Friction force in strongly magnetized plasmas

Temperature relaxation rates in strongly magnetized plasmas

Strongly magnetized plasmas, characterized by having a gyrofrequency larger than the plasma frequency (β=ω_{c}/ω_{p}≫1), are known to exhibit novel transport properties. Previous works studying pure electron plasmas have shown that strong magnetization significantly inhibits energy exchange between parallel and perpendicular directions, leading to a prolonged time for relaxation of a temperature anisotropy. Recent work studying repulsive electron-ion interactions (e^{-}-i^{-} or e^{+}-i^{+}) showed that strong magnetization increases both the parallel and perpendicular temperature relaxation rates of ions, but in differing magnitudes, resulting in the formation of temperature anisotropy during equilibration. This previous study treated electrons as a heat bath and assumed weak magnetization of ions. Here, we broaden this analysis and compute the full temperature and temperature anisotropy evolution over a broad range of magnetic field strengths. It is found that when electrons are strongly magnetized (β_{e}≫1) and ions are weakly magnetized (β_{i}≪1), the magnetic field strongly suppresses the perpendicular energy exchange rate of electrons, whereas the parallel exchange rate slightly increases in magnitude compared to the value at weak magnetization. In contrast, the ion perpendicular and parallel energy exchange rates both increase in magnitude compared to the values at weak magnetization. Consequently, equilibration causes the electron parallel temperature to rapidly align with the ion temperature, while the electron perpendicular temperature changes much more slowly. It is also shown that when both ions and electrons are strongly magnetized (β_{i},β_{e}≫1), the ion-electron perpendicular relaxation rate dramatically decreases with magnetization strength.

Effect of Strongly Magnetized Electrons and Ions on Heat Flow and Symmetry of Inertial Fusion Implosions

This Letter presents the first observation on how a strong, 500 kG, externally applied B field increases the mode-two asymmetry in shock-heated inertial fusion implosions. Using a direct-drive implosion with polar illumination and imposed field, we observed that magnetization produces a significant increase in the implosion oblateness (a 2.5× larger P2 amplitude in x-ray self-emission images) compared with reference experiments with identical drive but with no field applied. The implosions produce strongly magnetized electrons (ω_{e}τ_{e}≫1) and ions (ω_{i}τ_{i}>1) that, as shown using simulations, restrict the cross field heat flow necessary for lateral distribution of the laser and shock heating from the implosion pole to the waist, causing the enhanced mode-two shape.

Impact of magnetic field on the parallel resistivity

The impact of magnetic field (MF) on the parallel resistivity η_{∥} is studied for strongly magnetized plasmas with the electron thermal gyroradius ρ_{the} smaller than the Debye length λ_{D} but much larger than the Landau length λ_{L}. Two previous papers [P. Ghendrih et al., Phys. Lett. A 119, 354 (1987)10.1016/0375-9601(87)90614-1; S. D. Baalrud and T. Lafleur, Phys. Plasmas 28, 102107 (2021)10.1063/5.0054113] found η_{∥} to increase monotonically with MF. Unfortunately, both works used predetermined electron distribution functions and are thus not self-consistent. In this paper, we analyze the MF dependence of η_{∥} self-consistently by solving the electron magnetized kinetic equation in a Lorentz gaslike approximation. It is found η_{∥} decreases monotonically with MF, with λ_{D} in the usual Coulomb logarithm lnΛ=ln(λ_{D}/λ_{L}) being replaced by ρ_{the}. The underlying physics is that the electrons affected only by the collisions with impact parameters between λ_{L} and ρ_{the} carry almost all the parallel current.

Viscosity of the magnetized strongly coupled one-component plasma

The viscosity tensor of the magnetized one-component plasma, consisting of five independent shear viscosity coefficients, a bulk viscosity coefficient, and a cross coefficient, is computed using equilibrium molecular dynamics simulations and the Green-Kubo relations. A broad range of Coulomb coupling and magnetization strength conditions are studied. Magnetization is found to strongly influence the shear viscosity coefficients when the gyrofrequency exceeds the Coulomb collision frequency. Three regimes are identified as the Coulomb coupling strength and magnetization strength are varied. The Green-Kubo relations are used to separate kinetic and potential energy contributions to each viscosity coefficient, showing how each contribution depends upon the magnetization strength. The shear viscosity coefficient associated with the component of the pressure tensor parallel to the magnetic field, and the two coefficients associated with the component perpendicular to the magnetic field, are all found to merge to a common value at strong Coulomb coupling.