this post was submitted on 19 Feb 2025
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No magnetic confinement fusion reactor in existence has ever generated a positive output. The current record belongs to JET, with a Q factor of 0.67. This record was set in 1997.
The biggest reason we haven't had a record break for a long time is money. The most favourable reaction for fusion is generally a D-T (Deuterium-Tritium) reaction. However, Tritium is incredibly expensive. So, most reactors run the much cheaper D-D reaction, which generates lower output. This is okay because current research reactors are mostly doing research on specific components of an eventual commercial reactor, and are not aiming for highest possible power output.
The main purpose of WEST is to do research on diverter components for ITER. ITER itself is expected to reach Q ≥ 10, but won't have any energy harvesting components. The goal is to add that to its successor, DEMO.
Inertial confinement fusion (using lasers) has produced higher records, but they generally exclude the energy used to produce the laser from the calculation. NIF has generated 3.15MJ of fusion output by delivering 2.05MJ of energy to it with a laser, nominally a Q = 1.54. however, creating the laser that delivered the power took about 300MJ.
https://www.theguardian.com/environment/2023/aug/06/us-scientists-achieve-net-energy-gain-second-time-fusion-reaction
I've seen a few mentions of positive output in the last few years.
OK, so we should be clear there are broadly two approaches to fusion: magnetic confinement and inertial drive.
In magnetic confinement a plasma is confined such that it can be driven to sufficient density, temperature and particle confinement time that the thermal collisions allow the fuel to fuse. This is what the OP article is talking about. This Tokamak is demonstrating technologies that if applied to a larger the experiment could probably reach a positive energy output magnetically confined plasma.
The article you referenced discusses inertial drive experiments, where a driver is directly pushing the fuel together, like gravity in the sun, a fission bomb shockwave in a hydrogen bomb, or converging laser beams in Livermore's case.
Livermore's result is exciting, but has no bearing on the various magnetic confinement approaches to fusion energy.
Aha, thank you for clarifying. Not my area of expertise, did not know the difference.
The input energy doesnt matter that much. Nobody is going to use 1980s laser tech to power a real reactor. As with OP, inertial confinement is interested in very small nuanced science aspects, not making a power plant.
I wasn't aware of that distinction about the energy for the laser to generate the heat energy within the reaction not being factored into the Q value, very interesting, thank you! Would that energy for the laser still be required in a "stable reaction" continuously, or would it be something that would "trail off"?
Inertial confinement doesnt produce a "stable reaction" it is pulsed by it's nature, think of it in the same way as a single cylinder internal combustion engine, periodic explosions which are harnessed to do useful work. So no the laser energy is required every single time to detonate the fuel pellet.
NIF isnt really interested in fusion for power production, it's a weapons research facility that occasionally puts out puff pieces to make it seem like it has civilian applications.
Your take is incorrect.
It would be more productive if you said how you think im wrong. Just saying 'youre wrong' doesnt really add anything to the discussion.
In my experience the community will usually distinguished between "scientific Q" and "wall plug Q" when discussing fusion power gain. Scientific is simply the ratio of power in vs power out, whereas wall plug includes all the power required to support scientific Q. Obviously the difference isn't always clearly delineated or reported when talking to journalists...
If you haven't already seen the talk recently given at the Chaos Computer Club's "Hacker Hotel" named "How Thermonuclear fusion works, free energy without waste", I highly recommend it. https://libranet.de/display/0b6b25a8-ff152736-e38872dd7aed088e