On thermonuclear processes in cavitation bubbles

The theoretical and experimental foundations of so-called bubble nuclear fusion are reviewed. In the nuclear fusion process, a spherical cavitation cluster $\sim 10^{-2}$ m in diameter is produced of spherical bubbles at the center of a cylindrical chamber filled with deuterated acetone using a focused acoustic field having a resonant frequency of about 20 kHz. The acoustically-forced bubbles effectuate volume oscillations with sharp collapses during the compression stage. At the final stages of collapse, the bubble cluster emits 2.5 MeV D–D fusion neutron pulses at a rate of $\sim 2000$ per second. The neutron yield is $\sim 10^5$ s$^{-1}$. In parallel, tritium nuclei are produced at the same yield. It is shown numerically that, for bubbles having sufficient molecular mass, spherical shock waves develop in the center of the cluster and that these spherical shock waves (microshocks) produce converging shocks within the interior bubbles, which focus energy on the centers of the bubbles. When these shock waves reflect from the centers of the bubbles, extreme conditions of temperature ($\sim 10^8$ K) and density ($\sim 10^4$ kg m$^{-3}$) arise in a (nano)spherical region ($\sim 10^{-7}$ m in size) that last for $\sim 10^{-12}$ s, during which time about ten D–D fusion neutrons and tritium nuclei are produced in the region. A paradoxical result in our experiments is that it is bubble cluster (not streamer) cavitation and the sufficiently high molecular mass of (and hence the low sound speed in) D-acetone ($\rm C_{3}D_{6}O$) vapor (as compared, for example, to deuterated water $\rm D_{2}O$) which are necessary conditions for the formation of convergent spherical microshock waves in central cluster bubbles. It is these waves that allow the energy to be sufficiently focused in the nanospherical regions near the bubble centers for fusion events to occur. The criticism to which the concept of ‘bubble fusion’ has been subjected in the literature, in particular, most recently in Uspekhi Fizicheskikh Nauk (Physics – Uspekhi) journal, is discussed.