5 ms·
> Fusion ignition is the point at which a nuclear fusion reaction becomes self-sustaining. This occurs when the energy being given off by the fusion reactions h
by xixixao 5y ago
> Fusion ignition is the point at which a nuclear fusion reaction becomes self-sustaining. This occurs when the energy being given off by the fusion reactions heats the fuel mass more rapidly than various loss mechanisms cool it.
https://en.m.wikipedia.org/wiki/Fusion_ignition https://en.m.wikipedia.org/wiki/Fusion_ignition
- gremIin 5y agoHow is this any different than the term 'breakeven' [0]? > Breakeven describes the moment when plasmas in a fusion device release at least as much energy as is required to heat them [0] https://www.iter.org/sci/BeyondITER https://www.iter.org/sci/BeyondITER Is this just a case of multiple terms for the same phenomenon, and do plasma physicists have a preference?
- detaro 5y agoThe wikipedia article linked answers that.
- deleted 5y ago[deleted]
- falcrist 5y agoThat question is answered in the wikipedia link above. > Ignition should not be confused with breakeven, a similar concept that compares the total energy being given off to the energy being used to heat the fuel. The key difference is that breakeven ignores losses to the surroundings, which do not contribute to heating the fuel, and thus are not able to make the reaction self-sustaining. Breakeven is an important goal in the fusion energy field, but ignition is required for a practical energy producing design.
- AutumnCurtain 5y ago>Early reports estimated that 250 kilo-joules of energy was deposited on the target (roughly 2/3 of the energy from the beams), which resulted in a 1.3 Megajoule output from the fusing plasma. Incredible progress over where they were just a couple years ago.
- xxpor 5y agoFor reference: 1 MJ = 0.277778 kWh. Not trying to knock the progress made or anything like that, I just needed the conversion to a more familiar unit in order to appreciate what sort of scale they're talking about.
- Jensson 5y agoAlso 1 MJ = 250 calories. So like a pizza slice.
- NullPrefix 5y agocalories or kilocalories?
- ruste 5y agoWhen thinking of this amount of energy in kWh it seems small, but if this is deposited by lasers in a small fraction of a second it seems like a huge amount of power delivery.
- xxpor 5y agoYeah, the time scale and volume of where it's happening matters a lot. It's like in fission when you read about reactions giving net energy of X MeV. If you convert that to even Wh, let alone kWh, it's an incredibly small number. But when you start multiplying by the number of atoms in a fuel source, it starts adding up VERY quickly.
- deleted 5y ago[deleted]
- connicpu 5y agoThough, when 1 MJ is generated in a fraction of a second, that does mean its instantaneous output was in the MW+ range
- tsimionescu 5y agoIt should be noted that 'self sustaining' only means that the entire pellet undergoes fusion. The process still stops after a few instants of time, requiring a new pellet of fuel, a new laser burst (consuming at least twenty times the power that gets deposited in the plasma), and worst of all, a new monumentally expensive hohlraum, machined to nanometer precision.
- leephillips 5y agoGood points, but you mean energy, and it’s several hundred times.
- tsimionescu 5y agoYes, should have said energy. As for hundreds vs twenty, my understanding was that newer lasers than what NIF is using should be in the twenty times range, but you're right that at NIF they use hundreds of times more energy than they can deliver to the plasma.