Modern Pulsed Power: Charlie Martin and Beyond

International Symposium on New Paradigm VLSI Computing, Sendai, Japan, Dec. 12-14, 2002, pp.31-36.This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, may not be copyrighted.Modern pulsed power has its genesis in the pioneering work of the late John Christopher Martin and his colleagues at the Atomic Weapons Establishment, Aldermaston, U.K., in the 1960s [1]. “Charlie,” as he was known to the community, was a hydrodynamicist who was frustrated by his inability to purchase an adequate X-ray radiography source to image the dynamic phenomena he was interested in. As a result, he pursued a new generation of radiography sources that were based on high-power Marx generators, coupled with low-impedance transmission lines, and cold cathode single-stage accelerating gaps. Thus was the birth of modern pulsed power.U. S. Army Research OfficeSponsor/Monitor's Report Number(s):42713.8-PHDAAD19-01-1-069

A Laboratory Investigation of Supersonic Clumpy Flows: Experimental Design and Theoretical Analysis

We present a design for high energy density laboratory experiments studying the interaction of hypersonic shocks with a large number of inhomogeneities. These ``clumpy'' flows are relevant to a wide variety of astrophysical environments including the evolution of molecular clouds, outflows from young stars, Planetary Nebulae and Active Galactic Nuclei. The experiment consists of a strong shock (driven by a pulsed power machine or a high intensity laser) impinging on a region of randomly placed plastic rods. We discuss the goals of the specific design and how they are met by specific choices of target components. An adaptive mesh refinement hydrodynamic code is used to analyze the design and establish a predictive baseline for the experiments. The simulations confirm the effectiveness of the design in terms of articulating the differences between shocks propagating through smooth and clumpy environments. In particular, we find significant differences between the shock propagation speeds in a clumpy medium compared to a smooth one with the same average density. The simulation results are of general interest for foams in both inertial confinement fusion and laboratory astrophysics studies. Our results highlight the danger of using average properties of inhomogeneous astrophysical environments when comparing timescales for critical processes such as shock crossing and gravitational collapse times.Comment: 7 pages, 6 figures. Submitted to the Astrophysical Journal. For additional information, including simulation animations and the pdf and ps files of the paper with embedded high-quality images, see http://pas.rochester.edu/~wm

Concept of a novel fast neutron imaging detector based on THGEM for fan-beam tomography applications

The conceptual design and operational principle of a novel high-efficiency, fast neutron imaging detector based on THGEM, intended for future fan-beam transmission tomography applications, is described. We report on a feasibility study based on theoretical modeling and computer simulations of a possible detector configuration prototype. In particular we discuss results regarding the optimization of detector geometry, estimation of its general performance, and expected imaging quality: it has been estimated that detection efficiency of around 5-8% can be achieved for 2.5MeV neutrons; spatial resolution is around one millimeter with no substantial degradation due to scattering effects. The foreseen applications of the imaging system are neutron tomography in non-destructive testing for the nuclear energy industry, including examination of spent nuclear fuel bundles, detection of explosives or drugs, as well as investigation of thermal hydraulics phenomena (e.g., two-phase flow, heat transfer, phase change, coolant dynamics, and liquid metal flow).Comment: 11 Pages; 6 Figures; Proceeding of the International Workshop on Fast Neutron Detectors and Application FNDA2011, Ein Gedi, Israel, November 2011. Published on the Journal of Instrumentation; 2012 JINST 7 C0205

Research opportunities with compact accelerator-driven neutron sources

Since the discovery of the neutron in 1934 neutron beams have been used in a very broad range of applications, As an aging fleet of nuclear reactor sources is retired the use of compact accelerator–driven neutron sources (CANS) are becoming more prevalent. CANS are playing a significant and expanding role in research and development in science and engineering, as well as in education and training. In the realm of multidisciplinary applications, CANS offer opportunities over a wide range of technical utilization, from interrogation of civil structures to medical therapy to cultural heritage study. This paper aims to provide the first comprehensive overview of the history, current status of operation, and ongoing development of CANS worldwide. The basic physics and engineering regarding neutron production by accelerators, target-moderator systems, and beam line instrumentation are introduced, followed by an extensive discussion of various evolving applications currently exploited at CANS

The use of pulsed power driven underwater electrical wire explosions for high velocity flyer plate acceleration

This thesis describes a new method to accelerate flyer plates for high-pressure experiments utilising the pulsed power driven explosion of a planar wire array submerged in a water bath as a pressure source. The typical acceleration dynamics of such a system are described, including the contribution of magnetic acceleration via induced current and shock reverberation in an aluminium flyer plate. Maximum usable velocity achieved from a peak current of 550 kA was 1100 m/s. Analysis of the shocks in water and aluminium indicate a particle velocity in the water of 1020 m/s and shock pressure in the water of ~ 3 GPa, leading to shock pressure in the aluminium of 7 GPa. 3D and 2D MHD simulations of this system, performed using the GORGON MHD code, are also discussed, allowing calculation of shock properties and uniformity as they propagate through the water and plate, showing reasonable agreement with experiment up to shock breakout. We have experimentally demonstrated a configuration for the use of such a flyer in a shock experiment setup, and found that the explosion of a foil appears to produce similar results to a wire array with similar properties. To further understand the underlying effects behind this wire explosion, we have performed experiments performed at the ESRF synchrotron performing radiography on exploding wires. These allowed us to map the position of the shock front and expanding wire material against time, and verify the shock launch time relative to the resistive voltage temporal profile. We also describe experiments performing radiography along the axis of a cylindrical array, showing the formation of secondary and tertiary shocks and their significance in balancing a corrugated shock front generated by the explosion of discrete wires into a smooth shock front. In all cases, we compare the results of these experiments to magnetic stripline flyer plates accelerated with the same machine. ~ 2× greater maximum usable velocity was achieved using magnetically accelerated flyer plates, but promise is shown for using underwater electrical wire explosions to accelerate larger area, thicker plates.Open Acces