Electrons In Laser-produced Plasmas Research Articles

Ion acoustic turbulence driven by return current leads to hot electrons in laser-produced plasma

The instability of ion acoustic waves due to the return current driven by an electron heat flux is a source of ion acoustic turbulence (IAT), which provides electromagnetic wave conversion into Langmuir waves at a near-critical density in inertial confinement fusion plasmas. The Langmuir waves triggered by IAT produce hot electrons. We formulate a theoretical model of hot-electron generation by these Langmuir waves and analyze it qualitatively. We show that IAT-driven hot electrons are generated in the backward direction and, therefore, preheat the target core because of the electron refluxing in the coronal plasma back toward the solid target.

Kinetic magnetization by fast electrons in laser-produced plasmas at sub-relativistic intensities

The problem of spontaneous magnetic field generation with nanosecond laser pulses raises a series of fundamental questions, including the intrinsic magnetization mechanisms in laser-driven plasmas and the understanding of charge-discharge processes in the irradiated target. These two issues are tightly bound as the charge-discharge processes are defined by the currents, which have in turn a feedback by magnetic fields in the plasma. Using direct polaro-interferometric measurements and theoretical analysis, we show that at parameters related to the PALS laser system (1.315 μm, 350 ps, and 1016 W/cm2), fast electrons play a decisive role in the generation of magnetic fields in the laser-driven plasma. Spatial distributions of electric currents were calculated from the measured magnetic field and plasma density distributions. The obtained results revealed the characteristics of strong currents observed in capacitor-coil magnetic generation schemes and open a new approach to fundamental studies related to magnetized plasmas.

Hybrid Two-Dimensional Electron Transport in Self-Consistent Electromagnetic Fields

The paper outlines features of the implicit hybrid simulation code ANTHEM, which uniquely provides histories for the transport and deposition of suprathermal and thermal electrons in laserproduced plasmas. The code models two-dimensional electron transport through steep density gradients and across contiguous collisional and collisionless target regions with the plasma dynamics dominated by self-consistent E and B fields. ANTHEM employs separate Eulerian fluid ion and thermal electron treatments and models suprathermal electrons as either a third fluid or as a set of collisional particle-in-cell (PIC) particles. We outline new techniques required to obtain implicit electromagnetic fields in two spatial dimensions permitting time steps well in excess of the local plasma period. A new implicit scattering model is discussed. The utility of our approach is demonstrated with sample applications to collisional surface transport on foil targets.

Calculation of X-ray bremsstrahlung and characteristic line emission produced by a Maxwellian electron distribution

Using power-law least-squares fits to thick-target measurements of X-ray bremsstrahlung and characteristic line emission, analytic expressions for spectra and emission efficiencies of X-rays produced by a Maxwellian electron distribution were calculated. These expressions are particularly useful for the analysis of X-ray spectra produced by hot electrons in laser-produced plasma. The effect of self-absorption on the analysis of these spectra is estimated. It is shown that both the spectral shape and the adsorption effects dictate that bremsstrahlung measurements of plasma temperature should be made at photon energies greater than kT.

Estimation of temperature and fraction of superthermal electrons in laser-produced plasmas

A simple method for the estimation of temperature and fraction of superthermal electrons in laser-produced plasmas is discussed.

Double-Diffusion Hot-Electron Transport in Self-ConsistentEandBFields

A two-component, flux-limited diffusion model is introduced for the self-consistent transport of hot electrons in laser-produced plasmas. Megagauss fields from the $\ensuremath{\nabla}{n}_{h}\ifmmode\times\else\texttimes\fi{}\ensuremath{\nabla}{n}_{c}$ source are predicted for $I{\ensuremath{\lambda}}^{2}\ensuremath{\gtrsim}3\ifmmode\times\else\texttimes\fi{}{10}^{16}$ W \ensuremath{\mu}${\mathrm{m}}^{2}$/${\mathrm{cm}}^{2}$. For low-$Z$ target materials a prompt back-side $B$ field is a signature for hot electrons reaching the back of thin foils.