Speaker
Description
The heat flux of electrons plays a crucial role in energy transport processes in collisionless or weakly collisional plasma of the solar wind. Early observations indicated that the collisional Spitzer-Härm law cannot describe the heat flux in the solar wind. Various mechanisms for regulating heat flux in the solar wind have been proposed, such as the interaction of electrons with whistler waves generated by the so-called whistler heat flux instability (WHFI). This instability arises in plasma with at least two counter-streaming electron populations. Recent observations have demonstrated the development of WHFI in the solar wind, showing that this instability generates predominantly quasi-parallel whistler waves with amplitudes up to a few percent of the background magnetic field. However, the question of whether such whistler waves can regulate the heat flux remained open.
We present the results of simulations of whistler wave generation and the nonlinear evolution of WHFI using the TRISTAN-MP PIC code. This code simulates the self-consistent dynamics of two counter-streaming electron populations: warm (core) electrons and hot (halo) electrons. We investigated wave generation in two cases: for pure WHFI, when both populations are isotropic, and for anisotropic WHFI, when halo electrons have perpendicular temperature anisotropy. Our calculations show that the instability produces whistler-mode waves propagating both parallel (anti-sunward) and anti-parallel (sunward) to the electron heat flux. The saturated amplitudes of both sunward and anti-sunward whistler waves are strongly correlated with their initial linear growth rates. We also studied spectral properties of the generated waves and demonstrated that the instability develops in quasi-linear regime. As far as the heat flux is concerned, we found that parallel and anti-parallel waves affect it in the opposite directions, but the net effect is a heat flux reduction. Our simulations indicate that while pure WHFI cannot regulate the heat flux in the solar wind, a combined heat flux and anisotropy instability can contribute to the heat flux regulation.
Acknowledgments:
The work was supported by NASA grants HGI 80NSSC21K0581 and HSR 80NSSC23K0100. We would like to acknowledge high-performance computing support from Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR's Computational and Information Systems Laboratory, sponsored by NSF grant No. 1502923.
