Ion beam fusion plasma. Ablation and heating regimes

The one-dimensional self-similar motion generated by an intense ion beam pulse, of energy per nucleon E b =E 0 (t/ tau ) 2/3 and current intensity per unit area I b =I 0 (t/ tau ) 1/3 (0<or=t<or= tau ), impinging on an initially cold half-space plasma of electron density n 0 is considered; the resulting motion is governed by two dimensionless numbers alpha approximately n 0 2 tau 3 I 0 /E 0 5 and beta approximately E 0 /(I 0 tau ) 1/2 which contain the basic beam and plasma parameters. Detailed asymptotic results have been obtained for alpha large and small. For alpha >>1 results show that there exists a well defined ablation surface separating an isentropic compression region from a much wider expansion flow where the beam energy absorption occurs; the ablation pressure and the ablated plasma flow rate as a function of the beam parameters are found from the analysis; the efficiency of the acceleration of thin foils have been also calculated. For alpha <<1, the analysis shows the existence of a rarefaction wave that separates a heating region (where plasma convection is negligible) developing into the undisturbed plasma from a much thinner expansion flow region. Profiles of beam velocity, density and temperature, through the entire motion have been obtained.