San Diego, California, 17-19 June 2002

Investigation of Secondary Processes by Interaction of Plasma Streams with Various Materials

Khaydarov R.T., Bedilov M.R., Berdiyorov G.R., Kunishev U.S.,

Kholmuratov M.G., Tajikhanov E.

Scientific-Research Institute of Applied Physics at the National

University of Uzbekistan, Tashkent, Uzbekistan

ragabiaph.tkt.uz

ragabtkt.uz

Damages of the first wall by expanding products of micro-explosion (fast ions, debris) is one of the most significant problems for the design of the reactor chamber, experimental modeling of interaction processes and for choice of materials of the first wall in different IFE scenarios.

This work is denoted to study charge, energy spectra and current features of ions, generated at the interaction of laser-produced plasma (W, V, Mo, Nb) with the surface Al and Mo. Experiments were carried out by using as diagnostic tool the laser mass-spectrometer with mass resolution of m/D m =100 and with time-of- flight distance 100 cm. Neodymium glass laser providing power density q=5× 10¹⁰ W/cm² was used. Characteristics of plasma ions were measured in two cases: at presence of secondary target and without one. The secondary targets, intended for removing the ions to the laser mass-spectrometer, are in the form of plates made of Al and Mo, with (0,4 x 20) mm size slot in the center. They were installed parallel to the surface of primary targets. The distance between primary and secondary targets were changed within (5 -15) mm.

Analyzes of experimentally obtained data have shown that the presence of secondary targets Al, Mo on the way of laser-produced plasma expansion changes the charge and energy spectra of multiply charged ions. It was found that at the presence of secondary targets the energy spectra of highly charged ions are wider than in the case of free expansion. Registered maximum charge of ions in both cases is Z_max=6. The form of energy spectra of multiply charged ions at the presence of secondary dartboards is more informative, than in the case of free expansion. This fact shows that in the first case the temperature of electrons in plasma is greater than in the case of free expansion. The changes of the charge and energy spectra of multiply charged ions of plasma at the interaction W, Mo, Nb, V plasmas with the surface secondary dartboards Al, Mo can be explained by arising of a shock wave at collisions of supersonic plasma flows with the secondary targets.

In this work it was also given experimentally obtained data of spectra of multiply charged ions, emitted from the surface of Al target under the action of laser radiation of different frequencies. Herewith it was found experimentally that the increasing of laser frequency (q=const) leads to the nonlinear changing of intensity of single charged ions Al¹⁺, and intensity and emission of multiply charged ions increases due to the significant changing the focusing condition of laser radiation and ionization processes on surfaces Al.

Physical processes leading to changing of plasma ions features at the interaction of laser-produced plasma by the secondary targets are under discussion.