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A new self-similar solution is presented which describes nonrelativistic expansion of a finite plasma mass into vacuum with a full account of charge separation effects. The solution exists only when the ratio Λ=R∕λD of the plasma scale length R to the Debye length λD is invariant, i.e., under the condition Te(t)∝[ne(t)]1−2∕ν, where ν=1, 2, and 3 corresponds, respectively, to the planar, cylindrical, and spherical geometries. For Λ⪢1 the position of the ion front and the maximum energy Ei,max of accelerated ions are calculated analytically: in particular, for ν=3 one finds Ei,max=2ZTe0W(Λ2∕2), where Te0 is the initial electron temperature, Z is the ion charge, and W is the Lambert W function. It is argued that, when properly formulated, the results for Ei,max can be applied more generally than the self-similar solution itself. Generalization to a two-temperature electron system reveals the conditions under which the high-energy tail of accelerated ions is determined solely by the hot-electron population.

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Abstract. Ignition conditions in axially magnetized cylindrical targets are investigated by examining the thermal balance of assembled DT fuel configurations at stagnation. Special care is taken to adequately evaluate the energy fraction of 3.5 MeV alpha particles deposited in magnetized DT cylinders. A detailed analysis of the ignition boundaries in the ρR, T parametric plane is presented. It is shown that the fuel magnetization allows a significant reduction of the ρR ignition threshold only when the condition BR ² 6 × 10 5 G cm is fulfilled (B is the magnetic field strength and R is the fuel radius).

The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the α-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain. However, measurements of ion stopping in plasmas are scarce and mostly restricted to high ion velocities where theory agrees with the data. Here, we report experimental data at low projectile velocities near the Bragg peak, where the stopping force reaches its maximum. This parameter range features the largest theoretical uncertainties and conclusive data are missing until today. The precision of our measurements, combined with a reliable knowledge of the plasma parameters, allows to disprove several standard models for the stopping power for beam velocities typically encountered in inertial fusion. On the other hand, our data support theories that include a detailed treatment of strong ion-electron collisions.

[1] An analytical model describing the combined effect of mass accomodation and net adsorption of trace gases on the surfaces of growing ice particles (trapping) is developed. An approximate solution for the release of trapped trace gases from evaporating ice particles is also given. The model fully accounts for the fact that atmospheric ice particles frequently experience substantial subsaturations and supersaturations. In such situations, pure adsorption models cannot be employed to calculate the trace gas uptake. Limiting cases are discussed in which uptake is solely controlled by gas diffusion (burial limit) or by surface kinetics (adsorption limit). The model results are expressed in terms of a nonreactive uptake coefficient for use in atmospheric models. Crucial factors controlling trapping are the rate of desorption (or net molecular escape rate) and the ice growth rate. Trace gase molecules can be effectively trapped in bulk ice even at low ice supersaturations when their times of adsorption are sufficiently long. The trapping model may help provide physically sound interpretations of field and laboratory measurements of trace gas uptake on growing ice surfaces. Previous global model studies of nitric acid uptake in cirrus clouds only considering adsorption likely underestimated the resulting dentrification, because the vertical redistribution is driven by the largest ice crystals which trap nitric acid most efficiently.

The effect of strong thermal radiation on the structure of quasi-stationary laser ablation fronts is investigated under the assumption that all the laser flux is absorbed at the critical surface. Special attention is paid to adequate formulation of the boundary-value problem for a steady-state planar ablation flow. The dependence of the laser-to-x-ray conversion efficiency / r on the laser intensity I L and wavelength k L is analyzed within the non-equilibrium diffusion approximation for radiation transfer. The scaling of the main ablation parameters with I L and k L in the strongly radiative regime 1 À / r ( 1 is derived. It is demonstrated that strongly radiating ablation fronts develop a characteristic extended cushion of "radiation-soaked" plasma between the condensed ablated material and the critical surface, which can efficiently suppress perturbations from the instabilities at the critical surface. V C 2015 AIP Publishing LLC. [http://dx.