THE GENERATION OF FAST PARTICLES IN PLASMAS CREATED BY LASER PULSES WITH DIFFERENT WAVELENGTHS
Rosmej F.B., Stepanov A.E., Hoffmann D.H.H., Faenov A.Ya., Sub W., Geibel M., Pirzadeh P., Seelig W., Skobelev I.Yu., Magunov A.I., Pikuz T.A., Bock R., Letardi T., Flora F., Bollanti S., Lizzaro P.Di., Satov Yu.A., Smakovskii Yu.B., Roerich V.K., Khomenko S.V., Makarov K.N., Starostin A.N., Reale A., Scafati A., Auguste T., d'Oliveira P., Hulin S., Monot P., Sharkov B.Yu.

Received: July 30, 2001

PACS: 52.25.-b, 52.70.-m

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By means of spatially resolved high-resolution X-ray spectroscopy, we have investigated the generation of fast ions at various laser installations with different flux densities and laser wavelengths. It is demonstrated that the fast ion generation in laser-produced plasma can be achieved for a very low level of the averaged laser intensity onto the target. The time-of-flight mass spectrometry ion diagnostics and X-ray spectrographs give very close results for the energy distribution of the thermal ion component. For higher energies, however, we found significant differences: the spatially resolved high-resolution spectrographs expose the presence of supra-thermal ions, while the time-of-flight method does not. Supra-thermal ion energies E_ion plotted as a function of the qλ² parameter show a large scatter far above the experimental errors. The cause of these large scatters is attributed to a strong non-uniformity of the laser intensity distribution in the focal spot. The analyses by means of hydrodynamic and spectral simulations show that the X-ray emission spectrum is a complex convolution from different parts of plasma with strongly different electron density and temperature. It is shown that the highly resolved Li-like satellite spectrum near He_α contains significant distortions even for very low hot electron fractions. Non-Maxwellian spectroscopy allows determinating both the hot electron fraction and the bulk electron temperature.