Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain $G_{\text{target}}$ of 1.5. This is the first laboratory demonstration of exceeding “scientific breakeven” (or $G_{\text{target}}>1$) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Figure 1

Left: schematic of the target and laser configuration including the hohlraum. Bottom right: the HDC capsule and DT fuel configuration. Top right: total laser power vs time and radiation temperature $T_r$ as a function of time. The HDC capsule thickness was increased by $\sim 7\%$ and the laser energy was increased by $\sim 7.9\%$ for N221204 (red line) compared to N210808 (black line).

Figure 2

Target gain vs calendar date. The horizontal labels mark the beginning of each year. The color of the narrow target gain bars represents different implosion designs, and the dashed horizontal line represents the target $\text{gain}=1\mathrm{per}$ the NAS ignition criteria [26].

Figure 3

3D reconstruction of the time-integrated emission-weighted neutron emissivity from two neutron images taken on each shot from orthogonal lines of sight (image projections), for NIF shots (a) N210307, (b) N210808, and (c) N221204. The left color bar corresponds to the 3D represented volume; the right color bar is for the 2D projections of this volume.

Figure 4

NIF DT shot data are plotted in the space of inferred hot spot Lawson parameter which corresponds to hot spot peak pressure times burn duration, $p\tau$, and DD ion temperature, which is the temperature $T$ determined by the neutron-time-of-flight spread of 2.5 MeV neutrons that come from deuterium-deuterium fusion. The curves denote the ignition boundary per the GLC equation described in the text assuming no mix (solid) and with a multiplier of 1.5 and $2\times$ on the radiative loss to account for increased levels of higher atomic number mix (dashed curves). Experiments N210808 and N221204 exhibit little mixing, $\overline{Z^2}\sim 1.03\pm 0.02$, while other experiments can exhibit higher values depending upon capsule quality, fill-tube size, and hydrodynamic instability control. Data from the Hybrid-E series are highlighted as red points, while earlier campaigns are shown in other colors.