Electron and Ion Heating during Magnetic Reconnection in Weakly Collisional Plasmas

Gyrokinetic simulations of magnetic reconnection are presented to investigate plasma heating for strongly magnetized, weakly collisional plasmas. For a low plasma beta case, parallel and perpendicular phase mixing strongly enhance energy dissipation yielding electron heating. Heating occurs for a long time period after a dynamical process of magnetic reconnection ended. For a higher beta case, the ratio of ion to electron dissipation rate increases, suggesting that ion heating (via phase-mixing) may become an important dissipation channel in high beta plasmas.Comment: 9 pages, 3 figures, accepted for publication in JPSJ Suppl. [Proceedings of the 12th Asia Pacific Physics Conference

Bifurcation in electrostatic resistive drift wave turbulence

The Hasegawa-Wakatani equations, coupling plasma density and electrostatic potential through an approximation to the physics of parallel electron motions, are a simple model that describes resistive drift wave turbulence. We present numerical analyses of bifurcation phenomena in the model that provide new insights into the interactions between turbulence and zonal flows in the tokamak plasma edge region. The simulation results show a regime where, after an initial transient, drift wave turbulence is suppressed through zonal flow generation. As a parameter controlling the strength of the turbulence is tuned, this zonal flow dominated state is rapidly destroyed and a turbulence-dominated state re-emerges. The transition is explained in terms of the Kelvin-Helmholtz stability of zonal flows. This is the first observation of an upshift of turbulence onset in the resistive drift wave system, which is analogous to the well-known Dimits shift in turbulence driven by ion temperature gradients.Comment: 21 pages, 11 figure

Turbulent Thermal Equilibration of Collisionless Magnetospheric Plasmas

How thermal equilibrium is determined in a weakly collisional plasma is a fundamental question in plasma physics. This letter shows that the turbulence driven by the magnetic curvature and density gradient tends to equilibrate the temperature between species without collisions in a magnetospheric plasma. The classical stability analysis in terms of energetic consideration reveals the interchangeable roles of electrons and ions for destabilization depending on their temperatures. Nonlinear gyrokinetic simulations confirm that the higher-temperature destabilizing species gives free energy to heat the other species to achieve the equal temperature state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let

A scenario for heart failure during the filling phase

Heart failure (HF) is a life-threating cardiac disease that develops progressively for the reduced ability of the left ventricle (LV) to pump blood into the circulation during systole. HF can also develop in patients with a preserved systolic function, typically in presence of hypertrophic cardiomyopathy (HCM). This type of HF is sometimes termed as diastolic HF, but its biomechanical origin is still unclear. This study employs a physics-based analysis of both the LV and left atrium (LA) in selected HCM patients and matched healthy subjects using 3D echocardiography and demonstrates that alteration on the LV side (stiffening) reduces the elastic recovery of the LA. Moreover, the analysis of the forces exchanged between the two chambers demonstrates that they result unbalanced, keeping the LA in a sustained stretched condition that leads to dilation. This scenario clarifies the diastolic root of the dysfunction that may likely be the cause of the spiraling of events progressing toward failure of both LA emptying and LV filling. This deeply interdisciplinary study provides a physics-based basis for both physics/engineering modeling of heart function and to cardiologists for the design of clinical studies

Gyrokinetic simulations of the tearing instability

Linear gyrokinetic simulations covering the collisional -- collisionless transitional regime of the tearing instability are performed. It is shown that the growth rate scaling with collisionality agrees well with that predicted by a two-fluid theory for a low plasma beta case in which ion kinetic dynamics are negligible. Electron wave-particle interactions (Landau damping), finite Larmor radius, and other kinetic effects invalidate the fluid theory in the collisionless regime, in which a general non-polytropic equation of state for pressure (temperature) perturbations should be considered. We also vary the ratio of the background ion to electron temperatures, and show that the scalings expected from existing calculations can be recovered, but only in the limit of very low beta.Comment: 7 pages, 10 figures, submitted to Po

Random forcing with a constant power input for two-dimensional gyrokinetic simulations

A method of random forcing with a constant power input for two-dimensional gyrokinetic turbulence simulations is developed for the study of stationary plasma turbulence. The property that the forcing term injects the energy at a constant rate enables turbulence to be set up in the desired range and energy dissipation channels to be assessed quantitatively in a statistically steady state. Using the developed method, turbulence is demonstrated in the large-scale fluid and small-scale kinetic regimes, where the theoretically predicted scaling laws are reproduced successfully.</jats:p