Talbot-Lau x-ray interferometry for high energy density plasma diagnostic

Phase-contrast x-ray imaging techniques can detect density gradients in low-Z matter with the sensitivity and spatial resolution necessary to characterize High Energy Density Laboratory Plasma (HEDLP) experiments. The Talbot-Lau interferometer measures x-ray beam angular deviations due to refraction index gradients along its path, thus making it an attractive plasma diagnostic. The Talbot-Lau interferometer can simultaneously provide x-ray attenuation, refraction, and scatter images which may offer a simple diagnostic for micro instabilities. We extend the Talbot-Lau method used for medical applications to lower x-ray energies, high magnification and high spatial resolution HEDLP experiments require. We study and develop single image based phase-retrieval techniques. The experimental and simulated results obtained show a clear advantage of the Talbot-Lau Moiré technique over the attenuation and propagation methods. The Moiré technique can detect both sharp and smooth density gradients, using extended, polychromatic, incoherent, line and continuum x-ray sources, thus allowing for less demanding backlighters than those typically used in HEDLP radiography.

X-ray phase-contrast radiography could better characterize highly localized density gradients expected in High Energy Density (HED) plasma experiments than conventional attenuation radiography. In particular, the Talbot-Lau (TL) grating interferometer, which works with extended and polychromatic x-ray sources, is a potentially attractive HED diagnostic due to its high sensitivity. For HED characterization the TL setup and imaging techniques must be changed from the recently studied medical system. The object magnification must be increased greatly in order to resolve μm scale gradients while the Talbot magnification must be increased in order to keep the gratings away from the plasma. Additionally, techniques for retrieving the density profile from a single plasma image must be developed. We thus study the performance of high magnification TL interferometers, in conjunction with Moiré fringe deflectometry for single image phase retrieval. The results show a very good interferometer contrast (≤30%) at high magnification. The Moiré technique enables measuring both sharp and mild density gradients with good accuracy and spatial resolution. Both the laboratory and simulation studies indicate that the TL based Moiré deflectometry is more sensitive than the propagation phase-contrast method when utilizing an extended x-ray source (∼80 μm). In HED experiments this would allow for less demanding X-ray backlighters than those used at present.

Propagation of charged particle beams in background plasma as a method of space charge neutralization has been shown to achieve a high degree of charge and current neutralization and therefore enables nearly ballistic propagation and focusing of charged particle beams. Correspondingly, the use of plasmas for propagation of charged particle beams has important applications for transport and focusing of intense particle beams in inertial fusion and high energy density laboratory plasma physics. However, the streaming of beam ions through a background plasma can lead to the development of two-stream instability between the beam ions and the plasma electrons. The beam electric and magnetic fields enhanced by the two-stream instability can lead to defocusing of the ion beam. Using particle-in-cell simulations, we study the scaling of the instability-driven self-electromagnetic fields and consequent defocusing forces with the background plasma density and beam ion mass. We identify plasma parameters where the defocusing forces can be reduced.

Atomic physics and ionization balance of high-Z Ions: Critical ingredients for characterizing and understanding high-temperature plasmas

In February 2015, the Department of Energy, Office of Science, Fusion Energy Sciences (FES)” announced the formation of four technical workshops “to seek community engagement and input for future program planning activities.” Three of these workshops focused on the science and technical challenges we must address to meet the emerging needs of ITER and to allow exploration of fusion burning plasma physics in the laboratory. This report represents the work of the fourth workshop, which focused on the broader scientific opportunities at the frontiers of plasma science. The primary charge to the Panel authoring this report was “to ‘identify’ compelling scientific challenges at the frontiers of plasma physics” and “to ‘identify’ research tools and capabilities to address these challenges in the next decade.” This report aims to inform the newly constituted FES Program in Frontiers of Plasma Science on science opportunities and strategy moving forward. This program was created in FY2015 by combining topics from general plasma science, high energy density laboratory plasmas, and exploratory magnetized plasma into a single program area. The Executive Summary, chapter introductions and sidebars to the chapter are intended to provide more general overviews of the findings of the panel. The chapters provide more details following these themes.

Magnetic field and electron density diagnostics are critical tools in the characterization of high energy density laboratory plasmas. These plasma environments are complex and the magnetic fields and electron densities often exhibit significant spatial and temporal variation leading to significant challenges in these measurements. Even the most promising technique, Zeeman splitting, faces challenges under plasma conditions where broadening due to high density and temperature is greater than the Zeeman splitting. Here we propose and describe a diagnostic based on Zeeman broadening. The Zeeman broadening diagnostic relies on measuring the widths of multiplet components simultaneously. The method does not depend on resolved lines, but rather on measuring the difference in the widths of multiplet lines. Experiments were performed at the University of Nevada, Reno, Nevada Terawatt Facility (NTF). The Zeeman broadening diagnostic gathered visible broadened multiplet spectra from laser produced plasmas, and plasmas generated from wire-arrays driven by the Zebra z-pinch pulsed power apparatus. The laser produced plasma, created by the Leopard pulsed laser (I>1014 W/cm2), evolved in an external magnetic field (B<40T) generated by current driven through a solid electrode by the Zebra current pulse. For laser produced plasmas, observation of the magnetic field radial profile showed that the external field completely diffuses into the plasma after approximately 100 ns. Further, as the plasma continues to evolve, the field profiles within the plasma develop modulations that do not map the external field profile. For the wire array experiments, radial electron density, and magnetic field, profiles were measured. Here the Zeeman splitting was not resolved and the magnetic fields were determined from the difference between the widths of the multiplet line profiles. Thus, it has been demonstrated that Zeeman broadening may be used as a magnetic field diagnostic.

Since the 1950s, scientists and engineers in the U.S. and around the world have worked hard to make an elusive goal to be achieved on Earth: harnessing the reaction that fuels the stars, namely fusion. Practical fusion would be a source of energy that is unlimited, safe, environmentally benign, available to all nations and not dependent on climate or the whims of the weather. Significant resources, most notably from the U.S. Department of Energy (DOE) Office of Fusion Energy Sciences (FES), have been devoted to pursuing that dream, and significant progress is being made in turning it into a reality. However, that is only part of the story. The process of creating a fusion-based energy supply on Earth has led to technological and scientific achievements of far-reaching impact that touch every aspect of our lives. Those largely unanticipated advances, spanning a wide variety of fields in science and technology, are the focus of this report. There are many synergies between research in plasma physics (the study of charged particles and fluids interacting with self-consistent electric and magnetic fields), high-energy physics, and condensed matter physics dating back many decades. For instance, the formulation of a mathematical theory of solitons, solitary waves which are seen in everything from plasmas to water waves to Bose-Einstein Condensates, has led to an equal span of applications, including the fields of optics, fluid mechanics and biophysics. Another example, the development of a precise criterion for transition to chaos in Hamiltonian systems, has offered insights into a range of phenomena including planetary orbits, two-person games and changes in the weather. Seven distinct areas of fusion energy sciences were identified and reviewed which have had a recent impact on fields of science, technology and engineering not directly associated with fusion energy: Basic plasma science; Low temperature plasmas; Space and astrophysical plasmas; High energy density laboratory plasmas and inertial fusion energy; Particle accelerator technology; Fusion nuclear science; and Magnetically confined plasmas. Individual sections within the report summarize applications associated with each of these areas. These sections were also informed by a survey that went out to the community, and the subcommittee wishes to thank those who responded, as well as to the national labs and universities that contributed photographs.

The highly localized density gradients expected in High Energy Density (HED) plasma experiments can be characterized by x-ray phase-contrast imaging in addition to conventional attenuation radiography. Moiré deflectometry using the Talbot-Lau grating interferometer setup is an attractive HED diagnostic due to its high sensitivity to refraction induced phase shifts. We report on the adaptation of such a system for operation in the sub-10 keV range by using a combination of free standing and ultrathin Talbot gratings. This new x-ray energy explored matches well the current x-ray backlighters used for HED experiments, while also enhancing phase effects at lower electron densities. We studied the performance of the high magnification, low energy Talbot-Lau interferometer, for single image phase retrieval using Moiré fringe deflectometry. Our laboratory and simulation studies indicate that such a device is able to retrieve object electron densities from phase shift measurements. Using laboratory x-ray sources from 7 to 15 μm size we obtained accurate simultaneous measurements of refraction and attenuation for both sharp and mild electron density gradients.

Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of a higher volumetric energy density as well as gravimetric energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to cathode material’s much lower energy density compared to anode material. In this regard, Li-rich material (Li2MnO3-LiMO2, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoO2 is the unique next generation cathode material to solve the problem of cathode material’s low energy density. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF3 coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, achieving the high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. In general, Li-rich material’s reversible capacity is related with its particle size since the Li2MnO3 phase in large Li-rich material, which is a major component to realize high energy density, is not fully activated in low voltage range below 4.6 V. For this reason, many previous papers reported their results with only small primary particle size below 100nm. The high surface area induced by the small particle size increases side reactions with electrolyte resulting poor long-term cycle life as well as lowers the volumetric energy density. Note that Li-rich material’s deteriorations are generated from its surface and continue to affect its cycling capability and the deteriorations can be divided into two mechanisms: one is side reactions with electrolyte, and another is the phase collapse. The side reactions with electrolyte at its high working voltage yield active material attack speiceses such as HF and electrolyte exhaustion causing Li-rich material’s fast discharge capacity decay during cycles. Furthurmore, it is hardly show long-term cycle life with over 200 cycles since the phase transition from layered structure to spinel-like and NiO rock salt is generated on the surface of active material, and followed by expention of this transition into the bulk. For instance, AlF3 coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, although it showed good rate and cycle capability within 100 cycles. Hence, new active material design, rather than simple surface modification methods such as coating or doping, is required to solve above previous limits.The new material design needs to start with a simple question: how to minimize the damages of surface deteriorations such as side reasction with electrolyte and phase trasnsition on bulk material and maximize volumetric energy density. The most effective solution for the question is increasing the primary particle size with the stable activation method, since the volumetric energy density of cathode material is maximized from synthesis of micron secondary particles consisted of primary particles by using co-precipitation method in industry. Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large flake shaped primary particle (hundred nanometers x mictrometers) with a novel activation method using simple chemical treatment to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interstingly, the chemical approach activated only surface Li2MnO3 phase of large primary particle and the very surface activation effectively overcame the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with extremely high cycle retention during 400 cycles and high volumetric energy density ever reported before.

Talbot-Lau X-ray Deflectometry (TXD) has been developed as an electron density diagnostic for High Energy Density (HED) plasmas. The diagnostic delivers refraction, attenuation, elemental composition, and scatter information from a single-shot Moire image. A Talbot-Lau interferometer was benchmarked using laser-target and X-pinch x-ray backlighters. Grating survival and electron density mapping were demonstrated for: a) 25–60 J, 8–30 ps laser pulses using copper targets and b) X-pinches driven by a ~350kA/350ns generator. X -ray backlighter quality was assessed in order to optimize areal electron density gradient retrieval and electron density mapping. TXD enabled accurate areal electron density detection with high contrast (>25%) and spatial resolution of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 50\mu \mathrm{m}$</tex> in the high-power laser experiments, while a higher spatial resolution <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&lt; 27\mu \mathrm{m}$</tex> and lower contrast (<15%) were found in pulsed power experiments, thus demonstrating the potential of TXD as an electron density diagnostic for HED plasmas.

An important challenge in real-world biomedical applications of x-ray phase contrast imaging (XPCI) techniques is the efficient use of the photon flux generated by an incoherent and polychromatic x-ray source. This efficiency can directly influence dose and exposure time and ideally should not affect the superior contrast and sensitivity of XPCI. In this paper, we present a quantitative evaluation of the photon detection efficiency of two laboratory-based XPCI methods, grating interferometry (GI) and coded-aperture (CA). We adopt a Monte Carlo approach to simulate existing prototypes of those systems, tailored for mammography applications. Our simulations were validated by means of a simple experiment performed on a CA XPCI system. Our results show that the fraction of detected photons in the standard energy range of mammography are about 1.4% and 10% for the GI and CA techniques, respectively. The simulations indicate that the design of the optical components plays an important role in the higher efficiency of CA compared to the GI method. It is shown that the use of lower absorbing materials as the substrates for GI gratings can improve its flux efficiency by up to four times. Along similar lines, we also show that an optimized and compact configuration of GI could lead to a 3.5 times higher fraction of detected counts compared to a standard and non-optimised GI implementation.

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

Novel Na0.5Bi0.5TiO3 based, lead-free energy storage ceramics with high power and energy density and excellent high-temperature stability

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

Summary form only given. The x-pinch has proven to be a valuable continuum and line radiation source in high energy density (HED) plasma diagnostics such as x-ray absorption spectroscopy1 and monochromatic backlight imaging2. Landen et al.3 have shown laser-produced plasma x-ray sources can be successfully used to probe the high densities (ne > 1021 cm−3) encountered in many HED plasmas of interest by way of x-ray Thomson scattering, which can yield information on plasma temperature, density and charge state in the noncollective and collective scattering regimes. We attempt to determine if line radiation from certain materials in a standard/hybrid X-pinch configuration can meet the stringent probe radiation source requirements for x-ray Thomson scattering experiments4, i.e. photon count (minimum 1012 photons into the scattering volume), bandwidth (ΔE/E ≈ 0.01 for noncollective scattering, ΔE/E ≈ 0.002 for collective scattering) and sufficient separation from other characteristic line structures. Previous experiments have shown that the K-line radiation output from an X-pinch can reach upwards of 30J with almost 1J going into a single line in certain materials. A lower limit estimate of 10mJ into an intense and narrow K-shell line would yield roughly 1014 photons into 4π sr, which would translate to about 1012 photons into a scattering volume with a reasonable solid angle of 0.1 sr. Experimentally and computationally determined photon counts and time-integrated spectra obtained for the different materials studied are presented.