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DOE OSTI2022

Integrating a ponderomotive guiding center algorithm into a quasi-static particle-in-cell code based on azimuthal mode decomposition

High fidelity modeling of plasma based acceleration (PBA) requires the use of three dimensional, fully nonlinear, and kinetic descriptions based on the particle-in-cell (PIC) method. In PBA an intense particle beam or laser (driver) propagates through a tenuous plasma whereby it excites a plasma wave wake. Three-dimensional PIC algorithms based on the quasi-static approximation (QSA) have been successfully applied to efficiently model the interaction between relativistic charged particle beams and plasma. In a QSA PIC algorithm, the plasma response to a charged particle beam or laser driver is calculated based on forces from the driver and self-consistent forces from the QSA form of Maxwell's equations. These fields are then used to advance the charged particle beam or laser forward by a large time step. Since the time step is not limited by the regular Courant-Friedrichs-Lewy (CFL) condition that constrains a standard 3D fully electromagnetic PIC code, a 3D QSA PIC code can achieve orders of magnitude speedup in performance. Recently, a new hybrid QSA PIC algorithm that combines another speedup technique known as an azimuthal Fourier decomposition has been proposed and implemented. This hybrid algorithm decomposes the electromagnetic fields, charge and current density into azimuthal harmonics and only the Fourier coefficients need to be updated, which can reduce the algorithmic complexity of a 3D code to that of a 2D code. Modeling the laser-plasma interaction in a full 3D electromagnetic PIC algorithm is very computationally expensive due the enormous disparity of physical scales to be resolved. In the QSA the laser is modeled using the ponderomotive guiding center (PGC) approach. We describe how to implement a PGC algorithm compatible for the QSA PIC algorithms based on the azimuthal mode expansion. Here this algorithm permits time steps orders of magnitude larger than the cell size and it can be asynchronously parallelized. Details on how this is implemented into the QSA PIC code that utilizes an azimuthal mode expansion, QPAD, are also described. Benchmarks and comparisons between a fully 3D explicit PIC code (OSIRIS), as well as a few examples related to laser wakefield acceleration, are presented.

97 MATHEMATICS AND COMPUTING↗

NASA NTRSDate not supplied

Spaceflight Medical Evacuation Risk Assessment Principles - A Qualitative Investigation

BACKGROUND Future human space exploration beyond Low Earth Orbit (LEO) will require innovative solutions in many areas, primarily those that provide direct medical support to crew on long-duration missions and optimize their health and performance. The associated challenges therein will be numerous, including but not necessarily limited to extended one-way or "asynchronous" communication delays, minimal to non-existent resupply, and a prolonged transit time to "definitive care" ranging from 3-days to 9-months. At the same time, long-duration exploration spacecraft and crew will face restrictions on mass, power, volume, and data far more significant than that seen in current LEO settings. Given these limitations, medical risk assessment is of primary importance, especially evaluating the implications of a medical evacuation of an ill or injured crewmember. Such evacuations are complicated, potentially dangerous, and well may be impossible in certain phases of the mission. Regardless, such issues must be weighed against the risks of the injured crew remaining aboard a spacecraft with limited medical resources. OBJECTIVE This qualitative study drew from the experiences of subject matter experts (SMEs) in spaceflight and appropriate analog environments (i.e., military, disaster, and extreme environment fields) to identify unique principles common amongst medical evacuation considerations helpful in informing future risk assessment tools. Appropriate analog environments included austere operational settings where multiple factors (weather, logistics/limited resupply, denied/extreme environments, and patient condition) resulted in a limited ability to provide definitive local medical care. The fundamental principles in question revolved around scenarios where evacuation became a complicating yet necessary consideration and where life-threatening medical concerns had to be weighed against critical mission objective(s). The primary authors collected semi-structured data gathered through in-depth interviews with 16 subject matter experts (SMEs). Interview questions investigated how these SMEs consider and weigh the attendant risks present in medical evacuation scenarios. Among the critical questions posed were those that sought to understand how the SME balanced the challenges and requirements of medical evacuation (or keeping an injured patient "on-site" aka: "prolonged field care") against the evacuation operation's risks on impacting overarching mission success. The team analyzed interview transcripts for common themes and principles using the qualitative methods of thematic analysis based on consensus, co-occurrence, and comparison. As a result, nine primary risk consideration themes and nine contributing factor themes emerged, all of which will ideally inform future medical evacuation decision-making tools and operational decision-making for exploration class missions. Specific aims for this study included: 1. Identification of common principles used to assess risks and benefits of medical evacuations in extreme environments 2. Identification of common points of friction or complication and challenges in extreme environment evacuations

A T Almand↗

DOE OSTI2019

PRIMA-X - Performance Retargeting of Instrumentation, Measurement, and Analysis Technologies for Exascale Computing

The PRIMA-X (Performance Retargeting of Instrumentation, Measurement, and Analysis Technologies for Exascale Computing) project is the successor of the DOE PRIMA (Performance Refactoring of Instrumentation, Measurement, and Analysis Technologies for Petascale Computing) project, which addressed the challenge of creating a core measurement infrastructure that would serve as a common platform for both integrating leading parallel performance systems (notably TAU and Scalasca) and developing next-generation scalable performance tools. The PRIMA-X project shifts the focus away from refactorization of robust performance tools towards a re-targeting of the parallel performance measurement and analysis architecture for extreme scales. The massive concurrency, asynchronous execution dynamics, hardware heterogeneity, and multi-objective prerequisites (performance, power, resilience) that identify exascale systems introduce fundamental constraints on the ability to carry forward existing performance methodologies. In particular, there must be a deemphasis of per-thread observation techniques to significantly reduce the otherwise unsustainable flood of redundant performance data. Instead, it will be necessary to assimilate multi-level resource observations into macroscopic performance views, from which resilient performance metrics can be attributed to the computational features of the application. This requires a scalable framework for node-level and system-wide monitoring and runtime analyses of dynamic performance information. Also, the interest in optimizing parallelism parameters with respect to performance and energy drives the integration of tool capabilities in the exascale environment further. Initially, PRIMA-X was a collaborative project between the University of Oregon (lead institution) and the German Research School for Simulation Sciences (GRS). Because Prof. Wolf, the PI at GRS, accepted a position as full professor at Technische Universitaet Darmstadt (TU Darmstadt) starting February 1st, 2015, the work of GRS was continued at TU Darmstadt. This report covers the work at TU Darmstadt after the transition. The first main accomplishment of TU Darmstadt is the development of different techniques to aggregate performance data on the level of threads. TU Darmstadt evaluated different schemes designed at GRS during the first phase of this project and integrated them into Score-P, a widely used performance measurement framework for HPC applications. The second main accomplishment is a substantial increase of Score-P’s scalability, achieved by improving its internal representation of the underlying system. Third, we extended our performance-modeling tool Extra-P to automatically create models with more than one input parameter (e.g., process count and input size), which was previously impossible. These models allow the performance behavior of an application to be extrapolated to larger machines. Specific applications of the new multi-parameter capability realized in this project include modeling the isoefficiency function of task-based applications and a novel co-design methodology. Further extensions of Extra-P comprise online modeling functionality, automatic refinement of the model search space, and segmented performance modeling. Further contributions include new locality metrics for both shared- and distributed-memory applications, a new way of measuring the impact of inter-application inference on the execution time of an application, and finally an automatic method that selects appropriate OpenMP constructs for the parallelization of sequential code and classifies the affected variables based on their sharing semantics.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2022

Reionization time of the Local Group and Local-Group-like halo pairs

ABSTRACT Patchy cosmic reionization resulted in the ionizing UV background asynchronous rise across the Universe. The latter might have left imprints visible in present-day observations. Several numerical simulation-based studies show correlations between the reionization time and overdensities and object masses today. To remove the mass from the study, as it may not be the sole important parameter, this paper focuses solely on the properties of paired haloes within the same mass range as the Milky Way. For this purpose, it uses CoDaII, a fully coupled radiation hydrodynamics reionization simulation of the local Universe. This simulation holds a halo pair representing the Local Group, in addition to other pairs, sharing similar mass, mass ratio, distance separation, and isolation criteria but in other environments, alongside isolated haloes within the same mass range. Investigations of the paired halo reionization histories reveal a wide diversity although always inside-out, given our reionization model. Within this model, haloes in a close pair tend to be reionized at the same time but being in a pair does not bring to an earlier time their mean reionization. The only significant trend is found between the total energy at z = 0 of the pairs and their mean reionization time: Pairs with the smallest total energy (bound) are reionized up to 50 Myr earlier than others (unbound). Above all, this study reveals the variety of reionization histories undergone by halo pairs similar to the Local Group, that of the Local Group being far from an average one. In our model, its reionization time is ∼625 Myr against 660 ± 4 Myr (z ∼ 8.25 against 7.87 ± 0.02) on average.

79 ASTRONOMY AND ASTROPHYSICS↗