This study presents a multiphysics and multiscale simulation of the interaction between a relativistic pulsed electron beam produced by a Marx generator with a metallic target. In a first step of the calculation series, the operation of the generator is calculated using a 2D Maxwell-Vlasov Particle-In-Cell code. This calculation step allows for the electromagnetic coupling between the generator and the self-magnetic pinch (SMP) diode and restores the spectral and angular characteristics of the electron beam impacting the anode. From these electron characteristics, the energy deposition of the electron beam into the target is computed via a 3D Monte Carlo method in a second step. This energy deposition is then used as the entrance parameter of a 1D hydrodynamic calculation in a third step. The different results of this calculation series are compared with experimental measurements such as the current and the voltage of the diode, electron beam focal spot, dose rate, target deformation velocity, and plasma temperature and density. This approach, combining calculation and experimental measurements, provides a precise quantification of the mechanisms at work when a target is exposed to a high dose rate. The applications of this analysis method concern the framework of the influence of the impedance collapse during the operation of SMP electron diodes and the generation of well-defined mechanical stresses for the validation of equation of states and the modeling of fracturing under high pressures.
Compute centers have passed through several major evolutions during the past 30 years. From the storage systems perspective, the evolution has fundamentally changed the way data is structured, represented, stored and accessed, moving from supercomputer attached file systems to massively distributed services. Throughout this period, new hardware technologies, whether for computing or for data storage, have in turn brought major changes, even broken new ground, and posed real scientific challenges. To address these challenges, innovative concepts and paradigms have been introduced with various implementations and integrated into large-scale solutions which remain in continuous evolution, reconciling hardware advances, application requirements, and contextual constraints. This article retraces the milestones of this technological journey in a chronological order, starting with the Petascale period and the introduction of IO-Proxies to meet the need for increasing storage capacity and reduced access latency, exploring a wealth of data structures, protocols, and other software components to build parallel, efficient and scalable solutions. The challenges of the Exascale era were even greater and innovations were introduced to address them, especially in terms of scheduling policies to match the complexity of the associated workflows and dataflows. Then, the IO-Proxies evolved to a more versatile paradigm implementing the Ephemeral Services.
Hypervelocity impacts (HVI) with millimeter or submillimeter projectiles can strike aerospace structures with relative velocities of several km/s. In the present paper, the effect of temperature, in the range of 300 to 3600 K, on the size of the craters produced by HVI on graphite targets is studied. This study was made possible by the development of an original experimental setup based on the use of two high-power lasers: a nanosecond shock laser delivering up to 40 J to simulate impacts of 260 mu m diameter aluminum projectiles at velocities ranging from 2 to 4 km/s, and a continuous-wave heating laser in order to reach very high temperatures with a brief heating time and well-controlled heating ramp. This study shows that maximum depth and diameter of craters do not vary with the temperature up to 3400 K, but a slight increase of the crater volume is observed. It is explained by a more complete formation of the crater at high temperature. This behavior was not clear up to now in the literature, probably because of the effect of sublimation at high temperature which can be taken into account by the present methodology. Beyond 3400 K, a rapid decrease of crater dimensions is observed.
The impact on electron lifetimes of nonlinear interactions with the most intense very low frequency (VLF) waves from transmitters has hitherto been neglected in radiation belt codes. Here, we show the presence of a small population of intense wave packets, originating from ground‐based VLF transmitters and reaching 10 mV/m around the magnetic equator at , in burst mode data from the Van Allen Probes. Despite their very small occurrence rate, such intense wave packets may carry of the order of 25% of the total electric field wave power of VLF waves from transmitters. Using test particle simulations, we demonstrate that the long‐term effects of electron nonlinear interactions with such intense wave packets through Landau and cyclotron resonances can be modeled by electron advection rates coupled with nonlinear diffusion rates, in both pitch‐angle and energy space. These numerically determined rates allow us to estimate the impact of these nonlinear interactions on electron loss timescales. We show that these rare nonlinear interactions could lead to a significantly faster decay of trapped 30–75 keV electron fluxes at than usual quasi‐linear interactions with moderate time‐averaged amplitude waves and Coulomb collisions. This may contribute to explain the short 30–75 keV electron lifetimes measured by the Van Allen Probes in this region, as well as observations of flattened electron flux energy spectra. Nonlinear interactions also increase the energy of precipitated electrons. This suggests a potential long‐term impact of nonlinear wave‐particle interactions on energetic electron fluxes in the inner radiation belt.
Methods for location of infrasonic and low frequency sound sources allow to reconstruct complex lightning geometries, including simultaneously cloud‐to‐ground return strokes and intracloud discharges. Back‐propagating the ground recorded pressure also provides an estimation of the sound source power distribution within a lightning flash, by compensating for propagation effects. Acoustics is therefore a unique observation means for evaluating lightning energy distribution both within and below the thundercloud. Using a thunder database recorded in the (1–100) Hz frequency range during two observation campaigns in Southern France in 2012 and 2018, the vertical repartition of thunder power is investigated statistically over a significant number of flashes, with a majority of negative cloud‐to‐ground (CG−) events. This repartition is also discussed per sound frequency band. Rare positive cloud‐to‐ground (CG+) events having lead to sprites (transient luminous events above the cloud in the mesosphere) and a few, entirely intracloud discharges, are also analyzed. Acoustic data are complemented by electromagnetic very high frequency (EM‐VHF [60–66] MHz range) detections by Lightning Mapping Arrays for the same events. Vertical localizations of sound and EM‐VHF powers within the different thundercloud charged layers are compared. For CG− discharges however, most of the sound power is shown to be emitted along the cloud to ground plasma channels, at an average altitude around 1 km only well below the cloud.
