arXiv subjects

Ricardo Fonseca

Publications and source records attributed to Ricardo Fonseca.

10 recordsLinked to original sources

arXiv2026

The 2026 Algorithmic Information Theory Data Compression Challenge

Lossless data compression remains central to computer science, with direct impact on storage, communication bandwidth, computational cost, and energy consumption. It is also closely related to Algorithmic Information Theory, where compressibility provides an operational measure of structure and non-randomness. This paper presents the 2026 Algorithmic Information Theory Data Compression Challenge, a benchmark for evaluating general-purpose lossless compressors under realistic constraints. Submissions were encouraged to use arithmetic or range coding, limited to at most 8 GB of memory, and required to include a decompressor no larger than 1 MB. The benchmark comprised sixteen heterogeneous files, split into public training and hidden testing datasets. In total, 117 valid submitted compressors were evaluated alongside established reference compressors using compression ratio, compression and decompression time, Weissman score, and Pareto-frontier analysis. The results show that performance depends strongly on the optimization criterion: fast compressors achieved the best speed-oriented scores, whereas modelling-intensive compressors produced smaller outputs at higher computational cost. A Normalized Compression Distance analysis further revealed clusters of related submissions and distinguished incremental variants from more independent implementations. Selected submissions were described for their methodological novelty or competitive performance and further tested on four large external datasets, where several achieved competitive or superior results relative to established compressors. Overall, the challenge confirms the importance of probabilistic modelling, hidden testing, and external datasets for assessing compression performance and generalization. Benchmark resources, leaderboard data, binaries, and selected source code are publicly available at https://aitdcc.github.io.

cs.IT↗

arXiv2026

A Deterministic Ionization Algorithm for the OSIRIS Particle-in-Cell Framework

Ionization is critical in the formation and evolution of plasma dynamics; collisional ionization, in particular, is an often overlooked source of electrons when dealing with laser-plasma interactions. Ionization plays a crucial role in understanding the complex plasma kinetics, ranging from cold and sparse astrophysical settings to hot and dense fusion systems. In this paper, we describe the underlying theory for and development, validation, and verification of an extension to the standard particle-in-cell method to include a deterministic algorithm for collisional ionization physics. This algorithm offers improved accuracy, achieving up to two orders of magnitude decrease in the error of the ionization rate calculations, scales linearly in execution time with the number of macro-particles per cell, has been tested for physical correctness and benchmarked against several codes.

physics.plasm-ph↗

arXiv2025

Plasma Accelerator For Decaying Particles

We introduce a plasma wakefield acceleration scheme capable of boosting initially subrelativistic particles to relativistic velocities within millimeter-scale distances. A subluminal light pulse drives a wake whose velocity is continuously matched to the beam speed through a tailored plasma density, thereby extending the dephasing length. We develop a theoretical model that is generalizable across particle mass, initial velocity, and the particular accelerating bucket being used, and we verify its accuracy with particle-in-cell simulations using laser drivers with energies in the Joule range.

physics.plasm-ph↗

arXiv2022

The AWAKE Run 2 programme and beyond

Plasma wakefield acceleration is a promising technology to reduce the size of particle accelerators. Use of high energy protons to drive wakefields in plasma has been demonstrated during Run 1 of the AWAKE programme at CERN. Protons of energy 400 GeV drove wakefields that accelerated electrons to 2 GeV in under 10 m of plasma. The AWAKE collaboration is now embarking on Run 2 with the main aims to demonstrate stable accelerating gradients of 0.5-1 GV/m, preserve emittance of the electron bunches during acceleration and develop plasma sources scalable to 100s of metres and beyond. By the end of Run 2, the AWAKE scheme should be able to provide electron beams for particle physics experiments and several possible experiments have already been evaluated. This article summarises the programme of AWAKE Run 2 and how it will be achieved as well as the possible application of the AWAKE scheme to novel particle physics experiments.

physics.acc-ph↗

arXiv2021

Particle-In-Cell Simulation using Asynchronous Tasking

Recently, task-based programming models have emerged as a prominent alternative among shared-memory parallel programming paradigms. Inherently asynchronous, these models provide native support for dynamic load balancing and incorporate data flow concepts to selectively synchronize the tasks. However, tasking models are yet to be widely adopted by the HPC community and their effective advantages when applied to non-trivial, real-world HPC applications are still not well comprehended. In this paper, we study the parallelization of a production electromagnetic particle-in-cell (EM-PIC) code for kinetic plasma simulations exploring different strategies using asynchronous task-based models. Our fully asynchronous implementation not only significantly outperforms a conventional, synchronous approach but also achieves near perfect scaling for 48 cores.

cs.DC↗

arXiv2021

Quantum Electrodynamics vacuum polarization solver

The self-consistent modeling of vacuum polarization due to virtual electron-positron fluctuations is of relevance for many near term experiments associated with high intensity radiation sources and represents a milestone in describing scenarios of extreme energy density. We present a generalized finite-difference time-domain solver that can incorporate the modifications to Maxwell's equations due to vacuum polarization. Our multidimensional solver reproduced in one-dimensional configurations the results for which an analytic treatment is possible, yielding vacuum harmonic generation and birefringence. The solver has also been tested for two-dimensional scenarios where finite laser beam spot sizes must be taken into account. We employ this solver to explore different types of laser configurations that can be relevant for future planned experiments aiming to detect quantum vacuum dynamics at ultra-high electromagnetic field intensities.

physics.plasm-ph↗

arXiv2021

Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interactions

We identify a mechanism for magnetic field generation in the interaction of intense electromagnetic waves and underdense plasmas. We show that Raman scattered plasma waves trap and heat the electrons preferentially in their propagation direction, resulting in a temperature anisotropy. In the trail of the laser pulse, we observe magnetic field growth which matches the Weibel mechanism due to the temperature anisotropy. We discuss the role of the initial electron temperature in our results. The predictions are confirmed with multi-dimensional particle-in-cell simulations. We show how this configuration is an experimental platform to study the long-time evolution of the Weibel instability.

physics.plasm-ph↗

arXiv2020

Plasma wakes driven by photon bursts via Compton scattering

Photon bursts with a wavelength smaller than the plasma inter-particle distance can drive plasma wakes via Compton scattering. We investigate this fundamental process analytically and numerically for different photon frequencies, photon flux, and plasma magnetization. Our results show that Langmuir and extraordinary modes are driven efficiently when the photon energy density lies above a certain threshold. The interaction of photon bursts with magnetized plasmas is of distinguished interest as the generated extraordinary modes can convert into pure electromagnetic waves at the plasma/vacuum boundary. This could possibly be a mechanism for the generation of radio waves in astrophysical scenarios in the presence of intense sources of high energy photons.

physics.plasm-ph↗

arXiv2016

Seeded QED cascades in counter propagating laser pulses

The growth rates of seeded QED cascades in counter propagating lasers are calculated with first principles 2D/3D QED-PIC simulations. The dependence of the growth rate on laser polarization and intensity are compared with analytical models that support the findings of the simulations. The models provide an insight regarding the qualitative trend of the cascade growth when the intensity of the laser field is varied. A discussion about the cascade's threshold is included, based on the analytical and numerical results. These results show that relativistic pair plasmas and efficient conversion from laser photons to gamma rays can be observed with the typical intensities planned to operate on future ultra-intense laser facilities such as ELI or VULCAN.

physics.plasm-ph↗

arXiv2014

A robust plasma-based laser amplifier via stimulated Brillouin scattering

It is shown here that Brillouin amplification can be used to produce picosecond pulses of petawatt power. Brillouin amplification is far more resilient to fluctuations in the laser and plasma parameters than Raman amplification, making it an attractive alternative to Raman amplification. Through analytic theory and multi-dimensional computer simulations, a novel, well-defined parameter regime has been found, distinct from that of Raman amplification, where pump-to-probe compression ratios of up to 100 and peak laser fluences over 1 kJ/cm$^2$ with 30\% efficiency have been achieved. High pulse quality has been maintained through control of parasitic instabilities.

physics.plasm-ph↗