Prepulse effects on the generation of high energy electrons in fast ignition scheme

Abstract

The energy distribution of the produced high energy electrons in the interaction of ultraintense picosecond laser pulses with high-Z solid targets is shown to be sensitive to the preformed plasma created by the prepulse and the amplified spontaneous emission pedestal. The created preformed plasmas, which are obtained by radiation hydrodynamic simulations for the present heating laser system at ILE, Osaka University, are seen to extend up to 30–100 μm just before the arrival of the main pulse. The dependences of the coupling efficiency of the laser energy to high energy electrons, and the energy spectra of these accelerated electrons, on this preformed plasma, are studied via a two-dimensional particle-in-cell simulation code. It is found that in a small preformed plasma case, J×B heating is dominant and the produced electron temperature agrees well with Haines’ scaling law [Haines et al., Phys. Rev. Lett., 102, 045008 (2009)]. While in a large preformed plasma case, in addition to J×B heating and/or vacuum heating, other acceleration mechanisms, such as stochastic heating, can accelerate electrons to very high energies, carrying a significant fraction of input laser energy. Even after several picoseconds, the number of high energy electrons (0.5 MeV<E<5 MeV) generated in a small preformed plasma case can be several times larger than that of a large preformed plasma case.

Generation and optimization of electron currents along the walls of a conical target for fast ignition

“…36 However, the power law dependence might not be due to the target geometry. Although further investigations are required, the spectrum obtained for the narrow spot size, as well as recently published results, 41 seems to indicate that a power law function up to a few MeV could also be observed for flat foil targets at these intensities.…”

Laser-driven collimated tens-GeV monoenergetic protons from mass-limited target plus preformed channel

“…In order to model ASE and prepulse effects, we use a preplasma density profile obtained from hydrodynamic simulations. 33 Typically, the preplasma in the moderately overdense region has a density scale length L ¼ 1k. Compared to the L ¼ 0 case, more laser energy is depleted in laser-foil interaction stage, so that the pump depletion length is reduced.…”

Efficient multi-keV X-ray generation from high-contrast laser plasma interaction

“…A two stage sharp preplasma is formed by the high contrast, high irradiance laser pulse. This two stage preplasma is possible to enhance the laser absorption and transfer efficiency [4], and results an enhancement of K x-ray yield.…”

“…Numerous studies have investigated the physics of hot electron generation and laser absorption. Both factors are critically affected by the formation of pre-plasma generated by a leakage pre-pulse from the laser system [3,4]. Consequently, the K yield is substantially affected by pre-plasma formation [5].…”