Self-Generated Coronal Magnetic Fields in High Energy Density Plasmas

University Of Rochester, Rochester NY

Investigators

Abstract

This award supports a computational study of how magnetic fields can be generated in astrophysical and laboratory plasmas, which are collections of many electrically charged particles interacting with each other. It is well known that magnetic fields can strongly impact how plasmas behave, but the mechanisms for self-generation of magnetic field in different types of plasma continue to be a mystery. Self-generated magnetic fields are ubiquitous in many astrophysical environments and determine the evolution of such systems, with the 22-year solar cycle of magnetic activity being one of many examples. Self-generated magnetic fields in laser-driven plasmas can also be strong enough to significantly modify the plasma behavior. This project will help explain the processes giving rise to magnetic fields in plasmas irradiated by stars in gas nebulae or by lasers in the laboratory. It will also aid in better understanding thermodynamic transport properties in laboratory and astrophysical plasma systems. For example, observations of gas nebulae morphologies from current and future astronomical observatories, such as ALMA and JWST, stand to benefit from the development and testing of the theory developed in this project. The goal of this project is to identify the main mechanisms by which magnetic fields are self-generated in irradiated plasmas subject to instabilities. Self-generated magnetic fields in irradiated plasmas are often produced by the Biermann battery effect. Magnetic fields can also be driven by the Rayleigh-Taylor (RT) instability in radiation-driven plasmas. RT induced fields are confined near the ablation front by the Nernst flow and do not affect the coronal plasma properties. However, in laboratory plasmas irradiated by a laser, strong B-fields have been observed in the coronal plasma using proton radiography, in addition to the standard Biermann battery fields surrounding the laser spot. It has been speculated that the magneto-thermal instability (MTI) is the main source of mega-gauss magnetic fields in the corona of laser-driven plasmas; yet, recent work has shown that the traditional form of MTI is suppressed by supersonic plasma flows. This leaves an important open question on what is responsible for the coronal magnetic fields observed in laboratory settings. This project will investigate new instability mechanisms which can generate magnetic fields that are sufficiently strong to explain observations, including the electro-thermal instability and new forms of the magneto thermal instability localized where the flow velocity equals the Nernst velocity. The work will involve theoretical analysis and numerical simulations. 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.