Loads for Pulsed Power Cylindrical Implosion Experiments

The discipline of pulsed power hydrodynamics is a new application of low-impedance, pulsed power technology, developed to study implosion hydrodynamics, instabilities, turbulence, and material properties in a highly precise, controllable environment at the extremes of pressure and material velocity. The discipline of pulsed power hydrodynamics arose in response to the need for economical, high-precision data to validate sophisticated numerical models used in current numerical simulations and to motivate the development of new models for future simulations. The international capability in pulsed power technology that has evolved over several decades in response to numerous other programmatic needs played a pivotal role in the development of the new discipline by enabling demonstrations of the techniques and production of introductory data long before a dedicated facility could be conceived, planned, and built. The high-precision, cylindrically imploding liner is the tool most frequently used to convert electromagnetic energy into the hydrodynamic (particle kinetic) energy needed to drive strong shocks, quasi-isentropic compression, or large volume adiabatic compression for the experiments. At typical parameters, a 30-gr, 1-mm- thick liner with an initial radius of 5 cm, driven by a current of 20 MA, can be accelerated to 7.5 km/sec producing mega-bar shocks in medium density targets. Velocities up to 20 km/sec and pressures >20 Mbar in high density targets are possible. The Atlas facility, designed and built by Los Alamos, houses the world's first laboratory pulsed power system designed specifically to explore this relatively new family of pulsed power applications. Constructed in the year 2000 and commissioned in August 2001, Atlas is a 24-MJ, high-performance capacitor bank delivering currents up to 30 Megamperes with a rise time of 5 to 6 musec. The first Atlas liner implosion experiments were conducted in September 2001, and 16 experiments were conducted in the first year of operation before Atlas was disassembled to be moved to the Nevada Test Site, where experiments began again in July 2005. Applications of pulsed power hydrodynamics techniques currently include material property topics such as: exploration of material strength at high rates of strain; material failure including fracture, damage, and spall; and interfacial dynamics at high relative velocities and high interfacial pressures. Implosion dynamics and a variety of complex hydrodynamic geometries have been explored and experiments to explore perturbation growth and transition to turbulence are under consideration. Longer term applications include the study of the behavior and properties of strongly coupled plasmas and the equation of state of metals and non-metals at pressures above 10 Mbar. This paper will provide an overview of the programmatic evolution that led to the birth of the discipline of pulsed power hydrodynamics.

Switched mode pulse power supply is a promising technique for high-power quasi-continuous laser driver. Contrast to lossy linear laser drivers, switched mode laser drivers can achieve higher efficiency. However, many challenges have been proposed, such as fast pulse edge, low current ripple. This paper proposes a multiphase interleaved pulse power supply with energy recovery and inductive storage (MIEF-PPS). The basic concept of the topology is the inclusion of a multiphase converter with pulse forming circuits to the converter system, which decouples the current slew rate and current ripple. Using an inductive storage technology and pulse forming circuits, a shorter pulse current rising time is obtained. The inductor energy is fed back to the input source not discharged to the load, resulting in a fast pulse trailing edge and energy saving. Thus the pulse current response observed when using this proposed technique is found to be much faster when compared to the conventional interleaved buck driver. Moreover, a pre-charge method is proposed to overcome the challenge of digitally controlling the inductive storage. The proposed topology was simulated in MATLAB/Simulink and validated against the experimental results of a laboratory prototype, 360 W dual-interleaved pulsed power supply.

There is a growing need for supplying repetitive pulsed power loads of increasing magnitudes up to several hundred megawatts or more in areas of radar, lasers, high-energy physics experiments and thermonuclear fusion. The nature of such loads can be expected to be as diverse as their applications. The pulsed power demands and corresponding reactive volt-amperes requirements are undesirable from the frequency and voltage fluctuation standpoint, even for the large utility power systems. Techniques for supplying large dc-pulsed loads from a relatively small size ac generator by means of inductive storage and the capacitor commutated converters are presented. A theoretical basis is provided for analyzing the converters which serve to minimize the effects of pulsed power and corresponding reactive volt-amperes. Energy transfer between the storage inductor and the pulsed load is permitted with minimal loss, at a readily controllable rate including the reversibility of power in case of inductive loads. Use of a simple control scheme is shown to provide a precise load voltage regulation which may be a requirement for certain applications. The greatest use of these circuits would be in supplying loads with pulse durations of a few milliseconds to many seconds or minutes.

Summary form only given. Pulsed power hydrodynamics is a new application of pulsed high magnetic fields to explore advanced hydrodynamics, instabilities, fluid turbulences, and material properties in a highly precise, controllable environment at the extremes of pressure and material velocity. The Atlas facility designed and built by Los Alamos is the world's first and only laboratory pulsed power system designed specifically to explore this relatively new family of pulsed power applications. Constructed in 2000 and commissioned in August 2001, Atlas is a 24-MJ high-performance capacitor bank delivering up to 30-megamperes with a current risetime of 5-6-musec. The high-precision, cylindrical, imploding liner is the tool most frequently used to convert electromagnetic energy into the hydrodynamic (particle kinetic) energy needed to drive the experiments. For typical liner parameters with an initial radius of 5-cm, the peak current of 30-MA delivered by Atlas results in magnetic fields just over 1-MG outside the liner prior to implosion. During the 5 to 10-musec implosion, the field outside the liner rises to several MG in typical situations. At these fields the rear surface of the liner is melted and it is subject to a variety of complex behaviors including: diffusion dominated and/or melt wave field penetration and heating; magneto Rayleigh-Taylor sausage mode behavior at the liner/field interface; and azimuthal asymmetry due to perturbations in current drive. The first Atlas liner implosion experiments were conducted in September 2001 and 16 experiments were conducted in the first year of operation. Immediate applications of the new pulsed power hydrodynamics techniques include material property topics such as: exploration of material strength at high rates of strain, material failure including fracture and spall, and-interfacial dynamics at high relative velocities and high interfacial pressures. A variety of complex hydrodynamic geometries will be explored and experiments will be designed to explore unstable perturbation growth and transition to turbulence. Longer term applications include the study of the hydrodynamics and properties of strongly coupled plasmas and equation of state of materials at pressures above 10 Mbar. This paper will provide an overview of the Atlas system and of the range of problems to which pulsed power hydrodynamics can be applied and the issues associated with these techniques

This paper describes a new recycling method for metal-coated plastics. Pulsed power technology was used to remove a metal layer (aluminum) from CD-ROM. The progress of removal and the state of discharge were investigated in detail. In addition, the shadow picture method including a digital image processing was used to estimate removal amount. A pulsed power generator using magnetic pulse compression (MPC-PPG) with maximum storage energy of 40 J/pulse was used. Pulsed power was applied to concentric ring electrodes placed on the CD-ROM. Separation between electrodes was about 35 mm. Results show that almost all of the metal layer was removed under application of about 30 shots of pulse power. A strong correlation between the removed area measured by the shadow picture method and the removed mass was obtained, allowing the removed area and mass to be measured instantly by the shadow picture method. Furthermore, it was revealed that the discharge onset voltage increases with gap length between the electrodes and the aluminum layer left on the surface. Due to the surface flashover voltage between ring electrodes of about 80 kV, a pulsed power source output voltage larger than 80 kV is required.

Explosive formed fuses (EFFs) use conducting elements that are deformed by explosive pressure (typically, against dielectric dies). This causes the fuse geometry to change, so that the conducting element cross section decreases. This enables a higher ratio of current conduction to current interrupt time than for normal fuses, and it enables more control of when current interruption occurs. In combination with a suitable output closing switch, EFF's can be used to obtain several hundred kilovolt voltage pulses from inductive stores to drive several ohm loads. With proper choices of inductive store, EFF geometry and material, and output closing switch features, such a voltage pulse can be approximately flat topped for microsecond duration and have a small fraction of microsecond risetime. We present theoretical analysis and circuit simulations which illustrate this, using scaled empirical EFF parameters for inductive stores in the 1 weber flux, several hundred nanohenry range. The circuit simulations were done using MicroCap-IV, with user defined elements. These simulations were done with static inductive stores and with explosive magnetic flux compression generators driving inductive stores.

The Second International Conference and Advanced School 'Turbulent Mixing and Beyond', TMB-2009, was held at the Abdus Salam International Centre for Theoretical Physics, (ICTP), Trieste, Italy on 27 July–7 August 2009. TMB-2009 united over 180 participants ranging from students to members of the National Academies of Sciences and Engineering, and including researchers at experienced and early stages of their carriers from leading scientific institutions in academia, national laboratories, corporations and industry worldwide. Responding to the community's inquiry and reaffirming the practices established at TMB-2007, two Round Tables were organized for the participants of TMB-2009 on 30 July 2009 and 6 August 2009 in the Oppenheimer Room at the Centre. The goals of the Round Tables were to encourage the information exchange among the members of the interdisciplinary and international TMB community, promote discussions regarding the state-of-the-art in TMB-related scientific areas, identify directions for frontier research, and articulate recommendations for future developments.

Due to their high density of energy and low cost the inductive storages (IS) in combination with a high resource switch [1-4] have greater potential compared to the storage capacitors. Among their advantages is the generation of pulse series at high efficiency of energy transfer. In [5, 6] one of possible applications for the generators based on IS was proposed, namely generation of series of gigawatt power individual pulses with a pulse duration of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> sec and more. A rail launcher of macro-size bodies was taken as the load. The proposed variant of the generator and accelerator can be used to launch bodies of several kilograms at a pulse series of 5-10 pulses per second.The concepts suggested in [5, 6] are developed in the current work where a set of solutions are under consideration that allows the generation of a series of pulse trains to be produced. The pulse generator is based on a transformer IS with switching the turns of the secondary winding. A rail accelerator with its inductance of 1μH /m is used as the load and the duration of a single pulse in the train is to 2-3·10-4sec. The number of pulses in train is determined by the conditions of allowable spread of the operation current in the secondary winding of IS (~5%) and can vary from 100 to 150 pulses. Such an accelerator is intended to accelerate a macro-size body of an order of one gram. The work also presents a technical solution for interrupting a pulse train and renew the following train from the common sequence of train series. The common time interval between the trains is dependent on the time of switching over the turns in the IS secondary winding. This is performed with the goal to restore the current value and this time can vary within 11.5ms.

We report on the progress made to date for a Laboratory Directed Research and Development (LDRD) project aimed at diagnosing magnetic flux compression on the Z pulsed-power accelerator (0-20 MA in 100 ns). Each experiment consisted of an initially solid Be or Al liner (cylindrical tube), which was imploded using the Z accelerator's drive current (0-20 MA in 100 ns). The imploding liner compresses a 10-T axial seed field, B z ( 0 ) , supplied by an independently driven Helmholtz coil pair. Assuming perfect flux conservation, the axial field amplification should be well described by B z ( t ) = B z ( 0 ) x [ R ( 0 ) / R ( t )] 2 , where R is the liner's inner surface radius. With perfect flux conservation, B z ( t ) and dB z / dt values exceeding 10 4 T and 10 12 T/s, respectively, are expected. These large values, the diminishing liner volume, and the harsh environment on Z, make it particularly challenging to measure these fields. We report on our latest efforts to do so using three primary techniques: (1) micro B-dot probes to measure the fringe fields associated with flux compression, (2) streaked visible Zeeman absorption spectroscopy, and (3) fiber-based Faraday rotation. We also mention two new techniques that make use of the neutron diagnostics suite on Z. These techniques were not developed under this LDRD, but they could influence how we prioritize our efforts to diagnose magnetic flux compression on Z in the future. The first technique is based on the yield ratio of secondary DT to primary DD reactions. The second technique makes use of the secondary DT neutron time-of-flight energy spectra. Both of these techniques have been used successfully to infer the degree of magnetization at stagnation in fully integrated Magnetized Liner Inertial Fusion (MagLIF) experiments on Z [P. F. Schmit et al. , Phys. Rev. Lett. 113 , 155004 (2014); P. F. Knapp et al. , Phys. Plasmas, 22 , 056312 (2015)]. Finally, we present some recent developments for designing and fabricating novel micro B-dot probes to measure B z ( t ) inside of an imploding liner. In one approach, the micro B-dot loops were fabricated on a printed circuit board (PCB). The PCB was then soldered to off-the-shelf 0.020- inch-diameter semi-rigid coaxial cables, which were terminated with standard SMA connectors. These probes were recently tested using the COBRA pulsed power generator (0-1 MA in 100 ns) at Cornell University. In another approach, we are planning to use new multi-material 3D printing capabilities to fabricate novel micro B-dot packages. In the near future, we plan to 3D print these probes and then test them on the COBRA generator. With successful operation demonstrated at 1-MA, we will then make plans to use these probes on a 20-MA Z experiment.

Summary form only given, as follows. The first experiments conducted on the twenty-four megajoule capacitor bank, Atlas, are described. These experiments are intended to determine whether there are qualitative differences between phenomena in convergent and planar geometries. It is well known that spall, which arises as a result of intersecting release waves putting a material into tension, is a function of shock amplitude, shape, and duration. However, quantifying differences is difficult, and often the best one can do is to obtain the spall of the material. This important parameter is inferred from laser interferometry measurements (VISAR) of the pull back velocity of the free surface of a shocked sample. Principally, planar experiments are performed one of three ways: using a gas gun to launch a freeflying sabot into the target, employing a laser driven mini-flyer, or using high explosives to launch the shock wave. In the case of Atlas, the flyer is a cylindrically imploding metal liner, driven by the magnetic pressure produced by the bank current. After impact of the liner with the target the magnetic pressure continues to accelerate the liner/target assembly radially inward. This continued acceleration combined with converging geometry differentiates these experiments from those conducted in planar geometry. VISAR will be used to measure the free surface velocity of a shocked aluminum target, and the signature will be used to infer the strength and compare this with that obtained from gas gun experiments. Comparisons of the VISAR signals obtained on Atlas experiments with gas gun signals will be used to provide insight into the effects of convergence on phenomena. Axial radiography will also be fielded to determine the location of the spalled material layer, and correlate this with the VISAR.

Over the last few years a new application for high performance pulsed power technology has joined the family of traditional radiation source applications. This new application uses the magnetic fields from large current pulses to implode near-solid density cylindrical liners, with very high precision, for the study of material properties and hydrodynamics in complex geometries. The 24-MJ Atlas pulsed power system, operated since September 2001 in Los Alamos, has employed high-precision liners driven with currents up to 25 MA to conduct a variety of experiments involving the production of moderate to strong shocks to study material failure and the dynamic behavior of an interface at high relative velocities and high normal pressures and the compression of targets in complex geometries to validate sophisticated hydrodynamic simulations. This paper will describe the behavior of the initial liner implosions evaluating the physical cause for the perturbation growth and will describe the later, more uniform, implosions. The paper will attempt to address the physical behaviors that lead to different behaviors in each case.

Pulse power systems delivering in excess of 100 MJ represent one of the next major challenges to the pulse power community. Explosive pulse power systems using magnetic flux compression provide a direct path to such demonstrations. Furthermore, as energy requirements grow, single use explosive systems may represent the only affordable source of ultra-high energy environments. Currently two flux compressor configurations are under consideration for powering solid liner implosions at currents above 100 MA and at energies above 100 MJ. A simultaneously initiated coaxial flux compressor (Ranchero) is described in a companion paper. A modular, center initiated disk configuration, generally patterned after the DEMG is the other candidate. Either can drive loads directly or can conceptually be connected in parallel with flat plate transmission lines to increase current delivery. Phenomenological models and conceptual designs for DEMG systems have been previously reported. In this paper we report the results of the experimental test of a first generation disk generator system. Individual disk segments have been tested with framing camera diagnostics to evaluate overall performance, dynamics and fabrication failure points. In general no bulk failures were observed in several shots and the critical weld joints maintained their integrity for at least 4 /spl mu/s after arrival of the detonation front. Single module pulse power experiments have been conducted at reduced initial current (1.5-2.0 MA) with a fixed inductance load of 0.22 nH.

Compared with the capacitive pulsed power supply (CPPS), the inductive pulsed power supply (IPPS) is considered to have broader prospects because of its theoretically higher energy densities. Most recent researches focus on characteristics of the IPPS with a fixed load, which is rather different from practical applications from the engineering point of view. In this paper, with the purpose of preliminarily verifying the IPPS’s feasibility, the performance of the novel meat grinder circuit with a dynamic load model is presented and analysed under PSpice environment. The analysis model is based on the parameters of the four-module IPPS and the pulsed power load built in Institute of Electrical Engineering. Finally, the comparison between the IPPS and the CPPS with same initial energy is carried out.

Pulsed power systems for directed energy weapon platforms are becoming increasingly important in modern combat situations. A general thermodynamic analytical investigation was developed to assess the impact of technological improvements on mission effectiveness and weapon power generation in an aircraft (a/c) based pulsed power system. The power system, for which the analysis is being conducted, essentially consists of six major components, a prime power source, electrical power generator, power conditioner, pulsed power source and pulsed power processor and the thermal management system (TMS) with a total estimated payload restriction of 4600 kgs., based on a USAF cargo aircraft. The a/c based power systems analysis corresponds to a notional aircraft mission, with the turbo- shaft engine operating at a fixed altitude. It has been assumed that heat from various system components is collected by the same coolant loop, and then rejected to ambient air in a ram air heat exchanger (RAHX). The analysis was based on a Multi-MW class pulsed power source output and a notional mission profile with an engagement period of 60 minutes during which several duty cycle scenarios were considered. The power system components were sized to accommodate the power requirement represented by the respective duty cycle of operation. Several power system architectures were evaluated with a baseline power system model that incorporated current off-the-shelf (OTS) technologies for each component. The baseline power systems analysis was conducted to size a power system for steady state operation at peak load during an individual engagement. A stand-alone turbo shaft engine was used as the primary power source because of its high power density but the engine performance is very sensitive to increasing altitude where the output power diminishes rapidly. As a result of this and the necessity to accommodate load sharing or load following during engagement, the investigations were extended to the hybrid power system architecture with turbo alternator-battery and turbo alternator-flywheel combinations.

Vladislav Nikolaevich Mokhov, an outstanding scientist, Doctor of Science in Physics and Mathematics, professor, died on December 27, 2011 after long time of severe disease. Before this illness he was Deputy Scientific Leader of the All-Russian Research Institute of Experimental Physics (VNIIEF). V.N. Mokhov was born on April 12, 1931 in the town of Atkarsk, Saratov region, Russia. In 1955, after graduation from the Moscow Engineering Physics Institute, he in a group of the most brilliant and talented young theoreticians was selected by Academicians Ya.B. Zel'dovich and A.D. Sakharov for work on the nuclear weapons program at VNIIEF. In 1963, he was awarded the Lenin Prize for the development of new principles and new approaches to nuclear and thermonuclear weapons design and controlled fusion; in 1964, he received the degree of Candidate of Science, and four years later, the degree of Doctor of Science. V.N. Mokhov was always inspired by challenging projects that required teamwork of theoreticians, designers, and experimentalists. His major scientific and practical results include: Development of the theory of turbulent mixing in layered structures at intense compression. The results obtained are relevant for studying the processes occurring in inertial confinement fusion (ICF) targets.; Ignition of thermonuclear fuel by its heating with fast compression, which was and continues to be very important for the development of a number of special-purpose nuclear charges and fusion targets.; Development of “clean” nuclear charges for peaceful applications (jointly with the team of colleagues).; The new approach to the controlled thermonuclear fusion - the MAGO (MAGnitnoye Obzhatiye, or magnetic compression) - was proposed and developed jointly with his team. V.N. Mokhov considered MAGO to be a system that now made it possible to achieve the scientific breakeven point for fusion without the large initial capital investment that is required by the two more conventional approaches, magnetic confinement fusion and ICF.; Investigation of physical properties of materials at high energy densities provided by explosive magnetic flux compression generators (EMG). Jointly with his team, V.N. Mokhov proposed and developed methods of this investigation, obtained novel results on dynamic strength of a number of materials (aluminum, copper, polyethylene). In 1998, he and some of his colleagues were awarded the RF Government Prize for the development of EMGs and their application for scientific investigations. V.N. Mokhov was one of the pioneers of scientific cooperation between US and Russian nuclear laboratories. This mutually beneficial cooperation between the two countries produced extremely interesting scientific results obtained during joint research activities, including more than 20 series of experiments, and published in more than 400 papers and presentations. Equally important is that he was a true friend of many US scientists, and this friendship between people from different countries and trust in each other made the world better. V.N. Mokhov was a very interesting person having his original opinion on nearly any issue - whether related to science, history or politics. Many of his ideas on these issues were reflected in his papers available to a broad public and in his book “Nuclear Weapons and Safe Stable World. These ideas were extremely up-to-date in due time, and they continue to be relevant these days.