Gain curves and hydrodynamic simulations of ignition and burn for direct-drive fast-ignition fusion targets

Abstract

Hydrodynamic simulations of realistic high-gain fast-ignition targets are performed, including one-dimensional simulations of the implosion and two-dimensional simulations of ignition by a collimated electron beam and burn propagation. These simulations are used to generate gain curves for fast-ignition direct-drive inertial confinement fusion. The minimum energy required for ignition is computed for fast-electron beams with a monoenergetic or Maxwellian distribution, generated by a constant or Gaussian laser pulse. It is found that realistic fast-ignition targets can be ignited by monoenergetic collimated electron beams with a radius of 20μm, duration of 10ps, and energy of 15kJ. Simulations using ponderomotive temperature scaling for fast electrons and Gaussian laser pulses predict a minimum laser energy for ignition of 235kJ (105kJ) for the energy conversion efficiency from the laser to fast electrons 0.3 (0.5) and the wavelength of 1.054μm. Such large energies are required because ultra-intense lasers are predicted to generate very energetic (multi-MeV) electrons with stopping distance exceeding the target size. The fast-electron energy, the stopping distance and the minimum energy required for ignition can be reduced using frequency-doubled laser pulses. Simulations of idealized cone targets are also performed in order to determine a lower bound of the gain deterioration due to the cone.