Pushered single shell design lowers ignition threshold for fusion reactions
Pushered single shell design lowers ignition threshold for fusion reactions lead image
In an inertial confinement fusion reaction, a nuclear fuel capsule is compressed until it reaches an ignition threshold where it undergoes fusion. Commonly, these capsules are made of a low-Z material, like plastic, and rely on high particle velocities to create the compression energy.
An alternative method, called a pushered single shell, instead relies on a high-Z material, a blend of chromium and beryllium, which can be stabilized with a density gradient and requires less energy and lower velocities.
Dewald et al. report the first experimental tests with a new graded pushered single shell design. These suggest the implosion is stable and has a similar performance to low-Z capsule implosions.
“We measured the timing of the shock propagating through the capsule inside of the fuel, and we radiographed the capsules to make sure they’re fairly round when they implode and we can control the shape of the compression,” said author Eduard Dewald. “So far, the experiments confirmed the possibility of using these capsules to obtain predicted fusion yields.”
The biggest downside to using a pusher is that the high-Z material can mix with the fuel. However, these experiments curb that effect with a low-Z anti-mix layer. Additionally, the design is graded so the high-Z material transitions gradually to a low-Z material at the ablation front, mitigating instability growth.
The team is planning to improve the efficiency of the design.
“We are going to use different shape drives to allow us to adjust the mix between the shell and the fuel to see how the implosion responds,” said Dewald. “And we are going to use an ice layer of fuel, which promises a high yield in simulations.”
Source: “First graded metal pushered single shell capsule implosions on the National Ignition Facility,” by E. L. Dewald, S. A. MacLaren, D. A. Martinez, J. E. Pino, R. E. Tipton, D. D.-M. Ho, C. V. Young, C. Horwood, S. F. Khan, E. P. Hartouni, M. S. Rubery, M. Millot, A. R. Vazsonyi, S. Vonhof, G. Mellos, S. Johnson, V. A. Smalyuk, F. Graziani, E. R. Monzon, R. Tommasini, D. Alessi, S. Ayers, G. N. Hall, J. Holder, D. Kalantar, A. J. MacKinnon, J. Okui, M. Prantil, J.-M. Di Nicola, T. Lanier, A. Thomas, S. Yang, H. W. Xu, H. Huang, J. Bae, C. W. Kong, N. Rice, Y. M. Wang, P. Volegov, M. S. Freeman, and C. Wilde, Physics of Plasmas (2022). The article can be accessed at https://doi.org/10.1063/5.0083089 .
