Electromagnetic field growth triggering super-ponderomotive electron acceleration during multi-picosecond laser-plasma interaction

Abstract

The dependence of the mean kinetic energy of laser-accelerated relativistic electrons (REs) on the laser intensity, so-called ponderomotive scaling, explains well the experimental results to date; however, this scaling is no longer applicable to multi-picosecond (multi-ps) laser experiments. Here, the production of REs was experimentally investigated via multi-ps relativistic laser-plasma-interaction (LPI). The lower slope temperature shows little dependence on the pulse duration and is close to the ponderomotive scaling value, while the higher slope temperature appears to be affected by the pulse duration. The higher slope temperature is far beyond the ponderomotive scaling value, which indicates super-ponderomotive REs (SP-REs). Simulation and experimental evidence are provided to indicate that the SP-REs are produced by LPI in an under-critical plasma, where a large quasi-static electromagnetic field grows rapidly after a threshold timing during multi-ps LPI.

Recent progress of laboratory astrophysics with intense lasers

“…Power law spectra of electron energy have also been observed in LFEX experiment in Osaka [56] . In Fig.…”

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“…In addition, the EM waves have random phase because of filamentation instability, sug-Figure 21. Electron distribution function obtained in LFEX experiment at Osaka (courtesy of S.Kojima) [56] .…”

“…The data are taken by Japanese X-ray satellite GINGA [9] . The hard X-ray of 16-28 keV stems from the nuclear decay of 56 Ni predicted to be generated near the center of SN1987A. As the optical thickness of the outer layer is thick and decreases as the matter expands, it is predicted to take about 1 year to be observed in the onedimensional explosion simulation as plotted with the dashed line.…”

“…However, GINGA satellite began to observe the X-ray about 100 days after the explosion. Scientists considered that the explosion is hydrodynamically unstable and the mixing of inside and outside materials conveys the central 56 Ni outer region relatively optically thin. Therefore, the effect of Rayleigh-Taylor instability is modeled in one-dimensional code to see the X-ray signal and it was found that the uniform mixing plus clumpy spike-bubble model can explain the data indicated as the solid line, not by uniform mixing.…”