Bob Nagler

Bio: Bob Nagler is an academic researcher from SLAC National Accelerator Laboratory. The author has contributed to research in topics: Laser & Free-electron laser. The author has an hindex of 35, co-authored 182 publications receiving 5551 citations. Previous affiliations of Bob Nagler include Dresden University of Technology & Vrije Universiteit Brussel.

GeV electron beams from a centimetre-scale accelerator

Abstract: Gigaelectron volt (GeV) electron accelerators are essential to synchrotron radiation facilities and free-electron lasers, and as modules for high-energy particle physics. Radiofrequency-based accelerators are limited to relatively low accelerating fields (10–50 MV m−1), requiring tens to hundreds of metres to reach the multi-GeV beam energies needed to drive radiation sources, and many kilometres to generate particle energies of interest to high-energy physics. Laser-wakefield accelerators1,2 produce electric fields of the order 10–100 GV m−1 enabling compact devices. Previously, the required laser intensity was not maintained over the distance needed to reach GeV energies, and hence acceleration was limited to the 100 MeV scale3,4,5. Contrary to predictions that petawatt-class lasers would be needed to reach GeV energies6,7, here we demonstrate production of a high-quality electron beam with 1 GeV energy by channelling a 40 TW peak-power laser pulse in a 3.3-cm-long gas-filled capillary discharge waveguide8,9.

Creation and diagnosis of a solid-density plasma with an X-ray free-electron laser

Abstract: Experimental study of the interactions between intense X-rays and solid matter illustrate the generation of a solid-density plasma governed by electron–ion collisions; these results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological samples, material science investigations, and the study of matter in extreme conditions. With the advent of free-electron lasers, the high intensities previously only achievable with optical lasers can be produced at X-ray wavelengths. This opens new opportunities for theory and experiment. Here, Vinko et al. report the first detailed study of intense X-ray radiation interacting with solid density matter, carried out on the Linac Coherent Light Source free-electron laser at the SLAC National Accelerator Facility in California. They observe the generation of a solid-density plasma and establish that collisions have a pivotal role. The results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological samples and materials science investigations. Matter with a high energy density (>105 joules per cm3) is prevalent throughout the Universe, being present in all types of stars1 and towards the centre of the giant planets2,3; it is also relevant for inertial confinement fusion4. Its thermodynamic and transport properties are challenging to measure, requiring the creation of sufficiently long-lived samples at homogeneous temperatures and densities5,6. With the advent of the Linac Coherent Light Source (LCLS) X-ray laser7, high-intensity radiation (>1017 watts per cm2, previously the domain of optical lasers) can be produced at X-ray wavelengths. The interaction of single atoms with such intense X-rays has recently been investigated8. An understanding of the contrasting case of intense X-ray interaction with dense systems is important from a fundamental viewpoint and for applications. Here we report the experimental creation of a solid-density plasma at temperatures in excess of 106 kelvin on inertial-confinement timescales using an X-ray free-electron laser. We discuss the pertinent physics of the intense X-ray–matter interactions, and illustrate the importance of electron–ion collisions. Detailed simulations of the interaction process conducted with a radiative-collisional code show good qualitative agreement with the experimental results. We obtain insights into the evolution of the charge state distribution of the system, the electron density and temperature, and the timescales of collisional processes. Our results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological systems, material science investigations, and the study of matter in extreme conditions.

Direct measurements of the ionization potential depression in a dense plasma.

Abstract: We have used the Linac Coherent Light Source to generate solid-density aluminum plasmas at temperatures of up to 180 eV By varying the photon energy of the x rays that both create and probe the plasma, and observing the $K\mathrm{\text{\ensuremath{-}}}\ensuremath{\alpha}$ fluorescence, we can directly measure the position of the $K$ edge of the highly charged ions within the system The results are found to disagree with the predictions of the extensively used Stewart-Pyatt model, but are consistent with the earlier model of Ecker and Kr\"oll, which predicts significantly greater depression of the ionization potential

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

Abstract: Warm dense matter (WDM), which falls in the category between plasmas and condensed matter, is expected to exist in planetary interiors. Now, researchers use an X-ray laser to observe the transition to WDM.

Turning solid aluminium transparent by intense soft X-ray photoionization

Abstract: The first experimental demonstration of saturable absorption in core-electron transitions in aluminium paves the way for investigating warm dense matter, which potentially has an important role in planetary science and the realization of inertial confinement fusion.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

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