Author: Anita Pokorska

The team of researchers from the Institute of Plasma Physics and Laser Microfusion in Warsaw has performed systematic numerical (particle-in-cell) studies of the properties of laser-driven carbon ion beams produced under conditions relevant for ion fast ignition (IFI) of DT fuel, and the feasibility of achieving beam parameters required for IFI were discussed. The ignition of nuclear fuel initiated by an intense laser-driven ion beam is a promising option of Inertial Confinement fusion (ICF) which is currently one of the two main paths towards an energy source based on thermonuclear fusion. 

It was found that a 1 ps 200 kJ infrared laser driver is capable of producing ion beams with parameters required for IFI, even with a simple non-optimised target, but only at small distances (<0.1 mm) from the target. At such distances, the beam intensity and fluence exceeds 5 × 10²¹ W cm⁻² and 2 GJ cm⁻², respectively, while the beam energy approaches 30 kJ. The ion beam parameters can be significantly improved by carefully selecting the target thickness and shape. However, even with an optimised target, achieving the beam parameters required for IFI is possible only at distances from the target below 0.5 mm.  

It was shown for the first time that laser-accelerated heavy ion beams produced under conditions relevant for IFI achieve higher parameters determining fuel ignition than light ion or proton beams and, therefore, may be more useful for IFI than previously thought. 

The ion acceleration is accompanied by the emission of powerful (>50 PW) pulses of short-wavelength synchrotron radiation which are the source of significant ion energy losses and may pose a threat to the fusion infrastructure.  

In addition to ICF, the extremely intense ion beams can be a unique research tool for research in nuclear physics, high energy-density physics or materials science.

The intensity and the temporal shape of the ion pulse are two of the most important characteristics of the ion beam that determine the fuel ignition. These characteristics recorded at a distance x equal to 100 µm, 200 µm and 500 µm from the front of the target and averaged over the area of aperture d_ap = 50 µm (the “useful part of the beam”) for Li, C, Al, Ti and Cu ions are presented in figure. The highest peak intensity and the shortest duration are achieved by the Cu ion pulse, both in the near-expansion and far-expansion zone.