Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session CO7: Relativistic Laser Plasma Interaction and Particles (ions, electrons, positrons, neutrons) I |
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Chair: Marija Vranic, Instituto Superior Técnico, Universidade de Lisboa Room: OCC B117-119 |
Monday, November 5, 2018 2:00PM - 2:12PM |
CO7.00001: Dynamics of laser-driven positron beam focusing Joohwan Kim, Hui Chen, Anthony J. Link, Shaun Kerr, Gerald J Williams, Farhat N Beg Positron beams driven by direct laser plasma interaction are appealing for their possibility to provide astrophysics relevant conditions. To achieve required conditions, production of high-density positron jets is necessary. Here, we report dynamics of laser-driven positron beam focusing, resulting in high positron beam density by using a spherically curved target surface. Numerical modeling using the hybrid-PIC code shows positron acceleration by electric sheath field on the target surface at target normal direction resulting in ~x5 increase in local positron density for the curved target compared to the flat target case. It is also seen that additional structures attached on a target effectively change positron dynamics giving a further focusing effect. Detailed simulation results including field evolution and beam characteristics will be presented. |
Monday, November 5, 2018 2:12PM - 2:24PM |
CO7.00002: Radiation-dominated particle and plasma dynamics Arkady Gonoskov, Mattias Marklund The prospects of using the upcoming high-intensity laser facilities has stimulated the interest in understanding the effects induced by intense radiation losses. This can guide the development of new experimental efforts, such as the creation of new gamma-ray sources for nuclear and quark-nuclear physics, as well as for mimicking and understanding astrophysical scenarios. We describe a universal theoretical approach for understanding and analyzing the dynamics of particles and plasmas in strong electromagnetic field of arbitrary configuration. We find that the intense drain of kinetic energy by radiation losses (in either classical or quantum form) leads to the tendency of particles to approach a direction that yields zero lateral acceleration (relative to their direction of motion). By deriving an explicit expression for such radiation free direction (RFD), we develop a closed description of both particle and plasma dynamics in this regime: at each point of space, the particles mainly move and form currents along the local RFD, while the deviation of their motion from the RFD can be calculated in order to account for their incoherent emission. |
Monday, November 5, 2018 2:24PM - 2:36PM |
CO7.00003: Integrated probing of sheath field evolution using laser-generated positrons Shaun Kerr, Anthony J. Link, Gerald J Williams, Jaebum Park, Hui Chen, Robert Fedosejevs, Joohwan Kim Positrons generated by ultraintense lasers are rapidly accelerated by TNSA fields, and may offer an integrated, temporally resolved probe of these fields for multi-picosecond, kilojoule class lasers such as NIF ARC. The use of positron spectral information as a diagnostic of target conditions is evaluated using 2D LSP PIC simulations, which are compared with experimental results collected at OMEGA EP [1]. A capacitor model [2] is used to predict the charging of the target and the energies of the positron spectral features. The factors that influence the target fields over time and corresponding positron acceleration are discussed. [1] Chen et al., PoP 22, 056705 (2015) [2] Link et al., PoP 18, 053107 (2011) |
Monday, November 5, 2018 2:36PM - 2:48PM |
CO7.00004: Gamma-ray generation and pair production from extreme laser-driven magnetic fields Oliver Jansen, Tao Wang, David Stark, Zheng Gong, Toma Toncian, Alexey Arefiev The ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable[1]. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dense beams. Presented simulations using a novel simulation code show that more than 103 pairs can be produced in such a setup, and the directionality of the positrons can be controlled by the angle of incidence between the beams. |
Monday, November 5, 2018 2:48PM - 3:00PM |
CO7.00005: Benchmarking semiclassical approaches to strong-field QED Tom Blackburn, Daniel Seipt, Stepan Bulanov, Mattias Marklund The recoil exerted due to photon emission plays a key role in particle dynamics in ultrastrong electromagnetic fields. In laser-matter interactions beyond the current intensity frontier, or in astrophysical environments such as neutron magnetospheres, individual photons of the emitted radiation have energies comparable to that of the electron, making it necessary to take quantum effects into account. However, calculating the scattering matrix element directly from strong-field QED is not possible for many scenarios of interest due to high multiplicity and the complex structure of the electromagnetic fields. Numerical modelling of these interactions is therefore based upon a semiclassical approach, in which probabilistic emission events are coupled to classical electrodynamics using rates calculated in the locally constant field approximation. We discuss recent work in which we provide comprehensive benchmarking of this approach against exact QED results. |
Monday, November 5, 2018 3:00PM - 3:12PM |
CO7.00006: Onset of electron-positron pair cascades in the collision of tightly focused 10 GeV-class lepton beams Dario Del Sorbo, Fabrizio Del Gaudio, Thomas Grismayer, Eduardo Alves, Vitaly Yakimenko, Sebastian Meuren, Luis O Silva, Warren B Mori, Frederico Fiuza Electron-positron pair cascades develop in extreme astrophysical environments, such as pulsar magnetospheres, and are of fundamental interest in strong-field quantum electrodynamics. Recently, there has been a significant effort to infer the conditions for the onset of pair cascades in the laboratory, using ultra-intense laser fields, such as those soon to be available at multi-petawatt laser facilities. Here, we explore the possibility of studying pair cascades in the collision of tightly focused lepton beams. When tightly compressed, these charged particle beams can possess electric fields with strengths comparable to multi-PW laser beams. As highly relativistic particles experience these extreme fields from the opposite beam they can produce copious amounts of high-energy radiation, which will in turn produce pairs (T. Grismayer et al, this conference), and give rise to a cascade. Expanding the work for low disruptions regimes (F. Del Gaudio et al., submitted), we discuss the optimal conditions to study this in the laboratory and the corresponding observables. |
Monday, November 5, 2018 3:12PM - 3:24PM |
CO7.00007: From classical to quantum radiation reaction effects in ultra high intensity laser plasmainteraction Caterina Riconda, Fabien Niel, François Amiranoff, Mickael Grech Radiation reaction (RR) in the interaction of ultra-relativistic electrons with a strong external
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Monday, November 5, 2018 3:24PM - 3:36PM |
CO7.00008: Plasma simulations using real-time lattice scalar-QED Yuan Shi, Jianyuan Xiao, Hong Qin, Nathaniel J Fisch When dense plasmas are exposed to intense fields, intrinsically relativistic-quantum effects such as pair production can happen. To faithfully capture such phenomena when scales are not well separated, a unique tool is provided by real-time lattice quantum electrodynamics (QED). As a toy model, we consider scalar-QED, which describes bosonic plasmas. This model can be solved, in the classical-statistic regime, by advancing an ensemble of statistically equivalent initial conditions in time using the Klein-Gordon-Maxwell (KGM) equations, for which we have developed a variational algorithm. To demonstrate the capability of our numerical scheme, we apply it to two example problems. The first example is the propagation of linear waves, whose numerical spectrum recovers the analytic wave dispersion relations. The second example is pair production when intense X-ray lasers interact with a dense plasma target, whereby we demonstrate natural transition from wakefield acceleration to pair production when the laser amplitude exceeds the Schwinger threshold. |
Monday, November 5, 2018 3:36PM - 3:48PM |
CO7.00009: Radiation Dominated Electromagnetic Shield Stepan Bulanov, James Kevin Koga, Kinimori Kondo, Timur Esirkepov, Masaki Kando, Arkady Gonoskov, Joel Magnusson, Jianhui Bin, Qing Ji, Sven Steinke, Thomas Schenkel, Carl B Schroeder, Eric Esarey, Wim Pieter Leemans, Sergei Bulanov, Georg Korn We analyze the radiating electron interaction with oscillating electric and magnetic field configurations, which represent three-dimensional standing electromagnetic waves having various electromagnetic field polarizations. During collision of a high energy beam of ultra-relativistic electrons with a high amplitude electromagnetic field, when the radiation friction force effects are dominant, asymptotically becomes trapped in the regions of the local maximum of the electric field due to nonlinear dependence of the radiation friction force on the driver electromagnetic field. We discuss possible experimental implementation of this field configuration. |
Monday, November 5, 2018 3:48PM - 4:00PM |
CO7.00010: Positron generation and acceleration by injecting two ultra-relativistic intense electron beams upon high-Z target Hiroki Fujii, Weiming An, Kenneth A Marsh, Chan Joshi We numerically study the plasma acceleration of trailing positron bunch as a result of injecting two ultra-relativistic incident electron bunches upon high-Z target [X. Wang, et. al., PRL 101, 124801 (2008)]. The experiment is capable at a new 10 GeV electron beam facility, Facilities for Accelerator Science and Experimental Test (FACET) II, which is under construction for the ultra-relativistic beam-driven plasma wakefield accelerator. We demonstrate the drive positrons and the trailing electrons experience defocusing force due to the excitation of nonlinear wake inside plasma, while trailing positrons are trapped and accelerated when two bunches are properly spaced. The effects of beam parameters and geometries are explored with the aim of optimizing the positron acceleration. We support our findings with the 3D Monte Carlo simulation EGS5 and the 3D particle-in-cell code QuickPIC [W. An et al., JCP 250, 165 (2013)]. Since the beam density at FACET II reaches the order of ~1020 cm−3, we also discuss the effect of strong magnetic field generation inside the high-Z target which enhances the gamma-ray flux and the number of positrons beyond the expectation of EGS5 result. |
Monday, November 5, 2018 4:00PM - 4:12PM |
CO7.00011: New routes to high-energy photon generation in laser-matter interactions Mattias Marklund Over the last decade, rigorous efforts in the development of particle-in-cell (PIC) schemes with corrections from quantum electrodynamics (QED) have resulted in many new and exciting predictions of high-energy photon generation. Here, we will present results based on state-of-the-art QED-PIC and analytical calculations on the generation of high-energy photons from laser-plasma and laser-beam systems. Closely connected to the emission of high-energy photons are electromagnetic cascades of electron-positron pairs. In the cascade process, radiation reaction and rapid electron-positron plasma production seemingly restrict the efficient production of photons to sub-GeV energies. Here, we show how the interplay between the pair cascade and radiation reaction effects results in the possibility to emit high-energy photons. The possibility to use tailored laser fields as well as particular particle sources promises not only the generation of high-energy photons, but also of controlled pair production at very high densities. Such matter—anti-matter/radiation systems could be of importance for laboratory astrophysics. |
Monday, November 5, 2018 4:12PM - 4:24PM |
CO7.00012: Theory of Radiative Electron Polarization in Strong Laser Fields Daniel Seipt, Alexander GR Thomas, Christopher P Ridgers, Dario Del Sorbo Recent high-intensity laser-plasma experiments provided evidence for quantum radiation reaction effects due to hard photon emission. In this talk I will focus on the influence of electron spin polarization on the non-linear Compton photon emission, and radiative spin-polarization as a manifestation of quantum radiation reaction affecting the spin-dynamics of electrons. We recently showed that a build-up of spin-polarization of electrons---analogous to the Sokolov-Ternov effect---is possible for electrons in counter-propagating laser pulses with intensities exceeding 5 × 10^22 W/cm^2 on femtosecond timescales. I will present a density matrix approach for describing the radiative beam polarization in strong electromagnetic fields. The local constant crossed field approximation (LCFA) for the polarization density matrix is derived, which is a generalization of the well known LCFA scattering rates. We find spin-dependent expressions that may be included in electromagnetic charged-particle simulation codes, such as particle-in-cell plasma simulation codes, using Monte-Carlo modules. The validity of the LCFA is confirmed by explicit comparison with an exact QED calculation of electron polarization in an ultrashort laser pulse. |
Monday, November 5, 2018 4:24PM - 4:36PM |
CO7.00013: Interaction of Electron Beams with Optimally Focused Laser Radiation in the QED Regime Joel Magnusson, Arkady Gonoskov, Mattias Marklund, Timur Esirkepov, James Kevin Koga, Kinimori Kondo, Masaki Kando, Sergei Bulanov, Georg Korn, Stepan Bulanov Upcoming large-scale high-intensity laser facilities are about to open the opportunity to reach intensities sufficient for entering QED regimes of laser-matter interaction. These open up opportunities for producing gamma ray beams in the new range of parameters that have a potential to serve for fundamental studies in nuclear and quark-nuclear physics. In our study we analyse the capabilities of reaching the highest possible energies of photons in combination with high fluxes using the concept of colliding beams of high-energy electrons with high-intensity multiple-colliding laser pulses (MCLP). We present the analysis of several potential configurations and compare them in the context of the outlined problem. Achievable characteristics of high-energy photon beams are obtained for parameters accessible at current and upcoming laser facilities. |
Monday, November 5, 2018 4:36PM - 4:48PM |
CO7.00014: Creating dense gamma-rays and electron-positron pairs with 10^21 W.cm^-2 short-pulse laser Edison Liang On behalf of the Rice-UTA-MDA Positron-Gamma-Ray Collaboration*, we report the latest results of the 2016-2018 dense gamma-ray and positron experiments. Using the Texas Petawatt Laser (TPW) to irradiate thick Au and Pt targets at intensities ≥10^21 W/cm^2 , we have created high-density (10^15/cm^3), short-pulse (100 fs) e+e- pair and gamma-ray jets with in-situ physical parameters comparable to those postulated for cosmic gamma-ray bursts. For large cm-sized targets, we discover that hot electron emission is suppressed in a cone between the target normal and laser forward directions, while the positron emission is not suppressed. This leads to the creation of angle-selectable positron-dominated jets, with many applications to fundamental physics and astrophysics. We will also present the gamma-ray data from a new type of gamma-ray spectrometer, and discuss potential future applications of ultra-intense multi-MeV gamma-ray beams. * E. Liang, W. Lo, Y. Lu, K. Yao, A. Henderson, E. Marchenka, F. Fasanelli, A. Zhang, W. Fu, P. Chaguine, Rice University; H. Hassan, A. Dashko, G. Glen, G. Tiwari, H. Quevedo, G. Dyer, M. Donovan, T. Ditmire, UT Austin; G. Wong, Y. Zhang, MD Anderson Cancer Center. |
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