The authors are developing the Ranchero high explosive pulsed power (HEPP) system to power cylindrically imploding solid-density liners for hydrodynamics experiments. The near-term goal is to conduct experiments in the regime pertinent to the Atlas Capacitor bank. That is, they will attempt to implode liners of (approximately)50 g mass at velocities approaching 15 km/sec. The basic building block of the HEPP system is a coaxial generator with a 304.8 mm diameter stator, and an initial armature diameter of 152 mm. The armature is expanded by a high explosive (HE) charge detonated simultaneously along its axis. They have reported a variety of experiments conducted with generator modules 43 cm long and have presented an initial design for hydrodynamic liner experiments. In this paper they give a synopsis of their first system test, and a status report on the development of a generator module that is 1.4 m long.
The authors are currently developing a high explosive pulsed power system concept that they call Ranchero. Ranchero systems consist of series-parallel combinations of simultaneously initiated coaxial magnetic flux compression generators, and are intended to operate in the range from 50 MA to a few hundred MA currents. One example of a Ranchero system is shown here. The coaxial modules lend themselves to extracting the current output either from one end or along the generator midplane. They have previously published design considerations related to the different module configurations, and in this paper they concentrate on the system that they will use for their first imploding liner tests. A single module with end output. The module is 1.4-m long and expands the armature by a factor of two to reach the 30-cm OD stator. The first heavy liner implosion experiments will be conducted in the range of 40--50 MA currents. Electrical tests, to date, have employed high explosive (HE) charges 43-cm long. They have performed tests and related 1D MHD calculations at the 45-MA current level with small loads. From these results, they determine that they can deliver currents of approximately 50 MA to loads of 8 nH.
High explosive pulsed power (HEPP) techniques can address a wide range of pulsed power needs. The basis for HEPP techniques is the use of high explosives to reduce the inductance of a current-carrying circuit, thus multiplying the current due to magnetic flux conservation. For the past twenty years at Los Alamos, our high energy density physics (HEDP) program has followed a path leading to more sophisticated and higher current (and often power) systems. Twenty years ago, we had the capability of conducting tests at 10, or even 30 MA, with no power conditioning and low inductance loads. The time scale of the experiment was the time it took to compress the flux explosively, and our fastest generator with high current capability was a plate generator. The operating time of the generator is less than 15 [mu]s, and flux loading requires either an additional ≈60 [mu]s or a reduced-efficiency inductive coupling scheme. We could also deliver shortened pulses to select loads by completing our generator circuit, initially, with a relatively high inductance circuit element, then switching in a lower inductance with 2-3 [mu]s left of the generator pulse. Figure 1 shows the results of such a test. The test was conducted in 1974 to investigate our capability to drive plasma z-pinch experiments for the production of soft x-rays, and was a pulsed power success. However, our understanding of vacuum power flow issues was not mature enough at that time to design a functioning plasma z-pinch load. There was a renewed need for such a system in 1980, and at that time we began assembling a complete set of techniques required for success. We first fielded a baseline test using a simplified version of the HEPP system that generated the Figure 1 data. Subsequent tests followed a 'bite size' philosophy. That is, we first designed a complete system for a level of complexity at which we believed success could be achieved. We conducted tests of that system, and once it was working in all respects, we designed the next generation system. The ultimate goal of this process was to develop a source of ≈1 MJ of soft x-rays. The process culminated, after the development of two intermediate level systems, with the development of the Procyon system. This system produced x-ray pulses of up to 1.7 MJ at temperatures up to 97 eV. Following those experiments, our attention turned to powering solid-density z-pinch liners, requiring even higher current systems. At Los Alamos, we developed the Ranchero system for that purpose, and we have collaborated with HEPP experts in Russia to power similar liner loads using disk generator systems. Our Ranchero system includes a module tested at ≈50 MA, that should operate easily at 70-90 MA. We designed Ranchero to allow modules arrayed in parallel to generate currents over 200 MA, and we are confident that we can do experiments now at 50-200 MA in the same way that we could do tests at 10-30 MA with plate generators 20 years ago. We have recently stepped back from our quest for higher energy and power systems to consider what applications we can address using relatively low cost plate generators coupled with advances achieved in our HEDP system development. We will describe relevant HEPP components, and discuss two promising applications.
A key element in the design of a coaxial generator system is the simplicity of the geometry. The clean cylindrical geometry allows us a reasonable chance at modeling RANCHERO performance using our 1D and 2D MHD modeling codes. The results of numerical simulations have been compare to several tests of the RANCHERO system in a variety of configurations. Recent comparisons of 1D calculations with the REOT-2 data have been extremely good and suggest that the generator is behaving in a very 1D like nature until reaching 90-95% of peak current. Differences between calculated current and measured performance during the last 3 mm (out of 70 mm) of flux compression may be a consequence of either the EOS for SF6, 2D effects, or both. This study will examine the existing models and attempt to provide a robust integrated model which can then be used to drive design studies, pre- and post-shot analysis, and predict performance parameters for slight variations of the base design of RANCHE RO.
The generation of megagauss fields for science and technology is an exciting area at the extremes of parameter space, involving the application and controlled handling of extremely high power and energy densities in small volumes and on short time scales. New physical phenomena, technological challenges, and the selection and development of materials, together create a unique potential and synergy resulting in fascinating discoveries and achievements. This book is a collection of the contributions of an international conference, which assembled the leading scientists and engineers worldwide working on the generation and use of the strongest magnetic fields possible. Other research activities include generators that employ explosives to create ultra-high pulsed power for different applications, such as megavolt or radiation sources. Additional topics are the generation of plasmas and magnetized plasmas for fusion, imploding liners, rail guns, etc.
Research on topics requiring high magnetic fields and high currents have been pursued using high explosive pulsed power (HEPP) techniques since the 1950s at Los Alamos National Laboratory. We have developed many sophisticated HEPr systems through the years, and most of them depend on technology available from the nuclear weapons program. Through the 1980s and 1990s, our budgets would sustain parallel efforts in zpinch research using both HEPr and capacitor banks. In recent years, many changes have occurred that are driven by concerns such as safety, security, and environment, as well as reduced budgets and downsizing of the National Nuclear Security Administration (NNSA) complex due to the end of the cold war era. In this paper, we review the teclmiques developed to date, and adaptations that are driven by changes in budgets and our changing complex. One new Ranchero-based solid liner z-pinch experimental design is also presented. Explosives that are cast to shape instead of being machined, and initiation systems that depend on arrays of slapper detonators are important new tools. Some materials that are seen as hazardous to the environment are avoided in designs. The process continues to allow a wide range of research however, and there are few, if any, experiments that we have done in the past that could not be perform today. The HErr firing facility at Los Alamos continues to have a 2000 lb. high explosive limit, and our 2.4 MJ capacitor bank remains a mainstay of the effort. Modem diagnostic and data analysis capabilities allow fewer personnel to achieve better results, and in the broad sense we continue to have a robust capability.
In 1980, Los Alamos formed the 'Megajoule Committee' with the expressed goal of developing a one Megajoule plasma radiation source. The ensuing research and development has given rise to a wide variety of high explosive pulsed power accomplishments, and there is a continuous stream of work that continues to the present. A variety of flux compression generators (FCGs or generators) have been designed and tested, and a number of pulse shortening schemes have been investigated. Supporting computational tools have been developed in parallel with experiments. No fewer that six unique systems have been developed and used for experiments. This paper attempts to pull together the technical details, achievements, and wisdom amassed during the intervening thirty years, and notes how we would push for increased performance in the future.
We have conducted three tests of a new pulsed power device called the Full Function Test (FFT). These tests represented the culmination of an effort to establish a high energy pulsed power capability based on high explosive pulsed power (HEPP) technology. This involved an extensive computational modeling, engineering, fabrication, and fielding effort. The experiments were highly successful and a new US record for magnetic energy was obtained.
