Contrasting environmental effects of astronomically driven climate change on three Eocene hemipelagic successions from the Basque–Cantabrian Basin

Sedimentology Wiley 64:4 (2017) 960-986

Authors:

Naroa Martínez‐Braceras, Aitor Payros, Francesco Miniati, Javier Arostegi, Gloria Franceschetti

Optimization of plasma amplifiers

Physical Review E American Physical Society (2017)

Authors:

James D Sadler, Raoul MGM Trines, Max Tabak, Dan Haberberger, Dustin H Froula, Andrew S Davies, Sara Bucht, Luís O Silva, E Paulo Alves, Frederico Fiuza, Luke Ceurvorst, Naren Ratan, Muhammad F Kasim, Robert Bingham, Peter Norreys

Abstract:

Plasma amplifiers offer a route to side-step limitations on chirped pulse amplification and generate laser pulses at the power frontier. They compress long pulses by transferring energy to a shorter pulse via the Raman or Brillouin instabilities.We present an extensive kinetic numerical study of the three-dimensional parameter space for the Raman case. Further particle-in-cell simulations find the optimal seed pulse parameters for experimentally relevant constraints. The high-efficiency self-similar behavior is observed only for seeds shorter than the linear Raman growth time. A test case similar to an upcoming experiment at the Laboratory for Laser Energetics is found to maintain good transverse coherence and high-energy efficiency. Effective compression of a 10 kJ, nanosecond-long driver pulse is also demonstrated in a 15-cm-long amplifier.

Robustness of raman plasma amplifiers and their potential for attosecond pulse generation

High Energy Density Physics Elsevier 23 (2017) 212-216

Authors:

James D Sadler, Marcin Sliwa, Thomas Miller, Muhammad F Kasim, Naren Ratan, Luke Ceurvorst, Alex Savin, Ramy Aboushelbaya, Peter Norreys, Dan Haberberger, Andrew S Davies, Sara Bucht, Dustin H Froula, Jorge Vieira, Ricardo A Fonseca, Luís O Silva, Robert Bingham, Kevin Glize, Raoul MGM Trines

Abstract:

Raman back-scatter from an under-dense plasma can be used to compress laser pulses, as shown by several previous experiments in the optical regime. A short seed pulse counter-propagates with a longer pump pulse and energy is transferred to the shorter pulse via stimulated Raman scattering. The robustness of the scheme to non-ideal plasma density conditions is demonstrated through particle-in-cell simulations. The scale invariance of the scheme ensures that compression of XUV pulses from a free electron laser is also possible, as demonstrated by further simulations. The output is as short as 300 as, with energy typical of fourth generation sources.

Machine learning applied to proton radiography of high-energy-density plasmas

Physical Review E American Physical Society 95:4 (2017) 043305

Authors:

Nicholas FY Chen, Muhammad F Kasim, Luke Ceurvorst, Naren Ratan, James Sadler, Matthew C Levy, Raoul Trines, Robert Bingham, Peter Norreys

Abstract:

Proton radiography is a technique extensively used to resolve magnetic field structures in high-energy-density plasmas, revealing a whole variety of interesting phenomena such as magnetic reconnection and collisionless shocks found in astrophysical systems. Existing methods of analyzing proton radiographs give mostly qualitative results or specific quantitative parameters, such as magnetic field strength, and recent work showed that the line-integrated transverse magnetic field can be reconstructed in specific regimes where many simplifying assumptions were needed. Using artificial neural networks, we demonstrate for the first time 3D reconstruction of magnetic fields in the nonlinear regime, an improvement over existing methods, which reconstruct only in 2D and in the linear regime. A proof of concept is presented here, with mean reconstruction errors of less than 5% even after introducing noise. We demonstrate that over the long term, this approach is more computationally efficient compared to other techniques. We also highlight the need for proton tomography because (i) certain field structures cannot be reconstructed from a single radiograph and (ii) errors can be further reduced when reconstruction is performed on radiographs generated by proton beams fired in different directions.

Numerical modeling of laser-driven experiments aiming to demonstrate magnetic field amplification via turbulent dynamo

Physics of Plasmas AIP Publishing 24:4 (2017) 041404

Authors:

P Tzeferacos, A Rigby, A Bott, Anthony Bell, R Bingham, A Casner, F Cattaneo, EM Churazov, J Emig, N Flocke, F Fiuza, CB Forest, J Foster, C Graziani, J Katz, M Koenig, C-K Li, J Meinecke, R Petrasso, H-S Park, BA Remington, JS Ross, D Ryu, D Ryutov, K Weide

Abstract:

The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model behind cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo to the values observed. We have conceived experiments that aim to demonstrate and study the turbulent dynamo mechanism in the laboratory. Here, we describe the design of these experiments through simulation campaigns using FLASH, a highly capable radiation magnetohydrodynamics code that we have developed, and large-scale three-dimensional simulations on the Mira supercomputer at the Argonne National Laboratory. The simulation results indicate that the experimental platform may be capable of reaching a turbulent plasma state and determining the dynamo amplification. We validate and compare our numerical results with a small subset of experimental data using synthetic diagnostics.