mJ) YAG laser and an inexpensive diffusive optic, and one based on a larger (2500 mJ) laser and a diffractive beam homogenizer. The flyer launch, flight, and impact processes were characterized by an 8 GHz fiberoptic photon Doppler velocimeter. We investigated effects of different substrates, adhesives, absorbers, ablative layers, and punching out disks from continuous foils versus fabricating individual foil disks, and found that a simple metal foil epoxied to a glass window was satisfactory in almost all cases. Our simplified system launched flyer plates with velocities up to 4.5 km s{sup -1} and kinetic energies up to 250 mJ that can drive sustained steady shocks for up to 25 ns. The factor that limits these velocities and energies is the laser fluence that can be transmitted through the glass substrate to the flyer surface without optical damage. Methods to increase this transmission are discussed. Reproducible flyer launches were demonstrated with velocity variations of 0.06% and impact time variations of 1 ns. The usefulness of this flyer plate system is demonstrated by Hugoniot equation of state measurements of a polymer film, emission spectroscopy of a dye embedded in the polymer, and impact initiation and emission spectroscopy of a reactive material consisting of nanoscopic fuel and oxidizer particles.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Hypervelocity launching of flyers at the SG-III prototype laser facility
Experiments of laser-driven hypervelocity flyers have been conducted at the SG-III prototype laser facility. Using the continuum phase plate technique, four laser beams each with a 3-ns quadratic profile are configured to produce relatively uniform irradiated spots of diameter size either 500 μm or 2000 μm. With the former, specifically designed multi-layered flyers (polyimide/copper) were accelerated by shock impedance and reverberation techniques via direct laser ablation to a super-high averaged velocity of 55 km/s, much faster than recently reported results. Light-emission signals of shock breakout and flyer impact on flat or stepped windows were obtained that indicated good planarity and integrity for the flyer. In the latter, single-layered aluminum flyers were gradually accelerated to a terminal velocity of 11 km/s, as measured by optical velocimetry, without melting and vaporization. The results suggest that the SG-III prototype laser facility has the capability to launch high-speed flyers to create extreme conditions for investigating the science of shock compression and its equation of state.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Evaluation of RMI Ejecta Sourcing from Reconstructed Interfaces in 2D FLAG Flyer-Plate Simulations
This study investigates the performance of RMI ejecta sourcing from a reconstructed interface in two-dimensional FLAG ejecta flyer-plate simulations. Enabling the RMI ejecta model to operate on reconstructed interfaces has been a longstanding challenge in FLAG, limiting its applicability to experiments in which interface reconstruction is not required. Addressing this limitation is therefore an important step toward expanding the model’s predictive capability. The first phase of this effort focused on identifying a flyer-plate/target configuration that produces large ejecta clouds from two distinct shocks using the standard RMI ejecta model. A series of simulations examined the effects of flyer composition, layer thickness, and mesh resolution on shock structure and ejecta formation. VISAR traces were used to evaluate shock timing and identify configurations that produced a clear double-shock response. A copper middle-layer flyer with a doubled tin layer yielded the most favorable shock characteristics and was selected as the baseline configuration. After confirming this configuration performed as expected when running a reference FLAG version, it became the basis for three simulations: (1) a standard two-dimensional ejecta flyer-plate calculation using a reference FLAG version, (2) the same calculation with the reconstructed interface option enabled, and (3) a calculation employing ALE strategies to force the ejecta model to operate on the reconstructed interface. While the baseline simulation produced the expected ejecta response, the reconstructed interface approach did not result in measurable ejecta, indicating that this capability remains under development. These results highlight both the progress made and the remaining challenges in extending the RMI ejecta model to reconstructed interfaces.
36 MATERIALS SCIENCE↗
High strain rate metalworking with vaporizing foil actuator: Control of flyer velocity by varying input energy and foil thickness
Electrically driven rapid vaporization of thin metallic foils can generate a high pressure which can be used to launch flyers at high velocities. Recently, vaporizing foil actuators have been applied toward a variety of impulse-based metal working operations. In order to exercise control over this useful tool, it is imperative that an understanding of the effect of characteristics of the foil actuator on its ability for mechanical impulse generation is developed. Here, foil actuators made out of 0.0508 mm, 0.0762 mm, and 0.127 mm thick AA1145 were used for launching AA2024-T3 sheets of thickness 0.508 mm toward a photonic Doppler velocimeter probe. Launch velocities ranging between 300 m/s and 1100 m/s were observed. In situ measurement of velocity, current, and voltage assisted in understanding the effect of burst current density and deposited electrical energy on average pressure and velocity with foil actuators of various thicknesses. For the pulse generator, geometry, and flyer used here, the 0.0762 mm thick foil was found to be optimal for launching flyers to high velocities over short distances. Experimenting with annealed foil actuators resulted in no change in the temporal evolution of flyer velocity as compared to foil actuators of full hard temper. A physics-based analytical model was developed and found to have reasonable agreement with experiment.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Computational Design of a Simple Flyer Plate Launcher
The response of materials to shock loading is important to understand for a variety of applications. When shock physics emerged during and after WWII, direct explosive loading or explosively driven plate impact was the primary tool for these studies. Subsequent decades have seen the widespread use of large caliber guns for plate impact studies, laser-shock facilities and pulsed power facilities. INL currently lacks a gun suitable for plate impact or explosives casting and machining facilities; however, it does possess explosives use and handling capabilities. An option for performing plate impact experiments was needed, therefore continuum scale models were utilized to explore a few simple donor-acceptor explosive plane wave lens designs, one of which could be hand packed with plastic explosives to launch flyer plates. 2D simulations were performed to study different geometries in an effort to minimize the difference in shock arrival across the central portion of a small copper flyer plate. A shock wave arrival time difference under 50 ns across 50 percent of the center of the flyer was achieved with a few designs. This work summarizes the computational models and results.
36 MATERIALS SCIENCE↗
Pressure Response Optimization of an Eddy Current-Driven Flyer Plate Valve for the ITER Shattered Pellet Injection System
One technique for mitigating disruptions in a tokamak is shattered pellet injection (SPI). SPI is a process in which a large solid pellet consisting of deuterium, neon, or argon is desublimated in a pipe gun barsrel and launched downstream. Pellets are shattered just before entering the plasma by an impact with an angled tube. Injection of these materials into the plasma radiates stored thermal energy, limits current decay rates, suppresses the generation of runaway electrons, and dissipates runaway electrons if necessary. A critical element of the SPI system is a fast-acting valve that releases high-pressure gas to dislodge and accelerate pellets directly, or indirectly via a mechanical punch. A prototype valve sized for the ITER SPI system has been designed and fabricated. A pulsed high-voltage power supply energizes the valve’s internal magnetic coil, which induces eddy currents in the adjacent flyer plate resulting in a repulsive force between the flyer plate and the coil. The flyer plate action lifts a valve seat, allowing high-pressure gas to flow from the valve plenum to the downstream (breech) location of the pellet or mechanical punch. All of the valve’s internal components are designed to operate in ITER-level static background magnetic fields. Here, a study was conducted to optimize the downstream pressure response for a range of valve sizes and operating pressures. In particular, the study analyzes the breech pressure response associated with varying plenum pressures as well as varying breech volumes. A computational fluid dynamics simulation was built in STAR-CCM+ and validated against data from laboratory experiments. The resulting simulation outputs, in the form of downstream responses for a variety of initial plenum pressures and breech volumes, will be used as a complement to experimental data to ensure the pressure pulse is suitable for pellet survivability. These data, combined with studies on pellet shear strength and shock response, will be applied to optimization of overall operating parameters of the ITER SPI system.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Studies of Laser-Driven Flyer Acceleration Using Optical Fiber Coupling [Book Chapter]
An optically recording velocity interferometer system has been used to measure acceleration histories and maximum velocities for laser-driven aluminum foil targets launched from the output face of optical fibers. Peak flyer velocities have been determined as a function of various parameters, including driving laser fluence, laser pulse duration and target thickness. The results at high fluences are consistent with a nearly constant efficiency of coupling optical energy into flyer kinetic energy and a small ablated mass fraction; however, the coupling efficiency falls off rapidly at fluences < 15 J-cm -2 . Measurement of the time delay between laser pulse arrival at the target and the onset of flyer motion have also been performed. Significant delays are observed at low fluences, arising from the increased time required for plasma formation at the fiber/foil interface under these conditions.
440600 -- Optical Instrumentation-- (1990-)↗
Parametric Sensitivity Comparison of Simulation Models for Flyer Plate Impact Experiments
This paper compares the sensitivities of different modeling approaches for fundamental flyer plate impact experiments to variations of several input parameters. Two modeling approaches are used to model a copper flyer plate experiment: the CTH hydrodynamic code and the LS-DYNA code using the smoothed particle hydrodynamic (SPH) approach. Simulations using these two methods are compared to experimental data from a gas gun experiment in which a copper flyer plate impacted a copper target plate. The experiment was designed to cause spall in the target. Numerical simulations are conducted using typical input physics models including the Mie-Grüneisen equation of state, the Johnson-Cook compressive strength model, and a pressure cutoff (Pmin) model for tensile damage (spall). Effects of artificial viscosity, spall strength, and computational cell size are studied and discussed with the objective of improving the accuracy of these simulations.
CTH, smoothed particle hydrodynamics, SPH, Johnson↗
Variable stiffness flyer plate for penetration device
A penetration device including a casing, a propellant positioned in the casing, and a flyer plate. The flyer plate is coupled to the casing and adjacent to the propellant. The flyer plate includes a center portion having a substantially constant first thickness and includes a peripheral portion around the center portion and defining an edge. The peripheral portion includes one or more recesses in a first surface of the peripheral portion.
Muha, Nicholas B.↗
Variables Affecting Smooth Particle Hydrodynamics Simulation of High-Velocity Flyer Plate Impact Experiments
This paper describes our work to characterize the variables affecting the smoothed particle hydrodynamics (SPH) method in the LS-DYNA package for simulating high-velocity flyer plate impact experiments. LS-DYNA simulations are compared with one-dimensional experimental data of an oxygen-free high-conductivity (OFHC) copper flyer plate impacting another plate of the same material. The comparison is made by measuring the velocity of a point on the back surface of the impact plate using the velocity interferometer system for any reflector (VISAR) technique.
smoothed particle hydrodynamics, SPH, flyer plate ↗