Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. Here we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the current sheet in this regime is several electron mean-free paths. These results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.

Figure 1

The coefficients as functions of $\mathrm{\Omega }\tau$ in the dimensionless analysis of the GOL.

Figure 2

The temperature profile (normalized to $T_{e0}$) and the magnetic flux contours at $t=10\tau$ (a) and $t=120\tau$ (b). ${\lambda }_{\mathrm{mfp}}$ is the mean-free path calculated from initial density and temperature.

Figure 3

Contributions to the GOL for a cut across the reconnection layer near $x=0$ for (a) before reconnection ($t=10\tau$) and (b) during steady reconnection ($t=120\tau$). The red line is $E_y$ obtained from PIC simulation, and the black line shows the sum of the terms on the various contributing terms. $E$ fields are measured in terms of $B_0{v}_{th0}$, where $B_0$ is the initial peak magnetic field in the simulation and $v_{\mathrm{th}0}=\sqrt{T_{e0}/m_e}$.

Figure 4

(a) Profiles of $q,j$ and $B$ in a cut across the reconnection layer near $x=0$ at $t=120\tau$. (b) ${\mathrm{\Pi }}_{yz}$ obtained from the PIC simulation, calculated from PFV and HFV using the quantities in the above plot, and a smoothed result applying the nonlocal kernel of Eq. (9).