J. Plasma Fusion Res. SERIES, Yol.2 (1999) 4lMl3 Velocity Distribution of lons and Anisotropy of Kinetic lon-Temperatures in Laser Plasma Experiments

Using a 200 mJ, 5ns Nd: YAG laser the velocity distribution of ions in the plane of incidence, at angles ranging from-17.5 ' to 60 " with reference to the normal to the target plane was investigated at a laser intensity of approximately 7 x 10r\M/cm2. The time of flight spectra of the ions of each ionization state for the elements carbon, aluminum, nickel and tantalum were obtained. The kinetic temperatures of ions of each ionization state and each element were estimated, on the plane of incidence, and the results are presented. From the experimental results and their analysis it was observed that the velocity distribution function of the ions departed significantly from a Maxwellian one and the ion-temperatures of the expanding plasma were found to be highly anisotropic. Keywords: Ion-temperature, distribution function, laser-plasma interaction distribution and their observation has also drawn conviction from reported works of the earlier investigators [3-5]. In the present work our motivation is to determine whether the velocity distribution of ions under consideration (carbon, aluminum, nickel and tantalum) is truly Maxwellian or has a departure from it as well as the ion-temperatures are fully thermalized and isotropic. We have determined the time of flight spectra of the ions of each ionization state and their kinetic temperatures for different angles in the plane of incidence. From the experimental results and their analysis it is observed that the particle distribution function departs significantly from a Maxwellian and the ion-temperatures of the expanding plasma were found to be anisotropic leading to a conclusion that the energy equipartition between electrons and ions has not taken place. The other supplementary conclusions are presented and the results are discussed