A laser application to nuclear astrophysics

Abstract

In the last decade, the availability in high-intensity laser beams capable of producing plasmas with ion energies large enough to induce nuclear reactions has opened new research paths in nuclear physics. We studied the reactions 3He(d, p)4He and d(d,n)3He at temperatures of few keV in a plasma, generated by the interaction of intense ultrafast laser pulses with molecular deuterium or deuterated-methane clusters mixed with 3He atoms. The yield of 14.7 MeV protons from the 3He(d, p)4He reaction was used to extract the astrophysical S factor. Results of the experiment performed at the Center for High Energy Density Science at The University of Texas at Austin will be presented

Model-independent determination of the astrophysicalSfactor in laser-induced fusion plasmas

“…However, this method generally requires an excellent measure of the energetic tail of the ion distribution, especially for reaction (3). Thus, we calculate the proton yields of reaction (3) using the deuterium ion energy distribution and the S-factor obtained in [22], then, by means of a minimization algorithm, we evaluate the proper energy cut to apply in order to best match the experimental data coming from the proton detectors Y (exp) p . Then we apply the same cut to calculate the neutron yields of reaction (1) and compare that to the experimental data from neutron detectors Y (exp) n to obtain the S-factor.…”

“…It gives the highest contribution to the fusion yields. Fitting the ion signal requires the introduction of a model for the ion energy distribution (usually assuming thermalization which is quite justified in the present experiment [22,28]). We would like to propose an alternative method based entirely on the measured quantities which allows us to extract the S-factor.…”

“…Thus the ion energy distribution is obtained by subtracting the yield value at such cutoff energy. Of course other methods are possible to estimate the background [21,22]. As we will show below, a small shift in such a cutoff will have a large effect on the analysis for reaction (3), but smaller for the reaction (1) since the latter is sensitive to the ion energy region around 30 keV (the effective Gamow peak energy region for this reaction), a region where the ion signal is usually not greatly affected by the laser-induced noise, as shown in Fig.…”

“…We also derive the S-factor for the reaction (3), but the measurements have large error bars in the region of interest. In such a case, a better description is obtained by fitting the experimental signal with a Maxwell-Boltzmann distribution [21,22,27,28]. However, we would like to present a general method which does not involve any particular assumption for the ion energy distribution function.…”

“…Thanks to the rapid development of high-intensity lasers, many facilities have the capability of delivering petawatt laser pulses onto small targets, providing new insights on light-matter interactions and nuclear physics. In particular, the Coulomb explosion [19][20][21][22][23][24] of D 2 molecular clusters induced by their interaction with an intense laser pulse gives the possibility of studying many nuclear reactions at very low energies inside a highly ionized medium.…”