Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

High energy electron transport in solids

With the addition of recent PW shots, the propagation of short-pulse laser generated electron beams have been studied using laser pulse energies from 30 J to 300 J, generating currents up to ∼15 MA in solid Al:Cu targets. This is ∼5% of the current that will be required in an ignition pulse. To this level, the current appears to simply scale with laser power, the propagation spread not change at all. The resistance of the aluminum does not seem to play a role in the propagation characteristics, though it might in setting the current starting parameters. We do find that at the highest currents parts of these targets reach temperatures high enough to modify the Cu-K2 emission spectrum rendering our Bragg imaging mirrors ineffective; spectrometers will be needed to collect data at these higher temperatures. © EDP Sciences