
Figure showing the equipotential contours surrounding an ion passing through a strongly magnetized plasma.
Most plasmas are weakly magnetized in the sense that the gyrofrequency is much smaller than the plasma frequency (or equivalently, the gyroradius is larger than the Debye length). In these plasmas, the magnetic field is not strong enough to influence the trajectories at the microscopic length scales at which Coulomb collisions occur (within a Debye length). However, there are many plasmas in which the magnetic field is so strong that it influences the trajectories of the particles during Coulomb collisions. These plasmas are called strongly magnetized and occur in many experiments, such as magnetic confinement fusion, nonneutral plasmas, ultracold neutral plasmas, magnetized dusty plasmas, pulsed power devices, electron cooling devices, trapped antimatter and naturally occurring plasmas in planetary magnetospheres and neutron star atmospheres. Traditional plasma theories inherently assume that plasmas are weakly magnetized and, thus, unsuitable to model these experiments.
Our work seeks to develop a basic theoretical understanding of the properties of strongly magnetized plasmas, and to search for new physics that may be utilized in applications. The theoretical framework to understand the fundamental properties of these plasmas use both the Boltzmann kinetic theory approach and linear response formalism. New theories developed is tested using first-principles molecular dynamics simulations.
So far we have developed a generalized Boltzmann kinetic theory for strongly magnetized plasmas. The Boltzmann equation is generalized in this theory to account for the Lorentz force acting on particles during binary collisions. We have applied the theory to calculate the momentum and energy relaxation process of a test ion interacting with strongly magnetized and strongly coupled electrons. A few highlights of the results are:
1. Transverse force: Frictional drag usually acts antiparallel to the velocity of the test ion. Theoretical and molecular dynamics results showed that under conditions of strong magnetization, the frictional drag on the ion due to the electrons has a transverse component perpendicular to the ion velocity (in the plane of the velocity and magnetic field). This transverse force does not occur at weak magnetization and significantly alters the trajectory of the test ion.
2. Gyrofriction force: Under strong coupling and strong magnetization conditions, there is a third component of the frictional drag on the test ion that is in the direction of the Lorentz force. Again, this is absent at weak magnetization. It causes a shift of the test ion’s gyrofrequency.
3) Barkas effect: A fundamental property of traditional plasma kinetic theory is that the Coulomb collision rate does not depend on the sign of the interaction charges. For example, the same rates would be predicted for ions’ interaction with positrons or electrons. The theory and MD results show that this symmetry is broken when the plasma is strongly coupled and/or strongly magnetized. In particular, strong magnetization was found to change the momentum relaxation rates of the test ion by an order of magnitude compared to the unmagnetized results.
4) Ion-electron temperature relaxation: Our theory calculations have shown that in strongly magnetized plasmas, ion-electron temperature relaxation rates parallel and perpendicular temperatures are no longer equal, which can lead to the development of temperature anisotropy during temperature evolution. It was also found that the combination of oppositely charged interactions and strong magnetization caused the ion-electron relaxation rate in the parallel direction to be significantly suppressed, scaling inversely proportional to the magnetic field strength.
Publications related to this topic
[13] | Theory of the Ion-Electron Temperature Relaxation Rate in Strongly Magnetized Plasmas L. Jose, and S. D. Baalrud Physics of Plasmas 30 052103 (2023) |
[12] | Barkas Effect in Strongly Magnetized Plasmas L. Jose, D. J. Bernstein and S. D. Baalrud Physics of Plasmas 29 112103 (2022) |
[11] | dc Electrical Conductivity in Strongly Magnetized Plasmas S. D. Baalrud and T. Lafleur Physics of Plasmas 28 102107 (2021) |
[10] | A Kinetic Model of Friction in Strongly Coupled Strongly Magnetized Plasmas L. Jose and S. D. Baalrud Physics of Plasmas 28 072107 (2021) |
[9] | Effects of Coulomb Coupling on Friction In Strongly Magnetized Plasmas D. Bernstein and S. D. Baalrud Physics of Plasmas 28 062101 (2021) |
[8] | Extended Space and Time Correlations in Strongly Magnetized Plasmas K. Vidal and S. D. Baalrud Physics of Plasmas 28 042103 (2021) |
[7] | Viscosity of the Magnetized Strongly Coupled One-Component Plasma B. Scheiner, and S. D. Baalrud Physical Review E 102 063202 (2020) |
[6] | A Generalized Boltzmann Kinetic Theory for Strongly Magnetized Plasmas with Application to Friction L. Jose and S. D. Baalrud Physics of Plasmas 27 112101 (2020) |
[5] | Friction Force in Strongly Magnetized Plasmas D. J. Bernstein, T. Lafleur, J. Daligaut and S. D. Baalrud Physical Review E 102 041201(R) (2020) |
[4] | Friction in a Strongly Magnetized Neutral Plasma T. Lafleur and S. D. Baalrud Plasma Physics and Controlled Fusion 62, 095003 (2020) |
[3] | Transverse Force Induced by a Magnetized Wake T. Lafleur and S. D. Baalrud Plasma Physics and Controlled Fusion 61, 125004 (2019) |
[2] | Reduction of Electron Heating by Magnetizing Ultracold Neutral Plasma S. K. Tiwari and S. D. Baalrud Physics of Plasmas 25, 013511 (2018) |
[1] | Transport Regimes Spanning Magnetization-Coupling Phase Space S. D. Baalrud and J. Daligault Physical Review E 96, 043202 (2017) |