TIA: A forward model and analyzer for Talbot interferometry experiments of dense plasmas

Producción CientíficaInterferometry is one of the most sensitive and successful diagnostic methods for plasmas. However, owing to the design of most common interferometric systems, the wavelengths of operation and, therefore, the range of densities and temperatures that can be probed are severely limited. Talbot–Lau interferometry offers the possibility of extending interferometry measurements to x-ray wavelengths by means of the Talbot effect. While there have been several proof-of-concept experiments showing the efficacy of this method, it is only recently that experiments to probe High Energy Density (HED) plasmas using Talbot–Lau interferometry are starting to take place. To improve these experimental designs, we present here the Talbot-Interferometry Analyzer (TIA) tool, a forward model for generating and postprocessing synthetic x-ray interferometry images from a Talbot–Lau interferometer. Although TIA can work with any two-dimensional hydrodynamic code to study plasma conditions as close to reality as possible, this software has been designed to work by default with output files from the hydrodynamic code FLASH, making the tool user-friendly and accessible to the general plasma physics community. The model has been built into a standalone app, which can be installed by anyone with access to the MATLAB runtime installer and is available upon request to the authors

Dense plasma heating by crossing relativistic electron beams

Here we investigate, using relativistic fluid theory and Vlasov-Maxwell simulations, the local heating of a dense plasma by two crossing electron beams. Heating occurs as an instability of the electron beams drives Langmuir waves, which couple nonlinearly into damped ion-acoustic waves. Simulations show a factor 2.8 increase in electron kinetic energy with a coupling efficiency of 18%. Our results support applications to the production of warm dense matter and as a driver for inertial fusion plasmas

Phase imaging of irradiated foils at the OMEGA EP facility using phase-stepping X-ray Talbot–Lau deflectometry

Producción CientíficaDiagnosing the evolution of laser-generated high energy density (HED) systems is fundamental to develop a correct understanding of the behavior of matter under extreme conditions. Talbot–Lau interferometry constitutes a promising tool, since it permits simultaneous single-shot X-ray radiography and phase-contrast imaging of dense plasmas. We present the results of an experiment at OMEGA EP that aims to probe the ablation front of a laser-irradiated foil using a Talbot–Lau X-ray interferometer. A polystyrene (CH) foil was irradiated by a laser of 133 J, 1 ns and probed with 8 keV laser-produced backlighter radiation from Cu foils driven by a short-pulse laser (153 J, 11 ps). The ablation front interferograms were processed in combination with a set of reference images obtained ex situ using phase-stepping. We managed to obtain attenuation and phase-shift images of a laser-irradiated foil for electron densities above 1e22 cm−3. These results showcase the capabilities of Talbot–Lau X-ray diagnostic methods to diagnose HED laser-generated plasmas through high-resolution imaging.The work has been supported by Research Grant No. PID2019-108764RB-I00 from the Spanish Min istry of Science and Innovatio

Attosecond-scale absorption at extreme intensities

A novel non-ponderomotive absorption mechanism, originally presented by Baeva et al. in one dimension, is extended into higher dimensions for the first time. This absorption mechanism, the Zero Vector Potential (ZVP), is expected to dominate the interactions of ultra-intense laser pulses with critically over-dense plasmas such as those that are expected with the Extreme Light Infrastructure laser systems. It is shown that the mathematical form of the ZVP mechanism and its key scaling relations found by Baeva et al. in 1D are identically reproduced in higher dimensions. The two dimensional particle-in-cell simulations are then used to validate both the qualitative and quantitative predictions of the theory

Wakefields in a cluster plasma

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma

Referenceless, grating-based, single shot X-ray phase contrast imaging with optimized laser-driven K-α sources

Producción CientíficaWith its ability to efficiently probe low-Z materials, X-ray phase imaging methods have recently raised high interest in multiple fields from biology and medical applications to high energy density (HED) physics. Initially developed with synchrotron light and X-ray tubes, we present a novel grating based Talbot X-ray deflectometer (TXD) diagnostic that was coupled with laser-generated K-α X-ray sources. The multi-terawatt laser (I > 1 × 1014 W cm-2) was used as a testbed for diagnostic development. It was found that X-ray source chromaticity plays an important role in TXD. Indeed, the broadband spectrum of laser-generated X-ray sources may strongly impact image quality and thus diagnostic performance. We qualified X-ray emission from different laser-produced sources and determined laser, target, and deflectometer parameters that optimize TXD performance. We present the first results of referenceless grating-based X-ray imaging at high-power laser facilities and discuss the implications of this new development in HED research.This work has also been supported by the Research Grants No. PID2019-108764RB-I00 and PID2022-137632OB-I00 from the Spanish Ministry of Science and Innovation

Methodological and managerial applications of the structural norm approach to social and facility capacity indicators in Hawai'i's coastal recreation areas

Tropical coastal and marine areas are popular for recreation, leisure, and tourism activities, but these activities can cause social (e.g., crowding), ecological (e.g., coral trampling), and managerial impacts (e.g., pressure on facilities). The concept of norms is one approach for examining user acceptance or tolerance of these impacts. This dissertation consists of three standalone articles that extend the application of norms to social and facility impacts in tropical coastal and marine areas. The first article is methodological in nature, as it empirically compares one conventional scale ("very unacceptable" to "very acceptable") and one new scale ("should definitely not allow" to "should definitely allow") for measuring encounter norms in these areas. The second article then applies this scale to examine the influence of user value orientations toward coral reef areas (i.e., biocentric or protectionist to anthropocentric or use oriented) on norms regarding encounters in these areas. Given that there has been little empirical research on facility capacity issues, the third article extends the encounter – norm – observation approach to examine facility capacity issues in these areas. Data were obtained from onsite questionnaires administered to users at six sites on the island of Oahu, Hawai'i (n = 2,821; 87% response rate). Results of the first article showed that the new scale that was arguably more in line with conventional definitions of norms and related obligations generated higher norm intensity or importance of encounters as an indicator, but less crystallization or consensus and more liberal standards. These differences between scales were statistically significant across most sites, but were relatively weak, suggesting that the most commonly used scale for measuring norms in recreation, leisure, and tourism (i.e., acceptance) may still be appropriate. Results of the second article showed that the majority of users had a protectionist orientation toward coral reef areas and there was no group with only use orientations. Across most sites, those with stronger protectionist orientations toward reef areas were more likely to feel that higher use densities or encounters should not be allowed in these areas, had more crystallization about conditions that should and should not be allowed, and believed more strongly that use density was an important indicator for these areas. Results of the third article showed that the majority of users saw fewer of most facilities at each site than they believed should be at each site and these people were less satisfied with facilities. When compared to the actual number of facilities, however, there were enough of most facilities to accommodate respondent norms. A summary of findings, management implications, and considerations for future methodological and theoretical research is provided

Social and facility carrying capasities of coastal recreation areas on Oahu, Hawaii

As popularity of Hawaii\u27s beaches and coral reefs increases, there is a need to measure and monitor recreation carrying capacities and use thresholds to ensure that resources and experiences are not degraded. Objectives of this study were to estimate social and facility carrying capacities at various sites on the island of Oahu, Hawaii. Data were obtained from surveys completed by recreationists at each site in 2007 (n = 2,821, response rate = 87%). Results showed that reported encounters with other users, perceived crowding, and maximum tolerances for encountering other recreationists differed among sites. Despite high encounter rates at some sites, less than 55% of respondents at each site felt crowded. Between 63% and 75% of visitors at each site encountered fewer people than their maximum tolerance limit, suggesting that indicators of social carrying capacity were not being exceeded at any of the sites. Satisfaction with some facilities at each site was relatively low partially because most respondents reported encountering fewer facilities than what actually exists. At some sites, there were not enough facilities to accommodate current use and recreationists\u27 demands suggesting that some indicators of facility carrying capacity were being exceeded. Research and management implications will be discussed