Observations and properties of the first laboratory fusion experiment to exceed a target gain of unity

An indirect-drive inertial fusion experiment on the National Ignition Facility was driven using 2.05 MJ of laser light at a wavelength of 351 nm and produced $3.1\pm 0.16$ MJ of total fusion yield, producing a target gain $G=1.5\pm 0.1$ exceeding unity for the first time in a laboratory experiment [Phys. Rev. E 109, 025204 (2024)]. Herein we describe the experimental evidence for the increased drive on the capsule using additional laser energy and control over known degradation mechanisms, which are critical to achieving high performance. Improved fuel compression relative to previous megajoule-yield experiments is observed. Novel signatures of the ignition and burn propagation to high yield can now be studied in the laboratory for the first time.

Figure 1

(a) Laser pulses as delivered for N220919 and N221204 versus N210808. (b) Measured radiation temperature $T_{\text{rad}}$ from Dante 1 versus time. Since the Dante 1 data are not available for N210808, data from several shots that repeated the same laser pulse are shown in blue. Dante data are shown until 100 ps before peak nuclear production.

Figure 2

Angularly resolved nuclear activation maps from a series of experiments showing a progression of reduced mode 1 symmetry impact. Shown below each plot are the hot spot velocity and inferred mode-1 $\rho R$ perturbation (modes $>$ 1 are suppressed by RTNAD sampling effects [39]). In each panel $\times$ marks the direction of the hot spot velocity, with the red ellipse denoting the uncertainty and the circles the real-time nuclear activation diagnostic locations.

Figure 3

Equatorial view of the time-integrated neutron emission showing the impact of low-mode asymmetries on the fusion yield for pairs of experiments conducted with (a) and (b) 1.9 MJ of laser energy and (c) and (d) 2.05 MJ of laser energy. The $17\%$ contour of emission is denoted by the red solid line. The inset in (a) shows the hohlraum orientation with respect to the image, and for each experiment the mode 2 amplitude $P_2$ is given. The mode 1 amplitude for each experiment is given in Fig. 2.

Figure 4

The $4\pi$ averaged downscattered ratio vs the average radius of neutron emission for the 1.9-MJ design (circles) and 2.05-MJ design (squares). The color of the datum corresponds to the fusion yield of the experiment.

Figure 5

(a) Neutron spectra and apparent DT ion temperature, from 1.9-MJ laser energy experiments N220109 (black) and N210808 (red) and from a 2.05-MJ laser energy experiment N221204 (blue). (b) Neutron-emission duration as fusion yield. (c) Inferred hot spot mass for 1.9- and 2.05-MJ laser experiments. In (b) and (c) experiments N220109 (black), N210808 (red), and N221204 (red) are highlighted.

Figure 6

X-ray- and neutron-emission measurements from (a), (c), and (e) N210808 and (b), (d), and (f) N221204, with time-integrated x-ray emission (greater than 10 keV) from (a) N210808 and (b) N221204 and time-integrated neutron emission from (c) N210808 and (d) N221204. Also shown is a comparison of contours that enclosed $50\%$ of the x-ray and neutron emission for (e) N210808 and (f) N221204. Further details of the x-ray imaging diagnostic are given in the Appendix.

Figure 7

Hot spot ion temperature and areal density. Thresholds for the burning-plasma criterion (solid line) and static self-heating (dashed line) are shown with NIF data. Here the ion temperature is inferred from the width of the DD neutron spectra.

Figure 8

Inferred yield amplification and ${\text{ITFX}}_{\alpha }$ for NIF experiments culminating in N221204.

Figure 9

Inferred hot spot pressure and energy, inferred (a) without the presence of self-heating and (b) directly for the burn-on experiments. Contours of $E{P}^2$ relative to N210808 in both cases are shown.