The Generation of Collimated Moderate Temperature Electron Beam in Shock Ignition Relevant Experiments on OMEGA Lasers*

Understanding of laser-plasma instabilities (LPI) and the resultant hot electrons are critical for the design of the shock ignition (SI). We have conducted a series of experiments on OMEGA-EP and OMEGA-60 to characterize the hot electrons and signatures of LPI from the interaction of the kilo-joule infrared (IR) and ultraviolet (UV) lasers with long-scalelength keV plasmas at SI-relevant peak laser intensities (10¹⁶ W/cm²). The hot electrons were found to have temperatures in the range of 45 – 90 keV with 2.0 – 3.5% energy conversion efficiency. The hot electron beam divergence is less than 22˚, which is indicated by the size of the Cu K-alpha spot. The fraction of the high energy hot electrons (> 120 keV) has also been quantified. The time-resolved spectrum of the SRS light shows pump depletion in the low-density plasma (0.01 n_c– 0.20 n_c) during the first 0.5 ns of the UV spike pulse. The observed directional and moderate temperature hot electrons are encouraging for the electron-assisted SI. Details of the experiments and comparisons with the PIC simulations will be presented.