How will you generate high gain from the targets?

Summary

Despite only a handful of design shots available to the team over the past 2.5 years, evolution of the target design has already achieved two doublings of gain over the ignition shot in 2022. By scaling up the target for our 10MJ driver, the existing proven design increases gain to 18x (Qeng>1). And with unlimited design shots available on our 10 Hz laser, we can rapidly progress toward another doubling of gain which is needed for our 1.5GW power plant.

Prior designs of a fusion power plant called for gains of 100x or more in order to generate electricity. Currently, the National Ignition Facility (NIF) target’s best design has netted a gain of 4x. So, an open question is how we would plan to scale the yield from 4x today at NIF to 100x.

The short answer is we don’t have to scale to 100x. We only need 20x for our first “pilot plant”, and then 35 to 45x for commercial power production. And increasing the laser energy from ~2 MJ to 10 MJ means we can use much larger and simpler targets.

At ~2 MJ, the NIF laser is flirting with the absolute minimum amount of energy to make ignition possible. They’re running into physics limitations on how much fuel compression and confinement is possible at such low energies, limiting the maximum achievable energy.

But our fusion power plant is designed around a much larger, much more efficient 10 MJ diode-pumped, solid-state laser (See “Why a DPSSL?”). Scaling up the proven 2 MJ NIF target to 10 MJ increases the amount of fuel in the target, and increases the confinement and burn, relaxing the adiabatic constraints. Basically, a bigger target unleashes a non-linear amount of energy.

Our first goal is to show that we can close the fuel cycle (see “How much fusion energy do you need?”) and make enough fusion to send power to the grid. This requires a gain of just 18x. This is achievable from a direct scale up of the proven NIF target from 2 MJ to 10 MJ, with low risk. For a 1.5GW power plant, our design calls for a gain of 45, or approximately 2.5x more than the 18x yield from a direct scale-up.

Target design evolution has unlocked greater and greater gains for the past several years at NIF. Once we have a 10 MJ laser that can be shot 10 times per second, we will rapidly evolve target designs with ideas that can’t reasonably be tested today.

With only a handful of development shots per year, the team at NIF has expanded the yield 6x since 2021. If we can test target designs as frequently as we want, we will remove the primary limiter on progress toward higher yield targets. From 18x gain, which is already designed into our baseline target, to 50x, which is our nominal goal, is merely an improvement of 2.5 times. With unlimited design shots available on our laser, we believe that goal is readily achievable.