High-Sensitivity Thomson Spectrometry in Experiments of Laser-Driven Low-Rate NeutronLess Fusion Reactions

Abstract

The aneutronic 11B(p, α)2α fusion reaction driven by the interaction of high-energy lasers with matter has become a popular topic of research, since it represents a potential long-term goal alternative to the most studied deuterium-tritium reaction. However, the detection of the typical ionic products, especially alpha particles, of this low-rate fusion reaction is a challenging issue, due to their low flux. One of the diagnostic devices that can be implemented in laser-driven proton-boron fusion experiments is a Thomson spectrometer (TS), which is capable of detecting and discriminating ions according to their mass-to-charge ratio ( A / Z , where A is the mass number and Z is the atomic number of the ions). In this work, we report on the ultimate test of a TS, which was designed and developed at the ENEA Research Centre in Frascati, Italy, in the context of a p + 11B fusion experiment. Our device—designed to have high sensitivity and a robust shielding against electromagnetic pulses (EMPs)—was implemented at the PALS laser facility (∼700 J in ∼350 ps pulses) at a distance of 367 mm from the laser-plasma interaction point. We analyse here the measured signals obtained with our device, focusing on the assessment of their signal-to-background ratio. Despite the presence of strong EMPs and background radiation at such a short distance from the laser-irradiated target, the TS proved to be suitable for effectively detecting protons and heavier ions stemming from the plasma source.

Perspectives on research on laser driven proton-boron fusion and applications

“…The first attempt of going beyond this stage by applying advanced machine learning capabilities so to automatically classify particle tracks in CR39 and differentiate between different particles and different energies has been made by Amit, Nissim et al [57]. Detection of α-particles is difficult in Thomson parabola spectrometers [52,58,59] because their trace is superimposed to those of ions with the same charge/mass ratio (0.5), such as fully stripped C, O, B, etc. For example, α-particles will have the same position as 12 C 6+ ions with three times bigger energy.…”

“…Due to the limitation of state-of-the-art diagnostic approaches, it is necessary to develop innovative new diagnostic methods [19,[58][59][60][61], or modify and upgrade the existing solutions. For instance, it will be possible to get information on pB reactions from studying other reactions occurring in the same experiment, and secondary generating products that can be detected more easily.…”

Future for inertial-fusion energy in Europe: a roadmap

“…EU laboratories and universities have recognized historical experience in the development of advanced diagnostics for the described ICF/IFE scenarios, and in general for lasermatter experiments [83,150,152,[157][158][159][160][161][162][163][164][165][166][167][168][169] . They are thus capable of supplying a solid base for the innovation steps required for future IFE projects; in particular, for devices and methodologies that have to run on HRR regimes with associated data handling issues and with the requirement of high sensitivity in an environment heavily polluted by radiation and EMPs.…”

“…A strong contribution to diagnostic development is expected for the fundamental IFE requirement of running experiments in high-intensity and HRR laser facilities [83,[157][158][159][160][161][162][163][164] . Another significant issue is to develop highsensitivity diagnostics [162,[165][166][167][168][169] , in an environment heavily polluted with high radiation doses and with laser-generated EMPs of high intensity, as discussed in the next section.…”