Acceleration of impurity ions in the coulomb explosion of a relativistic spherical cluster with a complex ion compositio
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MA DYNAMICS
Acceleration of Impurity Ions in the Coulomb Explosion of a Relativistic Spherical Cluster with a Complex Ion Composition V. F. Kovaleva, c, V. Yu. Bychenkovb, c, and A. V. Andriyashc a
Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, Miusskaya pl. 4, Moscow, 125047 Russia b Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia c Dukhov AllRussia Research Institute of Automation, Moscow, 127055 Russia email: [email protected] Received May 10, 2012
Abstract—A semianalytical model of the acceleration of light impurity ions to relativistic energies in the Coulomb explosion of a spherically symmetric homogeneous microtarget (cluster) consisting of ions of two types has been proposed. The spatiotemporal and spectral characteristics of accelerated impurity ions, which have a quasimonochromatic spectrum, have been determined. The properties of highenergy impurity ions have been studied as functions of the total charge of the cluster and its ion composition. DOI: 10.1134/S1063780X12110049
1. INTRODUCTION After the appearance of femtosecond laser pulses with the intensity above 1022 W/cm2 [1], study of the socalled relativistic Coulomb explosion [2], which appears at the laser irradiation of microtargets (micro droplets), became of applied interest. Owing to the relativistic skineffect, such highintensity laser pulses can induce volume ionization, heating, and accelera tion of electrons of the target with the size sufficient for the acceleration of the ions of the formed expand ing charged plasma to relativistic energies. This is a qualitative difference from the wellstudied Coulomb explosion of the ion core of a usual small cluster [3–6]. For example, in the case of ions of one type, their rel ativism is manifested in the formation of the shell structure of an exploded spherical target [2] in contrast to the standard expansion of a plasma ball into vacuum corresponding to usual spreading of matter. At a fairly high intensity of a femtosecond laser pulse, the characteristic energy ε of ions of the exploded cluster is independent of the laser intensity and is determined by the Coulomb energy of the tar get, i.e., by its total charge Q; the corresponding con dition under which an ion with the mass M and charge ei of the spherical target with the radius r0 becomes rel ativistic owing to the Coulomb explosion has the form ei Q / Mc 2r0 ⱜ 1. The Coulomb explosion of the quasi uniform spherical target consisting of light and heavy ions is of particular interest [7]. Light ions in this expanding target are faster and these ions, initially dis tributed uniformly, are displaced to the periphery of the target and are efficiently accelerated by the Cou lomb field of the following heavy ions. These heavy ions, acting as a Coulomb piston, promote the forma
tion of a pronounced bunch (in the form of a shell) of almost monoenergetic light ions similar to those pre dicted for the Coulomb explosion of spherical clusters with the shell of li
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