Laser-single cluster interaction

: modelling and understanding laser-single cluster interaction for cluster fusion

Abstract

When an ultrashort, intense laser pulse interacts with a nano-cluster (radius ~ nm, solid-state density), high ion energies and high ion charges are obtained in a very short amount of time. These high ion energies can be used to induce fusion reactions: cluster fusion. In current cluster fusion experiments sub nanosecond neutron pulses of 104 - 106 neutrons per pulse with Q-values of 10-8 - 10-7 are obtained. We have devised a simplified process-based laser-single cluster interaction model for ascertaining the theoretical feasibility of single cluster fusion (fusion within one exploding nano-cluster upon laser irradiation) and for ascertaining the possibility of generating mono-energetic ion energy spectra from a single cluster for enhancing fusion yields in current cluster fusion schemes.Laser-cluster interaction has been dissected in three processes: inner field ionisation, electron ejection and cluster expansion. In low-Z laser-cluster interaction these processes occur sequentially. Field ionisation rapidly ionises the cluster, creating a nano-plasma. The resulting electron cloud is subjective to a driving force by the laser field and a retaining force by the ion cloud, resulting in a forced oscillator model for the electron cloud motion during the laser pulse irradiation, which is used for determining the portion of ejected electrons from the cluster. After electron ejection, the cluster obtains an ion charge excess causing the cluster to expand under its self-generated potential, accelerating the cluster ions to high energies when all electrons are ejected. In the case of high-Z laser-cluster interaction we have shown that the electron cloud oscillation and field ionisation processes occur simultaneously and have a synergistic effect on each other, which explains why extraordinarily high charge states can be obtained by laser-single cluster interaction.We used our process-based model to show that it is theoretically possible to obtain nuclear fusion for deuterium-deuterium, deuterium-tritium and proton-boron fuel mixes from a single exploding nano-cluster by using peaked density cluster profiles and/or by combining ion species with a different mass/charge ratio. Single cluster fusion results in a sub picosecond neutron (deuterium-deuterium, deuterium-tritium fusion) /? radiation (proton-boron fusion) pulse, which can potentially lead to very high instantaneous (pulsed) neutron/? fluxes of up to 1022 - 1024 n, ? / m2 s. Additionally, we have shown it is theoretically possible to obtain mono-energetic ion energy spectra from cluster fusion by controlling the density profile in a double pulse set-up, which can enhance the fusion yield in current cluster fusion schemes by up to a factor 4.

Date of Award	31 Aug 2014
Original language	English
Supervisor	G.J.H. Brussaard (Supervisor 1) & Niek Lopes Cardozo (Supervisor 2)