Novel Mechanism to Generate Suprathermal Electrons by Anti-Stokes Langmuir Decay Instability Cascade *

Here, a new mechanism for electron acceleration by anti-Stokes Langmuir decay instability cascade of forward stimulated Raman scattering is proposed. The problem is divided into three regions. When the electron temperature is T_e = 2.5 keV, the first region is between densities of n_e < 0.108n_c (Region I). Here, the backward stimulated Raman scattering of forward stimulated Raman scattering and corresponding Langmuir decay instability accelerate the electrons to high energy. The second region is when the densities are between 0.108n_c < n_e < 0.138n_c (Region II). Here, anomalous hot electrons with kinetic energies above 100 keV are also generated. This process cannot be explained by traditional acceleration mechanisms. Evidence is presented to show that these hot electrons arise from anti-Stokes process of Langmuir decay instability cascade of forward stimulated Raman scattering. Finally, the third region is n_e > 0.138n_c (Region III), where the electrons trapped by backward stimulated Raman scattering induced Langmuir wave are accelerated by the forward stimulated Raman scattering induced Langmuir wave directly. This new mechanism not only explains anomalous energetic electron generation in indirectly driven inertial confinement fusion experiments and the significant energy losses on the inner cones of beams for the first time (compensated by cross-beam energy transfer at the laser entrance holes of the holhraum targets), but also provides a new way of accelerating the electrons to higher energy in the laser-driven wakefield accelerator research.