A first analysis of fast ignition of precompressed ICF fuel by laser-accelerated protons

Abstract

The main parameters of the beam required to ignite a precompressed DT fuel, as foreseen by the recently proposed scheme of fast ignition by laser-accelerated protons (Roth et al 2001 Phys. Rev. Lett. 86 436), are studied by 2-D numerical simulations and a simple model. For simplicity, instantaneous proton generation at distance d from the compressed fuel and exponential proton energy spectrum, dn/dε∝exp (-ε/Tp), are assumed. An analytical expression and parametric numerical results are then given for the dependence of the minimum required beam energy on d, Tp and on the fuel density ρ. For the parameters of Roth et al (d≈4 mm; ρ≈400 g/cm3) the minimum total proton energy for ignition is about 40 kJ.

Ion beam requirements for fast ignition of inertial fusion targets

“…Atzeni et al [19] reported for this target a minimum ignition energy of 8.5 kJ. Our calculations show the same ignition energy when the ion scattering is off, while it increases slightly to 8.75 kJ for the FP energy deposition model.…”

“…8 that the beams have a penetration into the dense core around 1.5 gcm −2 , and slightly higher for the quasi-monoenergetic ions. These values are higher than the optimal value of 1.2 gcm −2 [19,51] due to the energy deposition in the coronal plasma. The coupling efficiencies, defined as the energy deposited in the DT at densities higher than 200 gcm −3 , for the perfectly collimated beams are 0.58 for the maxwellian proton and carbon beams, and 0.70 for the quasi-monoenergetic carbon ions, similar to those reported in Refs.…”

“…For low temperatures, ions do not penetrate enough in the target to deposit a significant fraction of their energy into the dense core, raising the ignition energies. For high temperatures, ions penetrate into the core more than the optimal areal density of 1.2 gcm −2 [19] raising again the ignition energies due to the increase of the DT mass heated by the beam.…”

“…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.…”

Status and Prospects of the Fast Ignition Inertial Fusion Concept

“…Power law fits to the numerical data have given useful scaling laws for the hot spot parameters, for example the hot spot energy requirement E/1kJ= 140(ρ /100gcm -3 ) -1.8 . Modeling specific to proton ignition has also been carried out 11 and adds consideration of transit time spread, and optimum proton energies in the plasma jet.…”