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Electron energy spectrum in the field‐ionized plasma
Author(s) -
Khalilzadeh E.,
Chakhmachi A.,
Dehghani Z.,
Rezaei S.,
Jafari M. J.
Publication year - 2021
Publication title -
contributions to plasma physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0863-1042
DOI - 10.1002/ctpp.202000219
Subject(s) - atomic physics , ionization , plasma , electron , physics , electric field , population , ion , quantum mechanics , demography , sociology
Abstract In this article, the effect of ionization on the energy spectrum of electrons within the interaction of a laser pulse with hydrogen atoms is investigated using particle‐in‐cell simulation codes. The results show that the behaviour of electrons' energy distribution function in the field‐ionized plasma, which occurred due to the field ionization, compared with that in the pre‐plasma strongly depends on the pulse shape. For short rise‐time pulses (here 30 fs), due to the rapid enhancement of laser electric field, ionization occurs quickly, and as a result, there is not much difference in the electron energy in both the media. However, for pulses with rise time of 40 fs, in the pre‐plasma state, the electron population reaches higher energies compared with the field‐ionized plasma state. The main reason for this difference is the nonlinear wave breaking that happens earlier due to density inhomogeneity in the field‐ionized plasma. On the other hand, at longer rise‐time pulses (here 60 and 70 fs), electrons achieve higher energies in the field‐ionized plasma than those in the case of pre‐plasma. In this case, because of density fluctuations in the field‐ionized plasma, the Raman backscattered radiations are seeded by a strong initial noise at the earlier times and the Mendonca condition for chaos threshold is met sooner. Therefore, the electrons gain more energy through the stochastic mechanism that is in agreement with chaotic nature of the motion.