Acceleration of the d+d reaction in metal lithium acoustic cavitation with deuteron bombardment from 30 to 70 keV

Fusion reactions ${}^{6}\mathrm{Li}(d,\ensuremath{\alpha}){}^{4}\mathrm{He}$ and ${}^{2}\mathrm{H}{(d,p)}^{3}\mathrm{H}$ were measured in liquid Li. An ultrasonic target system was developed to form acoustic cavitation bubbles in liquid Li as an additional target. The material uncertainties of the target surface, which have been noted in solid target experiments, were completely rejected because contaminants could be removed in the liquid phase. The $\mathrm{Li}+d$ reaction was not affected by the cavitation process, and the derived screening potential was ${U}_{s}=543\ifmmode\pm\else\textpm\fi{}38$(sta.) ${}_{\ensuremath{-}153}^{+83}$(sys.) eV. This value can be explained by ionic Debye screening if liquid Li is regarded as a low-temperature dense plasma. The $d+d$ reaction was found to be enhanced several times by Li cavitation, whereas the yield of the $\mathrm{Li}+d$ reaction remained constant; the ultrasonic effect depends strongly on the target conditions. The enhancement is caused not by Coulomb screening but by the high deuteron temperature in the cavity. The temperature was deduced from the energy dependence of the nuclear reaction enhancement rate as $k{T}_{d}=590\ifmmode\pm\else\textpm\fi{}54$(sta.) ${}_{\ensuremath{-}457}^{+676}$(sys.) eV. A kinematic analysis also yielded consistent results. Although no meaningful bubble fusion events were observed, extremely large reaction enhancements were occasionally observed.