Fusion research progress

Source: Burning plasma achieved in inertial fusion | Nature

Abstract

Obtaining a burning plasma is a critical step towards self-sustaining fusion energy1. A burning plasma is one in which the fusion reactions themselves are the primary source of heating in the plasma, which is necessary to sustain and propagate the burn, enabling high energy gain. After decades of fusion research, here we achieve a burning-plasma state in the laboratory. These experiments were conducted at the US National Ignition Facility, a laser facility delivering up to 1.9 megajoules of energy in pulses with peak powers up to 500 terawatts. We use the lasers to generate X-rays in a radiation cavity to indirectly drive a fuel-containing capsule via the X-ray ablation pressure, which results in the implosion process compressing and heating the fuel via mechanical work. The burning-plasma state was created using a strategy to increase the spatial scale of the capsule2,3 through two different implosion concepts4,5,6,7. These experiments show fusion self-heating in excess of the mechanical work injected into the implosions, satisfying several burning-plasma metrics3,8. Additionally, we describe a subset of experiments that appear to have crossed the static self-heating boundary, where fusion heating surpasses the energy losses from radiation and conduction. These results provide an opportunity to study α-particle-dominated plasmas and burning-plasma physics in the laboratory.
. . .​

This report is about a decades long attempt to make fusion by laser implosion. This is not even close to a practical power plant but another incremental step for our understanding. It is a lab experiment with more insights to how fusion works. But there is a parallel, a micro hydrogen bomb.

My understanding, a hydrogen bomb is a fission ignited fusion reaction with some clever twists. The fission device effectively ignites a fissionable cylinder filled with the hydrogen filler, a lithium-hydrogen compound. The initial neutrons convert the lithium to a fusion-friendly hydrogen already adjacent in a compound with the other hydrogen. The cylinder compresses the filler to ignite the fusion reaction and the fusion reaction creates more neutrons to fission the cylinder and the subsequent heat results in compression and further fusion and heating. But it only works once like this fusion pellet experiment in miniature.

Elon says 'A prototype is easy but production is much, much harder.' But you need the lab and prototype to begin understanding how to make a production system. Regardless, even if you don't understand the maths, this is a good read.

Bob Wilson