Anomalous Resistivity Resulting from MeV-Electron Transport in Overdense Plasma

Laser produced hot electron transport in an overdense plasma is studied by three-dimensional particle-in-cell simulations. Hot electron currents into the plasma generate neutralizing return currents in the cold plasma electrons, leading to a configuration which is unstable to electromagnetic Weibel and tearing instabilities. The resulting current filaments self-organize through a coalescence process finally settling into a single global current channel. The plasma return current experiences a strong anomalous resistivity due to diffusive flow of cold electrons in the magnetic perturbations. The resulting electrostatic field leads to an anomalously rapid stopping of fast MeV electrons (almost 3 orders of magnitude stronger than that through classical collisional effects).

Figure 1

Transverse cut of $|E_{\perp }|$ at $t=4\tau$ (a) and $|B_{\perp }|$ at $t=5$ (b), $15$ (c), $25$ (d). Each plot is observed at $X=2.85\lambda$.

Figure 2

The longitudinal cut at the center of the hot electron current (a) and the return current (b) at $t=13\tau$. The longitudinal current profile integrated over the transverse region at $t=16\tau$ (c). The longitudinal profile of $⟨|B|⟩$ and $⟨E_x⟩$ at $t=16\tau$ (d). Those fields are normalized by the laser field, $B_{z0}$ and $E_{y0}$, respectively, e.g., $E_x=0.005\sim 30\mathrm{k}\mathrm{e}\mathrm{V}/\mu \mathrm{m}$.

Figure 3

The time evolution of electron energy spectra observed at around $X=10.6\lambda$ (a) and $X=3.7\lambda$ (b). Contour lines indicate common logarithms of the number of electrons.

Figure 4

The time evolution of the Lyapunov exponent $\lambda$. The phase plots $P_y-P_z$ of the particle which start with a negative $P_x$ (a) and the positive $P_x$ (a′) are overplotted. The dotted line in the phase plots indicates the perturbed orbit.

Figure 5

The stopping range $\rho R$ (solid line) and the hot electron temperature $T_h$ (broken line) versus the plasma density in the case of the transverse uniform laser with $a=3.75$. These plots are evaluated after the global magnetic structures reach almost a steady state.