One of the most promising approaches to reach a high gain in inertial confinement fusion is the fast ignition scheme. In this scheme, a relativistic electron beam is generated; this passes through the imploded plasma and deposits parts of its energy in the core. However, the large angular spread of the relativistic electron beam and the poorly controlled compression of the target affect realization of the fast ignition technique. Here, we demonstrate that indirectly driven (that is, driven by X-rays generated inside a gold hohlraum) implosions with a ‘high-foot’ and a short-coast time of less than 200 ps allow us to tightly compress the shell. Furthermore, we show the ability to optimize the symmetry of the imploding shell by changing the hohlraum length, successfully tuning a suitable tube-shaped shell to compensate for the large angular spread of the relativistic electron beam and to enhance the electron-to-core coupling efficiency via resistive magnetic fields. Benefiting from those experimental techniques, a significant enhancement in neutron yield was achieved in our indirectly driven fast ignition experiments. These results pave the way towards high-coupling fast ignition experiments with indirectly driven targets similar to those at the National Ignition Facility.
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We thank all the SG-IIU technical staff at Shanghai Institute of Optics and Fine Mechanics for their support during the experiment. The research leading to these results has received funding from the Science Challenge Project, no. TZ2016005, the National Key Programme for S&T Research and Development (grant no. 2016YFA0401100), the National Natural Science Foundation of China (grants nos. 11975055, 11805182 and U1730449 (NSAF)). PIC and hybrid-PIC simulations were performed on the Tianhe-2 supercomputer (China).
The authors declare no competing interests.
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Zhang, F., Cai, H.B., Zhou, W.M. et al. Enhanced energy coupling for indirect-drive fast-ignition fusion targets. Nat. Phys. 16, 810–814 (2020). https://doi.org/10.1038/s41567-020-0878-9