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The 300 million joules to produce 2 million joules was almost entirely due to <1% efficient lasers.. even using “old” off the shelf solid state lasers with 15%

The 300 million joules to produce 2 million joules was almost entirely due to <1% efficient lasers.. even using “old” off the shelf solid state lasers with 15% efficiencies you’re already down to ~15 million joules. We’re much closer that the “300->2->3” implies. Some labs are already working with 20% efficient lasers, so hypothetically, Fusion is closer to “10->2->3” which is just amazing.

corille 4y ago
There are different kinds of lasers. Last time I checked in 2018, Nd:glass lasers were the only choice for producing short, ultra-high power laser pulses with regular beam profile. Beam profile is very important for tight focusing. They may be 80's technology but these were produced in 2005. Efficient fiber optic lasers were already available but they are not suitable for the task. https://lasers.llnl.gov/about/how-nif-works/seven-wonders/laser-glass https://lasers.llnl.gov/about/how-nif-works/seven-wonders/la...
- mikeyouse 4y ago
  So the NIF spec'ed out a replacement using a diode-pumped Yb:SFAP laser that they estimated to be 10% efficient in ~2009: https://en.wikipedia.org/wiki/Mercury_laser https://en.wikipedia.org/wiki/Mercury_laser https://www.laserfocusworld.com/test-measurement/research/article/16551380/highpower-solidstate-lasers-the-mercury-laser-moves-toward-practical-laser-fusion https://www.laserfocusworld.com/test-measurement/research/ar... The second link has more details, but they show a 0.7% efficient NIF vs. a 7% efficient Mercury laser in the tiny little chart graphic -- which would reduce the energy for this experiment from 285MJ to 28MJ. This is way outside my area of expertise, but from what I understand, the same general tech that LLNL used to generate the HAPLS for Europe's laser research could be applied to the Mercury-like lasers and increase efficiency even further. https://www.techbriefs.com/component/content/article/tb/insiders/pit/stories/45252 https://www.techbriefs.com/component/content/article/tb/insi...
  - corille 4y ago
    Thank you for interesting links. However, I see that the specified pulse energy of a single Mercury laser is 100J vs 18.7kJ for NIF so my point is still valid. There is no way to arrange 20k lasers all pointing at one pellet.
    - mikeyouse 4y ago
      That was just a prototype laser to prove the direct drive approach with a high frequency solution.. They demo'ed a suitable laser operating at 10hz vs. 0.0001HZ with the existing NIF capability. Since the 100J Mercury laser was transferring more than 10x the energy to target compared to NIF (with an obvious path to 20x) - think of this as a 1/20th scale replacement for a single NIF beam with the ability to fire multiple shots per second. Even if they couldn't increase the power past 100J (which they certainly can), using 2,000 beams instead of 192 doesn't seem too difficult given the much smaller overall energy and heat-removal requirements.
Vt71fcAqt7 4y ago
Can you point me to somewhere to read more about this? Also from wikipedia: "NIF hosts the world's most energetic laser."[0] Is that true and if so can many less powerful but more efficient lasers make up for it? [0]https://en.wikipedia.org/wiki/National_Ignition_Facility# https://en.wikipedia.org/wiki/National_Ignition_Facility#
- mikeyouse 4y ago
  The total energy consumed isn't what these places are optimizing for. LLNL/NIF "invented" a lot of this research so their facility is the most energetic but also ~the least efficient, while being the most important in the world. When they constructed their laser facility in 1996, NIF used the surest-bet laser system acknowledging that hypothetical competing systems could be better suited (solid state lasers were just coming into play at the time due to semiconductor manufacturing). They've done a massive amount of work ramp up the power and get their <0.5% system to ~0.7% efficient (power from the wall:power hitting the target). The NIF facility uses "indirect drive" where the energy from the lasers are first converted to xrays, and then the fuel is energized with the xrays. Not coincidentally, that's the exact mechanism that modern nuclear warheads use to drive their fusion stage -- so NIF's selection here makes even more sense given their DOD funding and 'stockpile stewardship' mission statement. Since a lot of modern laser research now overlaps with advanced semiconductor manufacturing, the competing systems are now much more mature. Here's a good rundown, but experts think that it's plausible to use even up to 20% efficient systems. Rather than using the laser to first generate xrays - these "direct drive" systems deposit the energy from the lasers directly on the pellets. https://physicstoday.scitation.org/do/10.1063/pt.6.2.20211020a/full/ https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...

corille 4y ago

There are different kinds of lasers. Last time I checked in 2018, Nd:glass lasers were the only choice for producing short, ultra-high power laser pulses with regular beam profile. Beam profile is very important for tight focusing. They may be 80's technology but these were produced in 2005. Efficient fiber optic lasers were already available but they are not suitable for the task. https://lasers.llnl.gov/about/how-nif-works/seven-wonders/laser-glass https://lasers.llnl.gov/about/how-nif-works/seven-wonders/la...

mikeyouse 4y ago
So the NIF spec'ed out a replacement using a diode-pumped Yb:SFAP laser that they estimated to be 10% efficient in ~2009: https://en.wikipedia.org/wiki/Mercury_laser https://en.wikipedia.org/wiki/Mercury_laser https://www.laserfocusworld.com/test-measurement/research/article/16551380/highpower-solidstate-lasers-the-mercury-laser-moves-toward-practical-laser-fusion https://www.laserfocusworld.com/test-measurement/research/ar... The second link has more details, but they show a 0.7% efficient NIF vs. a 7% efficient Mercury laser in the tiny little chart graphic -- which would reduce the energy for this experiment from 285MJ to 28MJ. This is way outside my area of expertise, but from what I understand, the same general tech that LLNL used to generate the HAPLS for Europe's laser research could be applied to the Mercury-like lasers and increase efficiency even further. https://www.techbriefs.com/component/content/article/tb/insiders/pit/stories/45252 https://www.techbriefs.com/component/content/article/tb/insi...
- corille 4y ago
  Thank you for interesting links. However, I see that the specified pulse energy of a single Mercury laser is 100J vs 18.7kJ for NIF so my point is still valid. There is no way to arrange 20k lasers all pointing at one pellet.
  - mikeyouse 4y ago
    That was just a prototype laser to prove the direct drive approach with a high frequency solution.. They demo'ed a suitable laser operating at 10hz vs. 0.0001HZ with the existing NIF capability. Since the 100J Mercury laser was transferring more than 10x the energy to target compared to NIF (with an obvious path to 20x) - think of this as a 1/20th scale replacement for a single NIF beam with the ability to fire multiple shots per second. Even if they couldn't increase the power past 100J (which they certainly can), using 2,000 beams instead of 192 doesn't seem too difficult given the much smaller overall energy and heat-removal requirements.

Vt71fcAqt7 4y ago

Can you point me to somewhere to read more about this? Also from wikipedia: "NIF hosts the world's most energetic laser."[0] Is that true and if so can many less powerful but more efficient lasers make up for it? [0]https://en.wikipedia.org/wiki/National_Ignition_Facility# https://en.wikipedia.org/wiki/National_Ignition_Facility#

mikeyouse 4y ago
The total energy consumed isn't what these places are optimizing for. LLNL/NIF "invented" a lot of this research so their facility is the most energetic but also ~the least efficient, while being the most important in the world. When they constructed their laser facility in 1996, NIF used the surest-bet laser system acknowledging that hypothetical competing systems could be better suited (solid state lasers were just coming into play at the time due to semiconductor manufacturing). They've done a massive amount of work ramp up the power and get their <0.5% system to ~0.7% efficient (power from the wall:power hitting the target). The NIF facility uses "indirect drive" where the energy from the lasers are first converted to xrays, and then the fuel is energized with the xrays. Not coincidentally, that's the exact mechanism that modern nuclear warheads use to drive their fusion stage -- so NIF's selection here makes even more sense given their DOD funding and 'stockpile stewardship' mission statement. Since a lot of modern laser research now overlaps with advanced semiconductor manufacturing, the competing systems are now much more mature. Here's a good rundown, but experts think that it's plausible to use even up to 20% efficient systems. Rather than using the laser to first generate xrays - these "direct drive" systems deposit the energy from the lasers directly on the pellets. https://physicstoday.scitation.org/do/10.1063/pt.6.2.20211020a/full/ https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...