S. Coffey

Design, fabrication, and operation of a high-energy liner implosion experiment at 16 megamperes

We discuss the design, fabrication, and operation of a liner implosion system at peak currents of 16 MA. Liners of 1100 aluminum, with initial length, radius, and thickness of 4 cm, 5 cm, and 1 mm, respectively, implode under the action of an axial current, rising in 8 /spl mu/s. Fields on conductor surfaces exceed 0.6 MG. Design and fabrication issues that were successfully addressed include: Pulsed Power-especially current joints at high magnetic fields and the possibility of electrical breakdown at connection of liner cassette insulator to bank insulation; Liner Physics-including the angle needed to maintain current contact between liner and glide-plane/electrode without jetting or buckling; Diagnostics-X-radiography through cassette insulator and outer conductor without shrapnel damage to film.

Flux Compression Generator Development at the Air Force Research Laboratory

The Air Force Research Laboratory (AFRL) maintains an extensive capability for the design, analysis, construction and testing of explosive pulsed power (EPP) components. Three flux compression generators (FCGs) were designed as part of an EPP technology development effort sponsored by AFRL and the Defense Advanced Research Projects Agency (DARPA). A secondary-stage, high-current FCG was designed to deliver 10 MA into a nominal load inductance of 80 nH from an initial generator inductance of 1.6 muH that is seeded with 1 MA. We have also developed a coaxial FCG to deliver more than 20 MA into a 2 nH load. The initial flux in the coaxial chamber (60 nH at 1.5 MA) is compressed uniformly using a copper armature, which is simultaneously initiated using a slapper detonator. Either of these two FCGs can be seeded with a third generator design: a high-gain, helical FCG. This model serves as our workhorse generator capable of delivering 2 MA into a 0.5 muH inductive load. It has also been operated into load inductances ranging from 0.1 to 2.0 muH with comparable flux delivery. All experiments are conducted on an explosive test range located on Kirtland Air Force Base [1]. The design effort is supported by powerful computer modeling using CAGEN [2], CALE and MACH2. Design features for all three FCGs are presented in this paper with results from recent explosive tests.

The Explosive Pulsed Power Test Facility at AFRL

The Air Force Research Laboratory has developed and tested a variety of explosive driven pulsed power devices over the past twenty-two years. Testing is performed primarily at a dedicated facility located at Chestnut Site on Kirtland Air Force Base. The facility is described in this paper, including details of recent upgrades.

Fiber-Optic Systems at the Explosive Pulsed Power Test Facility at AFRL

The Air Force Research Laboratory (AFRL) located on Kirtland Air Force Base performs explosive pulsed power experiments [1] - [3]. The large separation distances between the related subsystems of these shots increase the likelihood of inadvertent multiple electrical ground connections. This paper describes some of the fiber-optic devices routinely used during our explosive power tests to mitigate the problems associated with ground loops.

Parallel Triggering and Conduction of Rail-Gap Switches in a High-Current Low-Inductance Crowbar Switch

The field-reversed configuration heating experiment (FRCHX) was designed to form closed-field-line magnetized target plasmas for magnetoinertial fusion and other high energy density plasma research. These plasmas are in a field-reversed configuration and are formed via a reversed-field theta pinch on an already magnetized background plasma. To extend the duration and temporal uniformity of the pinch, the capacitor bank driving the reversed-field discharge is crowbarred near the current peak. Four parallel rail-gap switches are used on the FRCHX for this application to ensure a low-inductance crowbar discharge path and to accommodate the large magnitude of the discharge current (often greater than 1 MA). Historically, parallel operation of spark gap switches in a crowbarring arrangement has often proved to be difficult due to the very low voltage present on the bank and across the switches at the time of peak current. In a low-inductance design, triggering can be further complicated by the rapid collapse of what little voltage there is across the switches as soon as the first spark gap begins conduction. This paper reports on the efforts that were made to develop a low-inductance crowbar switch for the FRCHX and to ultimately enable successful triggering and operation of the four parallel rail-gap switches used in the crowbar. The design of the low-inductance parallel switch assembly is presented first, followed by a description of the triggering scheme employed to ensure conduction of all four switches.

Hardware and software upgrades for the saturn data acquisition triggers and time base (work supported by the Dept. of Energy)

This paper summarizes the recent changes to the hardware and software systems associated with the diagnostic digitizer triggers and their data acquisition control program at the Saturn pulsed power facility at Sandia National Laboratories. The main screen room contains approximately 70 digitizing scopes for monitoring 6 voltage or current probes along each of its 36 energy storage and transmission lines. Each module locates probes along its length in an identical fashion so that by comparing the timing of similar probes on each line, a measure of the power flow time symmetry can be obtained. The probes from each line are recorded in scope groupings, each containing 36 channels. In numerous cases, the archived group time bases were not correctly quantified with respect to the other scope groupings. This was problematic when comparing signals from different scope groupings. The source of the errors was found to be how the scope groupings were triggered as well as a software error associated with two models of digitizers. We have implemented changes so that all scope groupings are time tied to a common reference.

Performance of a compact, cascade FCG system

A system of two FCGs coupled via “flux-trapping” is described. The driver FCG, designated SAM, was custom-designed for this application. The output of SAM is a single-turn loop that is tightly coupled to the first winding section of a larger FCG, designated JILL. The single-turn driver loop, coupled to 35 turns of the input winding of JILL, provides a calculated flux gain of 28.