It is shown that inertial confinement fusion targets designed with low implosion velocities can be shock-ignited using laser-plasma interaction generated hot electrons (hot-e's) to obtain high energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-e's which can be produced only at a large laser facility like the National Ignition Facility, with the laser-to-hot-e conversion efficiency greater than 10% at laser intensities ∼10^{16}  W/cm^{2}.

In atmospheric radio frequency discharges at 13.56 MHz, with the electrode gap reduced, the sheath region eventually occupies a main portion of the electrode spacing and the bulk plasma region is significantly compressed. The computational results in this letter based on a one-dimensional fluid model show that by increasing the excitation frequency over 13.56 MHz, the traditional glow-plasma structure could gradually recover even at very small sizes with a well defined quasineutral plasma region, and the electron density is improved but the electric fields in sheath region are reduced. This study indicates that the excitation frequency can be used to modulate the discharge structure and then tailor the plasma-surface interaction in atmospheric microplasmas.Atmospheric microplasmas have commanded much attention in recent years due to the considerable scientific depth and potential applications. 1-4 For atmospheric capacitively radio-frequency (rf) discharges, when the electrode gaps are confined to submillimeter dimensions, the generated microplasmas show many unique properties compared to the large-scale atmospheric plasmas, 3 such as the high energetic electrons, 5 different discharge structures, 6,7 and nonequilibrium characters. 8 The experimental 6 and computational studies 5,7 have demonstrated that in atmospheric rf discharges at 13.56 MHz, with the electrode gap reduced, the traditional glow-plasma (GP) structure will eventually transit to a new sheath-dominated-plasma (SDP) structure, where the sheath region occupies a large portion of the electrode gap and almost no distinct bulk plasma region develops. In a SDP structure, three electron groups with different electron temperatures have been revealed by the Particle-In-Cell (PIC) simulation and the high energetic electrons present a new way to interact with the electrodes or the given surfaces, moreover these electrons maybe contribute to the reactivity of atmospheric microplasmas. 5 The discharge modes in rf microplasmas have been discussed but still need to be further clarified by experiments and simulations. 5-7 Increasing frequency is widely accepted as a way to enhance the discharge stability and reduce the electron temperature at a constant power density. 10-12 Nevertheless, the frequency effects on the structure transition in atmospheric rf discharges are largely unexplored. Although the microplasmas in SDP regime show many advantages and the GP structure with quasineutral plasmas may still be very useful in many applications at very small sizes. The experimental diagnosis of atmospheric microplasmas, however, is facing many new challenges due to the small dimension and high gas pressure, 3,4 and numerical simulations provide a valuable alternative for investigating the properties of microplasmas. 2In this letter a one-dimensional fluid model is explored to study the transition of discharge structures in capacitively rf discharges at atmospheric pressure. 11,12 Briefly, the continuity equations with the drift-diffusion approximation are used to des...

X-ray emission from laser-plasma interaction is an important x-ray source, and improving laser to x-ray conversion is imperative for various applications. The laser to x-ray conversion efficiency (CE) was simulated for gold targets with different initial densities. Using a 0.1 g/cm3 Au layer target, an x-ray conversion efficiency of 50.8% was obtained, which was 1.34 times of the 37.9% for the solid density target. It has been shown that the enhancement of the x-ray conversion efficiency is caused by the increase of absorption from the incident laser and reduction of ion kinetic energy due to the initial low density of the gold target.

Experiments were performed with CH, Be, C, and SiO2 ablators interacting with high-intensity UV laser radiation (5 × 1015 W/cm2, λ = 351 nm) to determine the optimum material for hot-electron production and strong-shock generation. Significantly more hot electrons are produced in CH (up to ∼13% instantaneous conversion efficiency), while the amount is a factor of ∼2 to 3 lower in the other ablators. A larger hot-electron fraction is correlated with a higher effective ablation pressure. The higher conversion efficiency in CH is attributed to stronger damping of ion-acoustic waves because of the presence of light H ions.