Abstract
Abstract Stochastic heating is a generic mechanism in the production of energetic electrons during the interaction of intense short laser pulse with under-dense plasma. In this paper, we employ fully kinetic 1D-3 V particle-in-cell (PIC) simulations to examine the effects of the pulse shape in the performance of the stochastic heating. To correctly characterize the local plasma temperature, we exploit the proper (relativistically invariant) stress tensor, P i j , which decouples the bulk motion from stochastic fluctuations. Our results reveal a strong dependence of heating performance on the pulse shape parameter. It is represented that the pulse rise-time is one of the main factors affecting the type of heating mechanism of electrons. In this regard, the possibility of stochastic heating is confirmed in the smooth shape pulse. It is shown that unlike the pulses with quickly rising time, when the pulse rise-time is initially smooth, Raman backscattered fields can act as a second counter-propagating wave and provide the necessary condition for the stochastic heating. In these pulses, the stochastic heating threshold time is dependent on the pulse rise-time. So that, decreasing the pulse rise-time, down to a definite value, leads to the stronger initiation of the backward Raman scattering, whence, faster onset of the stochastic heating.
Published Version
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