INFLUENCE OF AXIAL MAGNETIC FIELD TRAP ON LASER-GENERATED PLASMA L. Torrisi 1,2 , D. Margarone 1,2 , S. Gammino 2 and L. Andò 2 1 Dip.to di Fisica, Università di Messina, Ctr. Papardo 31, 98166 S. Agata, Messina, Italy 2 INFN-Laboratori Nazionali del Sud, Via S. Sofia 44, 95124 Catania, Italy Abstract - In vacuum plasma generated by laser ablation of metallic targets (Cu and Ta) was investigated with and without the influence of 0.1 T axial magnetic field. The laser beam intensity, of the order of 10 10 W/cm 2 , was obtained by a Nd:Yag operating at 1064 nm wavelength, 9 ns pulse width and 500 mJ pulse energy. Time-of-flight measurements of ion emission were performed along the direction normal to the target surface by using an ion collector. Results demonstrated that the magnetic field creates an electron trap in front of the target. The electron charge density inside the trap modifies the electric potentials in the plasma inducing an higher ion acceleration. The presence of the electron cloud not only focuses the ion beam but also increases its energy, mean charge state and current. Introduction - Laser-generated plasma in vacuum are characterized by high temperature and density, high charge state and high ion energies along the expanding direction, i.e. orthogonally to the ablated target surface. Measurements with an ion energy analyser demonstrate that the distributions follow a “Coulomb-Boltzmann-shifted” function, as reported in previous experiments [1]. Increasing the charge state the ion kinetic energy increases, due to an equivalent acceleration voltage developed in the laser-generated plasma. A possible model suggests that this voltage is due to a momentary anisotropic charge distribution localized in front of the ablated target and due to the faster electron emission followed by the slower ion emission from the expanding plasma. Assuming that plasma is in local thermal equilibrium (LTE) conditions and that the equivalent voltage is applied over a distance of the order of the Debye length, it is possible to evaluate the high electric field generated in the plasma. The application of a high magnetic field to the plasma region alters the linear trajectories of the charged particles ejected from plasma in vacuum and modifies the resulting electric field. Ducruet et al. [2] and Wolowski et al. [3] demonstrated that the magnetic field confinement of the laser-generated plasma increases the recombination effects, decreases the mean energy of the ions and increases the current density of the ions along the normal direction. 34th EPS Conference on Plasma Phys. Warsaw, 2 - 6 July 2007 ECA Vol.31F, P-5.012 (2007)