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Exploding Bridge Wire /EBW/ is treated as a transmission line system and pulse reflection techniques are used for checking the electrical integrity of an EBW cartridge. A step voltage is propagated into the system and the reflected voltage waves are monitored.
Pentaerythritol tetranitrate (PETN) is one of the most commonly used explosives for both military and mining applications. PETN is used in EBW (exploding bridge wire) and EFI (exploding foil initiator) detonator devices. Due the widespread usage of PETN, studies focusing on how the explosive changes with age, primarily its function in detonators has received particular interest. Aging studies have identified several factors that affect PETN detonator function over time, most notably the specific surface area of the explosive powder. Though small-scale studies have been performed on specific detonator systems with isolated batches of material, what is missing is a large statistically-significant study focusing on PETN aging characteristics - such as powder coarsening - and their influence on detonator performance. Herein we report the first large statistically viable PETN aging study focusing on four batches of PETN powder from the same stock of PETN using two stabilizers, polysaccharide and TriPEON. PETN was aged both as a free-flowing powder as well as in modified EBW RP-2 detonators, for one month at 75 °C. The PETN powder has been analyzed chemically using Fisher specific surface area analysis, SEM imaging and light scattering particle size analysis. Additionally the detonators were tested for performance through voltage-sweep threshold testing and function time measurements. Findings from the study indicate that aging at 75 °C for one month significantly changes the specific surface area and particle size of unstabilized PETN, leading to increases in detonator function time, but not detonator threshold values. Powders stabilized with TriPEON displayed less significant increases in function time, while powder stabilized with polysaccharide exhibited no aging effects, despite the high temperature aging.
Operability thresholds that differentiate between functional RP-87 exploding bridge wire (EBW) detonators and nonfunctional RP-87 EBW detonators (duds) were determined by measuring the time delay between initiation and early wall movement (function time). The detonators were inserted into an externally heated hollow cylinder of aluminum and fired with current flow from a charged capacitor using an exploding bridge wire (EBW initiated). Functioning detonators responded like unheated pristine detonators when the function time was 4 μs or less. The operability thresholds of the detonators were characterized with a simple decomposition cookoff model calibrated using a modified version of the Sandia Instrumented Thermal Ignition (SITI) experiment. These thresholds are based on the calculated state of the PETN when the detonators fire. The operability threshold is proportional to the positive temperature difference (ΔT) between the maximum temperature within the PETN and the onset of decomposition (~406 K). Furthermore, the temperature difference alone was not sufficient to define the operability threshold. The operability threshold was also proportional to the time that the PETN had been at elevated temperatures. That is, failure was proportional to both temperature and reaction rate. The reacted gas fraction is used in the current work for the reaction correlation. Melting of PETN also had a significant effect on the operability threshold. Detonator failure occurred when the maximum temperature exceeded the nominal melting point of PETN (414 K) for 45±5 s or more.
Exploding Bridge Wire (EBW) is an important design for initiating detonators relevant to several LLNL systems. In such designs, a metal bridge wire is in direct contact with a porous secondary high explosive (HE), typically pressed to around 50% of its crystalline density. Initiation is believed to occur through shock waves generated when the bridge wire is made to explode via the rapid passing of a strong current pulse. Permeametry is an important characterization tool for the porous powdered HE (PETN, HMX, etc.) component in such devices. Such powders are well known to coarsen with age, with an accompanying deterioration in performance, which includes increased function time and sensitivity. Among various material characteristics, one that has been shown to correlate the most with such performance parameters is the flow-permeable surface area (FSSA), measured using air-permeametry. Commercially available permeametry apparatuses, such as that from Fisher Scientific or a more modern version from Micromeritics suffer from a few drawbacks, most notably as related to monitoring age-related changes in FSSA. This is because it requires re-compaction of the aged powder into the permeametry tube, which in most cases leads to an unwanted increase in FSSA. To address this and a few other shortcomings, we have been developing a modern version of the permeameter, Gee-Reinstein-Maiti Modern Air-Permeametry System (GRM-MAPS). In this report, we summarize progress made in FY25 toward perfecting and calibrating the instrument, which we aim at deploying within surveillance in FY26.
Abstract The particle velocity created in beds of both low-density inert sugar and explosive PETN as a function of distance from an exploding bridgewire was measured using optical velocimetry and a silvered PMMA window. As expected, more violent bridge-bursts (from a greater-stored-energy capacitive discharge unit) resulted in greater particle velocities and a better supported compaction wave in sugar. In all cases, ramp waves, not shocks, were observed in the inert sugar. Large window velocities were observed for very powerful bursts (up to 270 m/s), but bursts required for stochastic detonator operation conditions resulted in sugar/PMMA window velocities of only 8–10 m/s 0.85 mm from the bridge location. In contrast, after a distance of only 0.65 mm, a building shock wave was observed in PETN under both threshold and reliable firing conditions. Subsequently a hot-spot-driven shock-to-detonation (SDT) process was observed prior to full detonation. The measured buildup process accounts for $$\approx $$ ≈ 66% of the so-called excess transit time (ETT) between the observed and theoretical total function time for the particular exploding-bridge-wire (EBW) detonator studied. The remainder must occur in the powerful output pellet region. In contrast to a common understanding, the ETT is found to be a weak function of the discharge energy. Thus, the operation of the detonator after a bridge-burst energy-to-powder reaction transition process is found to be hot-spot-driven SDT in both the low- and high-density pellets.
In the present study, commercially available detonators with pentaerythritol tetranitrate (PETN) were subjected to elevated temperatures. The detonators were thermally ignited over a range of heating rates to measure ignition delay time and assess detonator violence. The violence of the detonator was quantified by measuring the velocity of the detonator closure disc (or “flyer”). The maximum flyer velocity of a thermally ignited detonator was comparable in magnitude to that obtained by initiating a room temperature pristine detonator with an exploding bridge wire (under the same confinement); however, the high flyer velocity was not an indication of deflagration to detonation transition (DDT) in the thermally ignited detonator. The detonator responded more violently than a thermally ignited detonator when initiated at 95% of the ignition delay time. Furthermore, inoperability thresholds were also measured by varying the detonator temperature and the threshold was found to be sensitive at detonator temperatures below the melting point of PETN.
Dielectric breakdown is an example of a natural phenomenon that occurs on very short time scales, making it incredibly difficult to capture optical images of the process. Event initiation jitter is one of the primary challenges, as even a microsecond of jitter time can cause the imaging attempt to fail. Initial attempts to capture images of dielectric breakdown using a gigahertz frame rate camera and an exploding bridge wire initiation were stymied by high initiation jitter. Subsequently, a novel optical delay line apparatus was developed in order to effectively circumvent the jitter and reliably image dielectric breakdown. Here, the design and performance of the optical delay line apparatus are presented. The optical delay line increased the image capture success rate from 25% to 94% while also permitting enhanced temporal resolution and has application in imaging other high-jitter, extremely fast phenomena.
The present work investigates high initial pressure detonations of a stoichiometric mixture of ethylene and nitrous oxide (C2H4 + 6N2O) as a method of fracturing rock beneath the ground surface. These tests were conducted at a test site operated by the Energetic Materials Research and Testing Center (EMRTC), Socorro, New Mexico. The volume under the surface used for testing (called the Down Hole Assembly) consists of a 0.438 in. ID x 50 ft. long stainless-steel tube running down from the test site to a well bore which is 3 in. ID x 10 ft. long and the rock in the well bore is exposed to the propagating combustion wave. The testing carried out at Zucrow Laboratories in the smaller, alloy steel combustion vessel provided a scaling of pressures expected in the well bore. The combustion is initiated by energizing an EBW (Exploding Bridge Wire) above the ground surface. The experimental setup accommodates one high pressure (100,000 psia) transducer to measure the pressure peak and is placed approximately 5 ft. above the ground surface and 5 ft. downstream of the EBW. The focus of this series of experiments is to investigate the dependence of fracture to the rock beneath the surface on initial pressures of the mixture of ethylene and nitrous oxide. Experiments were carried out at initial pressures varying between 125 psia and 300 psi. The transducer recorded elevated pressures, which were 2.3 to 2.6 times in excess of the CJ values. The experimental results are discussed and explained in this report.
A survey, analysis, and testing of available cable connector configurations were carried out in connection with transmission of high voltage/current to an exploding wire bridge. Transmission was desired at high efficiency with maximum cable flexibility, at minimum weight and size of the cable connector, with maximum cable length while maintaining applicable voltage/current pulse characteristics, and with due consideration to environmental parameters.
Abstract not provided.
Electrically exploded wires find uses throughout high-energy physics. For example, they are commonly used as high-temperature sources, X-ray generators, and in precision timing detonators. However, the detailed and complete physics that occurs is complex and still poorly understood. A full mechanistic description of these complex phenomena is beyond the scope of a single paper. Instead, we focus on the formation of metal vapor and its transition to plasma. This single transition is commonly assumed to comprise “bridge-burst”. We use a suite of diagnostics including a novel, fiber-based, high-speed, optical pyrometer to better characterize this transition. The primary finding from this project is that peak light output from an exploding wire does not temporally match the peak temperature. Additionally, it is found that peak light does not align with peak bridge-burst voltage and that the peak temperature is not voltage-dependent. These findings are non-intuitive and will allow for the correction of false assumptions previously made about this topic.