Design of a Peanut Hohlraum with Low Gas-Fill Density for the Laser Megajoule

Recent experiments on the National Ignition Facility [D.E. Hinkel et al., Phys. Rev. Lett. 117, 225002 (2016)] demonstrates that utilizing a long, large case-to-capsule ratio (=3) conventional cylindrical hohlraum at moderate gas-fill density (=0.6 mg/cm3 4He) improves the drive symmetry controaums has a little chance to achieve ignition at an acceptable energy level due to its small margin for the laser cone propagation. In this letter, a noncylindrical hohlraum, called as peanut hohlraum, using a larger case-to-capsule (=3.46) at lower gas-fill density (=0.3 mg/cm3 4He) is proposed to ignite a high-foot pusher capsule with a shorter pulse (~9ns). The peanut hohlraum requires about 2.5 MJ laser energy to achieve 306 eV peak drive temperature while the low-z plasma electron density on the inner cone path is maintained very low which results in little simulated Raman backscattering and the high-z bubble still stays away from the inner cone path without the laser absorption in it, which favor the drive symmetry control. Crossed-beam energy transfer is also neglectable because the crossing position is far away from the LEH. The peanut hohlraum can provide a good drive environment for capsule to achieve ignition, so it is undoubted that it will add to the diversity of ICF approaches.