On the basis of one-dimensional coupled PIC and Fokker–Planck simulations, the core heating properties of different cone materials for sub-ignition class experiments of the cone-guiding fast ignition have been studied. When Au is used as a material of the cone tip, the Au atoms ionize to a high charge state during the interaction with a heating pulse in a few hundreds of femtoseconds. Because of the extreme photon pressure, the pulse starts to interact directly with a solid-density cone tip after the density slope is steepened. In addition, the electrons in the return current are strongly scattered by the highly ionized Au ions. In such a situation, the energy coupling of the heating laser to the fast electrons could drop drastically. During the transport in the cone tip, the quality of the generated fast electron beam deteriorates due to the collisional and resistive drags and the scattering by the Au ions. As a result, the core heating gets saturated quickly and the energy coupling efficiency of the heating laser to the core decreases. We proposed CH as an alternative material of cone tip to reduce the collisional defects. It is found that in comparison with the Au cone tip, a twice higher rise in temperature of a compressed CD core has been achieved with the CH cone tip after 1 ps heating by a 1020 W cm−2 intensity pulse.
Fast ignition integrated experiments and high-gain point design