Machine learning controlled laser wakefield acceleration simulations

One of the most promising technologies to form the next generation of compact particle accelerators is plasma acceleration. Plasmas have the ability to sustain waves with electric fields that can be three orders of magnitude higher than those in radio frequency (RF) cavities.The ultimate goal of plasma-based acceleration is to produce relativistic, high quality electron and positron bunches for scientific and societal applications. The recent progress has been tremendous but improving beam quality still remains as a grand-challenge in the field.The fundamental aspects and properties of these accelerators are accessible through simplified analytical models, but the self-consistent dynamics of the laser in the plasma can only be captured by numerical simulations. Search for optimised parameters to improve beam quality can be based on systematic parameter scans. However, because numerical calculations can be very computationally intensive, it is important to investigate more efficient techniques to scan over the entire parameter range currently available. In this work, we propose a machine learning approach to optimize this search based on genetic algorithms.Recent experiments have employed genetic algorithms to control plasma based accelerators[1]. Here, instead, we will employ this technique to control the outputs and optimise plasma-based accelerators in particle-in-cell (PIC) simulations. We implemented a genetic algorithm in ZPIC, a fully relativistic PIC educational code[2]. The genetic algorithm is fully automated: it receives an initial set of input parameters, launches several simulations in parallel using MPI, and ends automatically once given convergence criteria are reached. The algorithm can thus take full advantage of large-scale super-computers. We present results from 1D simulations.We focus on plasmas with non-uniform density and lasers with variable longitudinal envelope profiles.info:eu-repo/semantics/publishedVersio

Analytic pulse technique for computational electromagnetics

Numerical modeling of electromagnetic waves is an important tool for understanding the interaction of light and matter, and lies at the core of computational electromagnetics. Traditional approaches to injecting and evolving electromagnetic waves, however, can be prohibitively expensive and complex for emerging problems of interest and can restrict the comparisons that can be made between simulation and theory. As an alternative, we demonstrate that electromagnetic waves can be incorporated analytically by decomposing the physics equations into analytic and computational parts. In particle-in-cell simulation of laser--plasma interaction, for example, treating the laser pulse analytically enables direct examination of the validity of approximate solutions to Maxwell's equations including Laguerre--Gaussian beams, allows lower-dimensional simulations to capture 3-D--like focusing, and facilitates the modeling of novel space--time structured laser pulses such as the flying focus. The flexibility and new routes to computational savings introduced by this analytic pulse technique are expected to enable new simulation directions and significantly reduce computational cost in existing areas.Comment: 26 pages, 9 figure

Coherence and superradiance from a plasma-based quasiparticle accelerator

Coherent light sources, such as free electron lasers, provide bright beams for biology, chemistry, physics, and advanced technological applications. Increasing the brightness of these sources requires progressively larger devices, with the largest being several km long (e.g., LCLS). Can we reverse this trend, and bring these sources to the many thousands of labs spanning universities, hospitals, and industry? Here we address this long-standing question by rethinking basic principles of radiation physics. At the core of our work is the introduction of quasi-particle-based light sources that rely on the collective and macroscopic motion of an ensemble of light-emitting charges to evolve and radiate in ways that would be unphysical when considering single charges. The underlying concept allows for temporal coherence and superradiance in fundamentally new configurations, providing radiation with clear experimental signatures and revolutionary properties. The underlying concept is illustrated with plasma accelerators but extends well beyond this case, such as to nonlinear optical configurations. The simplicity of the quasi-particle approach makes it suitable for experimental demonstrations at existing laser and accelerator facilities.Comment: 15 pages, 4 figure

Nonlinear Thomson scattering with ponderomotive control

In nonlinear Thomson scattering, a relativistic electron reflects and re-radiates the photons of a laser pulse, converting optical light to x rays or beyond. While this extreme frequency conversion offers a promising source for probing high-energy-density materials and driving uncharted regimes of nonlinear quantum electrodynamics, conventional nonlinear Thomson scattering has inherent tradeoffs in its scaling with laser intensity. Here we discover that the ponderomotive control afforded by spatiotemporal pulse shaping enables novel regimes of nonlinear Thomson scattering that substantially enhance the scaling of the radiated power, emission angle, and frequency with laser intensity. By appropriately setting the velocity of the intensity peak, a spatiotemporally shaped pulse can increase the power radiated by orders of magnitude. The enhanced scaling with laser intensity allows for operation at significantly lower electron energies and can eliminate the need for a high-energy electron accelerator

Exact solutions for the electromagnetic fields of a flying focus

The intensity peak of a "flying focus" travels at a programmable velocity over many Rayleigh ranges while maintaining a near-constant profile. Assessing the extent to which these features can enhance laser-based applications requires an accurate description of the electromagnetic fields. Here we present exact analytical solutions to Maxwell's equations for the electromagnetic fields of a constant-velocity flying focus, generalized for arbitrary polarization and orbital angular momentum. The approach combines the complex source-point method, which transforms multipole solutions into beam-like solutions, with the Lorentz invariance of Maxwell's equations. Propagating the fields backward in space reveals the space-time profile that an optical assembly must produce to realize these fields in the laboratory. Comparisons with simpler paraxial solutions provide conditions for their reliable use when modeling a flying focus

Coherence and superradiance from a plasma-based quasiparticle accelerator

International audienceCoherent light sources, such as free electron lasers, provide bright beams for biology, chemistry, physics, and advanced technological applications. Increasing the brightness of these sources requires progressively larger devices, with the largest being several km long (e.g., LCLS). Can we reverse this trend, and bring these sources to the many thousands of labs spanning universities, hospitals, and industry? Here we address this long-standing question by rethinking basic principles of radiation physics. At the core of our work is the introduction of quasi-particle-based light sources that rely on the collective and macroscopic motion of an ensemble of light-emitting charges to evolve and radiate in ways that would be unphysical when considering single charges. The underlying concept allows for temporal coherence and superradiance in fundamentally new configurations, providing radiation with clear experimental signatures and revolutionary properties. The underlying concept is illustrated with plasma accelerators but extends well beyond this case, such as to nonlinear optical configurations. The simplicity of the quasi-particle approach makes it suitable for experimental demonstrations at existing laser and accelerator facilities

The relationship between visual acuity impairment and studying medicine among second year medical students of DLSHSI College of Medicine A.Y. 2016-2017

The study used a case-control type of research design, wherein the baseline data that was used were the results of the physical examination specially the visual acuity part during the first year of medical school. Non-probability purposive sampling was utilized. All of the second-year medical students were asked permission via consent form with regard to reviewing their chart. Based on the McNemar test results, it can be said that there was an association between studying medicine and the development of visual acuity impairment. Furthermore, the odds ratio of 2.16 indicated that there was a causative relationship between visual acuity impairment and studying medicine