Abstract Details
Conditions for the formation of “fast” ions at moderate intensity of laser radiation
Author: Rajabbay M Khaydarov
Requested Type: Poster Only
Submitted: 2009-03-19 02:26:52
Co-authors: Bedilov M., Beisinbaeva H., Khalbaev A.,
Contact Info:
Institute of Applied Physics
Vuzgorodok
Tashkent, Tashkent 100174
Uzbekistan
Abstract Text:
We have studied formation of charge, energy, dynamical and quantitative characteristics of multicharged ions (MCI) in laser-produced plasma as a function of power density of laser radiation (q) in the range of q=10^10-10^12 W/cm^2 and in the range of interaction angle θ=10˚-85˚. Experiments are carried out in a time-of-flight mass-analyzer connected to electrostatic analyzer. The mass resolution of the analyzer is ~100, time-of-flight distance of ions 350 cm. The vacuum in the system was kept as 10^-6 Tor. To exclude the effect of residual gases, adsorbed by the target, the target surface was first cleaned by the laser. We have used targets made of Al, Ni, Cu, Co. Additionally we have studied the ability of the laser to absorb probing electromagnet radiations, with the same parameters for the formation of plasma streams.
Mutual analysis of the characteristics of ions in laser plasma with the results obtained during the study of its properties to absorb heating electromagnet radiation shows that for these experimental conditions the optimal condition for absorption, formation and emission of MCI are obtained for θ= 18˚±5˚. We found that for all the samples the maximal charge of ions Zmax increase abruptly for smaller angle θ (θ= 18˚±5) and “larger” q (q≥7*10^11 W/cm^2).
We have shown that charge and energy state of plasma, as well as the emission of ions, formed at smaller q, can be increases not only by increasing the laser intensity, but also by polarization of the laser radiation. For example, if the maximal charge of Co ions equals to +6 in the absence of polarization, while it is equal to +11 in the case of P-polarized radiation, and ions with charge Co+9 in the case of S-polarized radiation.
We have also found that in the energy spectra of ions formed at P-polarized laser radiation with q≥7*10^11 W/cm^2, addition maximum is found in high energy range which is absent in the case of S-polarized radiation. The estimation of the velocity of ions drift with energy at the addition al maximum reaches the value 10^8 cm/s, which is much larger than the velocity of ions at the main maximum of the spectra.
The experimental results also showed that the formation of “fast” ions does not take place at angles larger than θ= 18˚±5. We think that generation of fast ions at small angles and P-polarized laser radiation can be explained by the absorbing properties of the plasma the laser radiation and by processes of resonant acceleration.
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