Numerical study of fast ignition of ablatively imploded deuterium–tritium fusion capsules by ultra-intense proton beams

Abstract

Compression and ignition of deuterium-tritium fuel under conditions relevant to the scheme of fast ignition by laser generated proton beams ͓Roth et al., Phys. Rev. Lett. 86, 436 ͑2001͔͒ are studied by numerical simulation. Compression of a fuel containing spherical capsule driven by a pulse of thermal radiation is studied by a one-dimensional radiation hydrodynamics code. Irradiation of the compressed fuel by an intense proton beam, generated by a target at distance d from the capsule center, and subsequent ignition and burn are simulated by a two-dimensional code. A robust capsule, absorbing 635 kJ of 210 eV ͑peak͒ thermal x rays, with fusion yield of almost 500 MJ, has been designed, which could allow for target gain of 200. On the other hand, for a reasonable proton spectrum the required proton beam energy E ig , exceeds 25 kJ ͑for dϭ4 mm͒, even neglecting beam losses in the hohlraum and assuming that the beam can be focused on a spot with radius of 10 m. The effects of proton range lengthening due to the increasing plasma temperature and of beam temporal spread caused by velocity dispersion are discussed. Ways to reduce E ig to about 10 kJ are discussed and analyzed by simulations.

Ion beam requirements for fast ignition of inertial fusion targets

“…This formula predicts range lengthening when plasma electron velocities are comparable or higher than the fast ion velocity. Range lengthening is important for protons with maxwellian energy distributions generated away from the DT because it balances the reduction of the ion kinetic energy on target due to time spread, keeping the ion range almost constant during the ion pulse [20]. It is worth noting that the range lengthening in the temperature range 0.1 − 10 keV is substantially lower for ions heavier than protons, as shown in Fig.…”

“…It allows us to include any ion initial distribution function and the scattering due to ion-ion collisions, neglected in the standard ion tracking schemes [20]. The FP equation is solved in 3D settings by using a Monte Carlo method similar to that used in our hybrid code for fast electron transport calculations [37].…”

“…All beams have an energy of 10 kJ and are generated at a distance to the simulation box d = 500 µm. The power on target p(t) of an ion beam generated instantaneously in a foil placed at a distance d is given by the formula [20]:…”

“…This was followed by theoretical studies on the TNSA scheme [16,17], target studies [18][19][20][21], new irradiation schemes [9,11,12] and the use of ions heavier than protons [22,23]. Other schemes such as the two-pulse scheme described in Ref.…”

High-quality proton bunch from laser interaction with a gas-filled cone target

“…Such energetic ions can be promising for many scientific or societal applications, such as proton radiography [1], fast ignition for inertial confined fusion [2][3][4], or hadron-therapy [5]. For most of these applications, ion beams with high energy, low energy spread and high collimation are required.…”