Anatoly Spitkovsky, Ph.D. - US grants

AST-0807381
Spitkovsky

Acceleration of particles in collisionless shocks is at the heart of most models of nonthermal phenomena in the Universe, including pulsar wind nebulae, active galactic nuclei, gamma-ray bursts, and supernova remnants. The conversion of flow energy into relativistic particles is usually attributed to the first-order Fermi mechanism, but this is not well understood. This project will construct a self-consistent theory of shock acceleration by performing the first large-scale three-dimensional particle-in-cell (PIC) simulations of astrophysical collisionless shocks. The PIC method is the most fundamental ab initio approach to plasma dynamics that is able to resolve directly the complex microphysics of plasma instabilities, particle scattering, and magnetic field generation near shocks. Specific questions to be addressed include: 1) Do collisionless shocks generate significant magnetic fields that can survive far downstream? 2) What fraction of shocked particles is injected into the Fermi mechanism? 3) What is the effect of high-energy particles on shock hydrodynamics and magnetic field amplification? 4) What mechanisms cause equilibration between particle species in shocks? This study will be a definitive test of the prevailing hypothesis that Fermi acceleration in collisionless shocks is the origin of high energy cosmic rays and nonthermal particles in a variety of astrophysical sources.

The results will be of broad significance to observers, experimentalists, and theorists involved with experiments to study high-energy astrophysical and cosmological sources. The research integrates research and education by involving graduate and undergraduate students, and postdocs, training in numerical modeling and visualization of multiscale systems. An offshoot will be a comprehensive web-based introduction to the physics of collisionless shocks. In addition, a new version of the massively-parallel PIC code TRISTAN-MP and its analysis tools will be publicly released and supported on the web site.

Proposal #: 12-29573
PI(s): Hillegas, Curtis W.
Carter, Emily A.; Pretorius, Frans; Spitkovsky, Anatoly; Wood, Eric F.
Institution: Princeton University
Title: MRI/Acq.: Shared Parallel High Performance Storage System to Enable Computational Science and Engineering
Project Proposed:
This project, acquiring a High Performance Computing (HPC) storage system, aims to provide storage and I/O bandwidth required to enable advancement of research to new, previously unattainable areas. Specifically, in astrophysics the storage will allow an increase in dimensionality to perform full 3D modeling of shock formation; in civil and environmental engineering, it will enable the analysis of higher resolution water condition data in both time and space; in mechanical and aerospace engineering, the instrument will facilitate rigorous physical modeling of rate constants for biofuel combustion and fundamental understanding of molecular adsorptions; and in physics it will enable the modeling of gravitational waves and compact object mergers considering a broader range of physics. More generally, the system will enable projects across many disciplines in computational science and engineering.
Since data storage and access have become a bottleneck hampering researchers in the TIGRESS systems, the proposed system should contribute to remove the bottleneck. Understanding that data growth will continue, a modular storage system design has been chosen that will allow the system to grow in capacity and performance as the data deluge continuous to mount. Planned is the purchase of a 1.5 PB storage system based on hardware from NetApp, integrated with servers from SGI by Comnetco. The system will run IBMs General Parallel File System (GPFS) and provide 12 GB/s parallel performance across the institution?s TIGRESS HPC systems.
Broader Impacts:
The instrument will facilitate collaboration by making it easy for researchers to share data within the institution; furthermore, it will foster collaboration nationally and internationally through the included web server facility by allowing researchers to broadly share their data. As a research tool available to postdocs, graduate students, and advanced undergraduate students, including many researchers underrepresented minority groups, the instrument will serve as a training platform, teaching data layout, management and performance optimization.

This project will study how particles get accelerated to high speeds in astrophysical sources, focusing on a special mechanism known as Fermi acceleration. Although it is believed that a considerable fraction of the energy in material flowing around pulsars, supernovae, and other strong sources, can be converted into very fast particles, which are identified by the patterns of radiation they give off, the mechanism is not well understood. After this study, the Fermi mechanism will be much better characterized, and may be tightly constrained.

Acceleration of particles in collisionless shocks is at the heart of most models of non-thermal phenomena in the Universe. Observations of synchrotron emission suggest that such shocks in pulsar wind nebulae, in jets from active galactic nuclei, in gamma-ray bursts, and in supernova remnants, can convert a significant fraction of the flow energy into relativistic particles with power-law spectra. However, although it is usually invoked as the cause, the conditions for operation of the first-order Fermi mechanism and its efficiency are not understood from first principles. This project will construct a self-consistent theory of shock acceleration by performing large-scale multidimensional particle-in-cell and hybrid simulations of astrophysical collisionless shocks, and study the microphysics of plasma instabilities, particle scattering, and magnetic field generation, necessary to calibrate nonlinear diffusive shock acceleration theory. Specific questions include: 1) the criteria for existence of shock acceleration, and its efficiency; 2) how accelerated particles influence shock structure and evolution; 3) the proton and electron spectra generated in realistic shocks. The tools developed during this work will enable multi-scale modeling of shocks and will derive particle spectra in the nonlinear regime from first principles. This research will provide predictive power to the hypothesis that Fermi acceleration in collisionless shocks is the origin of high-energy cosmic rays and non-thermal particles, and could place tight constraints on the models of magnetization and on the composition of astrophysical outflows.

Because Fermi acceleration is a fundamental process in astrophysics, the results will be of value to observers, experimentalists, and theorists studying high-energy astrophysical and cosmological sources, and are even applicable to shocks in the solar system. The findings will guide a new generation of laboratory experiments. The work will involve postdocs, and graduate and undergraduate students, training them in numerical modeling and visualization, and thus preparing them for careers in science and technology fields, where large-scale computing increasingly plays an important role. An interactive plasma physics tutorial will be developed to bring intuitive understanding of these thorny subjects to specialists and the general public alike.

Most of the visible matter in the Universe is a plasma, that is a dilute gas of ions, electrons, and neutral particles. Many fundamental and important physical processes that occur in plasmas remain poorly understood. This, in turn, limits our ability to understand diverse phenomena in space such as how stars form or how the particles flowing from the Sun affect the upper layers of the Earth's atmosphere. It also impacts our ability to engineer and operate experiments on Earth such as magnetically confined fusion devices. The Max-Panck Princeton Center for Plasma Physics (MPPC) was established as a joint venture of the Max Planck Society in Germany, Princeton University, and the Department of Energy's Princeton Plasma Physics Laboratory (PPPL) in order to forge new collaborations between Universities, the national plasma labs, and international partners in order to investigate some of the most pressing problems in plasma physics. By supporting students and early career scientists, the MPPC serves to train the next generation of experimental, computational, and theoretical plasma physicists, and its international scope provides unique training for early career scientists. The center provides unique opportunities for the public, as well as students and teachers at public and regional schools, to engage in scientific inquiry in ways that enhance their understanding of science concepts and scientific ways of thinking through a well established outreach program at PPPL.

The MPPC effort at Princeton University is focused on three cross-cutting problems in plasma astrophysics: cosmic ray transport and feedback, the interplay between turbulence and reconnection, and dynamo action in accretion disks, stellar convection, and galaxies. New fluid closure models for cosmic rays will be developed and applied to models of the interstellar medium in galaxies to understand the role of cosmic-ray feedback on galaxy formation. New theoretical and computational studies of magnetic field amplification by dynamo action driven by the magneto-rotational instability in accretion disks, and convection in rotating stars, will be undertaken. Using new computational tools developed by members of the MPPC, new studies of plasma turbulence in the kinetic regime, relevant to conditions in the solar wind, will be developed. The Center fosters interdisciplinary collaboration between the plasma and astrophysics communities, as well as international collaboration between these communities in the US, Germany, and elsewhere. Its international scope provides unique training for graduate students and postdocs. This award provides renewed support for Princeton University's participation in MPPC, with support for PPPL's participation provided by the Department of Energy.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This award establishes a multi-institutional and international collaborative Multi-messenger Plasma Physics Center (MPPC) focused on studying fundamental plasma processes with the goal of modeling sources of astrophysical signals. Recent discoveries of gravitational waves from merging black holes and neutron stars and the detections of energetic neutrinos and ultra-high energy cosmic rays herald the rise of multi-messenger astronomy (MMA) aiming to observe the sky not only through light, but also through gravitational waves and energetic particles. Interpretation of MMA signals, however, crucially depends on our ability to understand, predict, and model the electromagnetic counterparts of multi-messenger sources. In most theories of these sources, the light is coming from a relativistic plasma that experiences very strong gravitational, magnetic and radiation fields. How plasmas produce the observable radiation under these conditions challenges our understanding of plasma physics. MPPC will study the fundamental processes in relativistic plasmas that lead to the observable emission from multimessenger sources, and thus addresses goals of NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics". The investigators will mentor summer research for undergraduate and high school students and will increase awareness of plasma astrophysics through introductory lectures at minority-serving undergraduate institutions and through public outreach. <br/><br/>The MPPC research will be concentrated in three areas: 1) basic physics of relativistic pair plasmas near compact objects, including radiative relativistic reconnection, pair creation, and interaction of strong waves with plasmas; 2) multi-scale modeling of compact objects, including the development of global models of merging neutron star magnetospheres, magnetar outbursts, black hole accretion disk flares, and particle acceleration in jets; 3) the physics of transport of cosmic rays in our galaxy, including streaming instabilities and interactions of cosmic rays with turbulence. The collaboration will develop models that will be used to predict electromagnetic precursors of neutron star mergers, constrain the sites of acceleration of ultra-high energy cosmic rays, and improve cosmic ray transport models for galactic wind driving. The Center will also provide scientific leadership in designing laboratory experiments for studying relativistic astrophysical plasmas with ultra-intense lasers. The Center includes four US nodes - Princeton University, Columbia University, University of Maryland, and Washington University in St. Louis, - and will have an international collaborative component with the participation of Max Planck Society institutes.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.