Design of inertial fusion implosions reaching the burning plasma regime

Abstract

In a burning plasma state1–7, alpha particles from deuterium–tritium fusion reactions redeposit their energy and are the dominant source of heating. This state has recently been achieved at the US National Ignition Facility8 using indirect-drive inertial-confinement fusion. Our experiments use a laser-generated radiation-filled cavity (a hohlraum) to spherically implode capsules containing deuterium and tritium fuel in a central hot spot where the fusion reactions occur. We have developed more efficient hohlraums to implode larger fusion targets compared with previous experiments9,10. This delivered more energy to the hot spot, whereas other parameters were optimized to maintain the high pressures required for inertial-confinement fusion. We also report improvements in implosion symmetry control by moving energy between the laser beams11–16 and designing advanced hohlraum geometry17 that allows for these larger implosions to be driven at the present laser energy and power capability of the National Ignition Facility. These design changes resulted in fusion powers of 1.5 petawatts, greater than the input power of the laser, and 170 kJ of fusion energy18,19. Radiation hydrodynamics simulations20,21 show energy deposition by alpha particles as the dominant term in the hot-spot energy balance, indicative of a burning plasma state.

Self-heating plasmas offer hope for energy from fusion

“…Writing in Nature, Zylstra et al [1] answer one such question by showing that, in the laser-driven approach to fusion, in which a plasma is compressed and heated, the plasma can be further heated by the fusion reactions themselvesa key requirement for self-sustaining fusion energy. Companion papers from the same group of researchers, by Kritcher et al [2] in Nature Physics and Ross et al [3] on the arXiv preprint server, detail the process of optimizing the experiment design.…”

“…The heated walls radiate X-rays (not shown), which compress the plasma inwards, but this compression can be asymmetric, leading to energy losses. b, Through simulations [2] and experiments [3], the team optimized the set-up, introducing a photonic structure (not shown) at the hohlraum entrance to transfer laser power to the beams close to the interior, and altering the shape of the hohlraum. These improvements increased the symmetry of the compressed plasma, resulting in an energy increase.…”

Role of self-generated magnetic fields in the inertial fusion ignition threshold

“…In section four, we show how the self-magnetization model can be included into the hot-spot energy balance equations, allowing a dynamic self-magnetized hot-spot model. We show that self-magnetization effects should increase strongly with temperature, becoming a key consideration in the record burning plasmas of recent NIF experiments [29][30][31] . Section five provides a conclusion and discussion of assumptions.…”

Initiator enhancement of mandrel degradation for ICF target fabrication

“…The polymer degradation is not only an important topic in the environment protection ( Wang et al., 2016 ; Yang et al., 2009 ; Guo et al., 2012 ; Rhodes, 2018 ; Xu et al., 2019 ) but also the key process for the fabrication of nuclear fuel targets used in inertial confinement fusion (ICF) ( Zhang et al., 2020 ; Glenzer et al., 2010 ; Betti and Hurricane, 2016 ; Hurricane et al., 2014 ). In particular, the latest progress in achieving burning plasma and reaching the ignition threshold signals a big step toward delivering the promise of nuclear fusion as the ultimate solution to energy problems ( Kritcher et al., 2022 ; Zylstra et al., 2022 ; Clery, 2021 ). As the quality of ICF targets can directly influence the ignition experiments, there is an urgent need to develop new strategies to improve the targets.…”