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Exactly. Looking at the Wikipedia article [1] suggest that they start out with 422 MJ stored in capacitors, turn this into 4 MJ IR laser light, convert it into

Exactly. Looking at the Wikipedia article [1] suggest that they start out with 422 MJ stored in capacitors, turn this into 4 MJ IR laser light, convert it into 1.8 MJ UV laser light, this into x-rays of which 0.15 MJ heat the target of which finally 0.015 MJ heat the fuel. Depending on what in this chain you consider the input energy, you can get orders of magnitude different numbers - 15 kJ of energy produced could either be a gain of 1 or a gain of ‭0.0000036 or anything in between.‬ And this is before trying to capture the released energy and converting it into electricity, this will come with another sizable loss. [1] https://en.wikipedia.org/wiki/National_Ignition_Facility https://en.wikipedia.org/wiki/National_Ignition_Facility

est31 4y ago
From https://www.ft.com/content/4b6f0fab-66ef-4e33-adec-cfc345589dc7 https://www.ft.com/content/4b6f0fab-66ef-4e33-adec-cfc345589... > The fusion reaction at the US government facility produced about 2.5 megajoules of energy, which was about 120 per cent of the 2.1 megajoules of energy in the lasers, the people with knowledge of the results said, adding that the data was still being analysed. They probably upgraded the rig since the Wikipedia article was written, so most likely the 2.1 MJ refers to the UV light numbers.
- danbruc 4y ago
  If this is assumption is true, they only produced 0.6 % of the energy they spent. Another question would then be, how relevant this is, i.e. could the UV light be produced much more efficiently than the experiment does? Maybe some constraints forces them to use a very inefficient process? In that case it might be reasonable to use the UV laser power as the reference for the gain.
  - kelnos 4y ago
    Sure, and if they upgrade the lasers themselves to current laser tech (as I understand it, the NIF's hardware is around 25 years out of date on that front), then that 0.6% number probably jumps to 20% or so. Which still isn't enough, but is way closer than 0.6%. Add to that the fact that improvements in laser efficiency is a hot research area (as lasers are used commercially in a lot of places, and cost-cutting is always a concern), and this is starting to feel a little more attainable.
  - willis936 4y ago
    I think the more interesting question is "how does this scale with more laser power?" Even if the lasers are 1% efficient does it matter if 100 GJ of electrical power results in 100 TJ of fusion heat? I'm not saying this is at all how it scales, but it is the logic behind pursuing an ICF power plant. The fuel gets ignited and heats itself. Also, for fun, 100 TJ is 24 kT TNT equivalent: slightly more than the bombs dropped on Hiroshima and Nagasaki. Trying to capture this energy released instantaneously would be a fun engineering challenge.

est31 4y ago

From https://www.ft.com/content/4b6f0fab-66ef-4e33-adec-cfc345589dc7 https://www.ft.com/content/4b6f0fab-66ef-4e33-adec-cfc345589... > The fusion reaction at the US government facility produced about 2.5 megajoules of energy, which was about 120 per cent of the 2.1 megajoules of energy in the lasers, the people with knowledge of the results said, adding that the data was still being analysed. They probably upgraded the rig since the Wikipedia article was written, so most likely the 2.1 MJ refers to the UV light numbers.

danbruc 4y ago
If this is assumption is true, they only produced 0.6 % of the energy they spent. Another question would then be, how relevant this is, i.e. could the UV light be produced much more efficiently than the experiment does? Maybe some constraints forces them to use a very inefficient process? In that case it might be reasonable to use the UV laser power as the reference for the gain.
- kelnos 4y ago
  Sure, and if they upgrade the lasers themselves to current laser tech (as I understand it, the NIF's hardware is around 25 years out of date on that front), then that 0.6% number probably jumps to 20% or so. Which still isn't enough, but is way closer than 0.6%. Add to that the fact that improvements in laser efficiency is a hot research area (as lasers are used commercially in a lot of places, and cost-cutting is always a concern), and this is starting to feel a little more attainable.
- willis936 4y ago
  I think the more interesting question is "how does this scale with more laser power?" Even if the lasers are 1% efficient does it matter if 100 GJ of electrical power results in 100 TJ of fusion heat? I'm not saying this is at all how it scales, but it is the logic behind pursuing an ICF power plant. The fuel gets ignited and heats itself. Also, for fun, 100 TJ is 24 kT TNT equivalent: slightly more than the bombs dropped on Hiroshima and Nagasaki. Trying to capture this energy released instantaneously would be a fun engineering challenge.