39 / 2020-02-11 09:41:13

Transport of ultraintense laser-driven relativistic electrons in dielectric targets

Field ionization; collisional ionization; ultraintense laser; dielectric target.

全体主题 > 激光和粒子束聚变

Transport of high-current relativistic electron beams driven by ultra-intense laser interactions with plasmas is relevant to many applications of high energy density physics, particularly in the areas of the fast ignition scheme of inertial confinement fusion, laser-driven ion acceleration, and production of ultrashort radiation sources. A target can be ionized by relativistic electrons both through field ionization and collisional ionization, inducing nonlinear and collective effects that can feed back to the transport of the relativistic electrons. It is important to comprehensively investigate the transport process of the relativistic electrons in such target, especially in insulators that are without free electrons initially.
However, the transport of relativistic electrons in solid targets has not been understood well yet, especially in the dielectric target. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electrons transport in a silicon target by including the field ionization and collisional ionization process. An ionization wave is found propagating in the insulator, with a velocity dependent on the laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. A two-stream instability behind the ionization front arises for the cases with laser intensity greater than 5×10^19 W/cm^2 that produce high relativistic electron current densities. The results are useful to the applications related to laser-driven relativistic electrons transport in dielectric target, such as fast ignition and laser-driven ion accelerations.