Fuel gain exceeding unity in an inertially confined fusion implosion

Abstract

Ignition is needed to make fusion energy a viable alternative energy source, but has yet to be achieved. A key step on the way to ignition is to have the energy generated through fusion reactions in an inertially confined fusion plasma exceed the amount of energy deposited into the deuterium-tritium fusion fuel and hotspot during the implosion process, resulting in a fuel gain greater than unity. Here we report the achievement of fusion fuel gains exceeding unity on the US National Ignition Facility using a 'high-foot' implosion method, which is a manipulation of the laser pulse shape in a way that reduces instability in the implosion. These experiments show an order-of-magnitude improvement in yield performance over past deuterium-tritium implosion experiments. We also see a significant contribution to the yield from α-particle self-heating and evidence for the 'bootstrapping' required to accelerate the deuterium-tritium fusion burn to eventually 'run away' and ignite.

Improved Performance of High Areal Density Indirect Drive Implosions at the National Ignition Facility using a Four-Shock Adiabat Shaped Drive

“…Here, α is defined as α ¼ P=P cold , where P cold is the minimum pressure at 1000 g=cc from the DT EOS [17]. Increasing the α is one path to reduced ablation front hydrodynamic instability growth, and a hypothesis is that the reduced growth [18] led directly to improved performance demonstrated by the high-foot experiments [16]. The increased α is also predicted to lead to lower convergence, ρR, and yields in 1D simulations.…”

“…Experiments during the National Ignition Campaign (NIC) [9][10][11][12][13] were thought to have been degraded by both instability growth and in the most severe cases mix of plastic ablator material into the hot spot as a consequence of that growth. Subsequent experiments deliberately increased the adiabat (α) or entropy delivered to the DT shell, by increasing the laser foot (called high foot) to improve stability and performance [14][15][16]. Here, α is defined as α ¼ P=P cold , where P cold is the minimum pressure at 1000 g=cc from the DT EOS [17].…”

Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics

“…This was an early shot in the high-adiabat campaign [27]. 1.27 MJ of frequency-tripled 3ω (λ = 351 nm) laser energy (peak power 350 TW) drove a gold hohlraum filled with 1.45 mg/cm 3 of He, and a plastic capsule with D-He3 gas.…”

Time-resolved compression of a capsule with a cone to high density for fast-ignition laser fusion

“…For the current experiment, E L ¼ 18 kJ, l ¼ 0.35 mm and a inn ¼ 3.4, for which the simple expression yields B350 mg cm À 2 , only B17% higher than the actual value, showing that the scaling model can be used to estimate the expected (rR) max for different energies and adiabats. For a laser energy of 1.9 MJ, which was used in a recent experiment 6 at the National Ignition Facility, and for a inn ¼ 3.4, a value of (rR) max ¼ 1,600 mg cm À 2 is estimated, which is a factor of B4.6 higher than with OMEGA. A higher areal density allows for particle stopping up to a higher kinetic energy and, given a certain distribution of kinetic energies, relaxes the requirement to ignite the fuel.…”

“…Pressures of B10 16 Pa prevail in the sun's core, whereas they are B100 Â lower in the core of giant planets. An important step towards ignition has been recently demonstrated by measuring fusion energy that exceeds the energy coupled in the fuel in an inertial confinement fusion implosion 6 . So far, ignition has not been reached despite code predictions.…”