7 ms·

As far as I know laser fusion is not a practical technology for energy production due to the plasma instability effects, high pellets cost (several orders of ma

by fuoqi 6y ago

As far as I know laser fusion is not a practical technology for energy production due to the plasma instability effects, high pellets cost (several orders of magnitude more than necessary for economic viability), huge reliance on a very precise calibration, and low power capacity even in optimistic scenarios. Most of the funding this field receives is motivated by checking models and constants for thermonuclear weapons. Since nuclear tests are banned, it's the easiest way to study plasma in conditions similar to those of a detonated thermonuclear bomb.

hannasanarion 6y ago
The NIF's reactor model doesn't need plasma stability, right? The article points out they're intending to use a similar principle to an internal combustion engine: put in a tiny amount of fuel, blow it up, capture the energy, repeat.
- fuoqi 6y ago
  No, it very much does. Laser fusion relies on creation of a spherically symmetric shock wave, which in turn momentarily creates huge pressure and temperature in the center of a pellet, thus igniting the fusion reaction. Any asymmetry (caused either by miscalibration, setup design, pellet flaw or even simple thermal noise) gets amplified by plasma instability effects and results in huge energy losses. The wiki article [0] briefly covers some of such effects. [0]: https://en.wikipedia.org/wiki/Inertial_confinement_fusion#Issues_with_successful_achievement https://en.wikipedia.org/wiki/Inertial_confinement_fusion#Is...
  - alexpotato 6y ago
    How does the level of precision here compare to the precision needed to design LIGO? I remember reading the precision requirements for LIGO and then reading about the efforts needed to achieve that precision and it seemed like magic. e.g. IIRC LIGO has a precision of PORTIONS of a wavelength of light at the end of arms that are kilometers long. Is the precision for plasma stability that much higher? (I understand that these are very different systems so asking more from an overall "what can we currently achieve" perspective).
    - treeman79 6y ago
      Put a rock tumbler on top of the sensors. Probably similar added difficulty.
    - raziel2701 6y ago
      It's kind of hard to compare, especially since I don't know what you mean by precision: the metrics on both projects are very different. LIGO is all about minimizing losses as the laser light bounces back and forth the two mirrors. The losses here arise from the stack of materials that the mirrors are made out of, which are multilayers of different oxides plus/minus Si or Ge, I forget. So one metric of course is the surface roughness of the material, but then there are also energetic defects called two-level systems in which atoms can absorb a little bit of light to tunnel into another location and thus contribute to the losses by having absorbed laser energy. There's coefficients of thermal expansion, stresses, that all have to be taken into account and tested as you layer all these dissimilar materials that may behave ok at room temperature but not at cryogenic ones for instance. So LIGO is a game of minimizing losses, because you're after detecting the faintest of signals: a gravitational wave. Their game is all about increasing the signal to noise ratio. NIF is a monster of energy. There's the whole steering of an enormous laser pulse which is the addition of 192 beams that have to converge into a tiny area the size of a pencil eraser. There's the containment of all this energy into a steel capsule that looks like something out of a sci-fi piece. There's the manufacture of the 2 mm diameter capsule that starts as plastic but is then coated with diamond, beryllium or more plastic and that leads to inherent asymmetries because it's not easy to coat a non-planar geometry. Already this coating assymmetry is very likely to lead to the hydrodynamic instabilities (https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instab...) that are obstructing the path forward. The hole with which you fill up the capsule with DT is still a problem, but they try to sweep it under the rug. The surface roughness of the capsule is a problem, contaminants in the diamond or plastic is a problem, a few atomic percent is enough to significantly dampen the amount of X-ray absorption/transmission. Control of the material's density is another one. The work that goes on all of this is tricky because you can solve all of these and control them very well on a planar geometry, but the moment you want to take this onto a sphere it doesn't work as well, we cannot suspend something in Earth's gravity without using a string, which then introduces an asymmetry. So the best we use is we roll the sphere around, and it's not very good for the tolerances that the scientists think we need. And NIF has a history of escalation. We are currently shooting 1.6 - 1.8 MJ, but the scientists' simulations had predicted kJ range shots in the beginning, and the estimate has continued to climb. You see it in the article itself that they're hoping to get funding to go to 3 MJ. But there are some studies (Halite-Centurion IIRC) from the 50s that showed you needed like 100 MJ to get inertial confinement fusion on a capsule, and I think we've been happily disregarding those results, because, well, politics, job-protection etc. It's a complicated story, shrouded in a lot of secrecy, so I'm glad to read that the NNSA is reviewing it. So, precision in LIGO, I don't think translates to precision in NIF. LIGO feels more like golf, NIF feels, like some beasts fighting it out. Very different set of challenges, very different resource pools they can draw from (I would argue that NIF can draw more money but less talent because of security clearance requirements restricting employees to be US citizens).
- Hizonner 6y ago
  "Capture the energy". They haven't even looked at that step. Laser fusion is about the least promising, most impractical possible approach to building a power reactor, even if you do manage to get ignition. Since at least the early 1980s, the word on the street has been that the talk about power is just a politically palatable wrapper for the weapons application. And let's just say that some of the people I heard that from, back in the 1980s, were in enough of a position to know that they probably shouldn't have said anything to some random kid like me. Not to say that there aren't a few benighted souls working on it who've managed to convince themselves it's a power source, but notice that nobody but Livermore has ever bothered to put much into inertial confinement... and Livermore is a weapons lab?
  - cbkeller 6y ago
    That's fair enough from a political perspective (after all, as they say in the article, >70% of NIF shots are going to [nuclear] stockpile stewardship now) -- but just to give NIF a bit of credit on the "basic science" front, it has turned out to be quite good for studying the properties of matter under extreme compression more generally. Some mineral physicists I know have used this to write some cool papers about the properties of natural materials at conditions replicating those expected in the cores of giant exoplanets [1-3], for example. [1] https://www.nature.com/articles/s41550-018-0437-9 https://www.nature.com/articles/s41550-018-0437-9 [2] https://doi.org/10.3389/feart.2019.00023 https://doi.org/10.3389/feart.2019.00023 [3] https://advances.sciencemag.org/content/4/4/eaao5864 https://advances.sciencemag.org/content/4/4/eaao5864
    - noobermin 6y ago
      Funny tidbit, there is a huge scramble and fight over these few shot days from different research groups across the US that can actually be used for non-nuke and non-fusion physics, they're called "Discovery Science" shots and there are only like a dozen or so each year. For example, last year 18 shot days were devoted to DS.[0] [0] https://lasers.llnl.gov/news/next-10-discovery-science-experiments-chosen https://lasers.llnl.gov/news/next-10-discovery-science-exper...
jvanderbot 6y ago
I think you just repeated most of TFA, but I appreciate the summary.
SiempreViernes 6y ago
You might enjoy this report on the NIF from 2000 when it was being reviewed because of delays and cost growth: https://web.archive.org/web/20010209102303/http://www.nrdc.org/nuclear/nif2/findings.asp https://web.archive.org/web/20010209102303/http://www.nrdc.o... Has nice quotes like: "Putting aside for a moment the vexing question of whether a "big science" machine well into the construction phase should still be plagued with numerous unresolved technology development issues, there is considerable evidence that both the science and technology underlying the NIF are not sound." and "While a large majority of ICFAC voted in May 1994 to support proceeding with engineering design of the NIF, [20] their decision was once again based on non-peer-reviewed LASNEX code predictions that had been hastily generated in the weeks immediately prior to the meeting. These calculations purported to demonstrate ignition with novel gas-filled hohlraum targets -- predictions that were subsequently not borne out by actual experiments conducted after the meeting."
- lumost 6y ago
  These big projects are great at eating budget from committees. Tons of meetings, delayed results for decades resulting in limited accountability, opportunities for everyone to be part of the picture and not point fingers at each other. Not to mention bragging rights for “leading” such large projects. We often bemoan the state of the research job market on HN. I can’t help but wonder what moving funding from these facilities to smaller experiments and research labs would do.
  - cbkeller 6y ago
    Well I think the catch is that, to use the US as an example, "big science" projects such as the NIF, particle accelerators, synchrotron light sources, and supercomputers are generally all funded by the DOE, while small individual research labs are generally funded by NSF or (if biomedical) NIH. Critically, the only reason that DOE can support the cost of these "big science" projects is that they are generally "dual use" so to speak, with both basic science and national security applications. A similar dynamic is arguably at play in the funding of the largest projects in other countries as well. So it is not clear that cutting such "big science" projects would in practice actually open up more funding for small basic science grants, lacking the same national security applications.
leephillips 6y ago
You are correct on all points. The public story is energy, the real story is more about stockpile stewardship. Since we will never derive commercial power from fusion, it would be foolish of Congress to continue to fund this sector with that in mind: http://progressive.org/op-eds/let-cut-our-losses-on-fusion-energy-180313/ http://progressive.org/op-eds/let-cut-our-losses-on-fusion-e...
- falseprofit 6y ago
  The comment you're replying to is talking about laser fusion. It would be foolish to give up on the tokamak at this point...
  - leephillips 6y ago
    Quite. I’m sure that commercial fusion power from tokomaks is only five years away, as it has been since 1949.
    - falseprofit 6y ago
      Try thinking more than 5 years ahead.
jjk166 6y ago
The NIF was never intended to produce power, but it serves as a good science experiment for understanding the challenges of inertial confinement fusion. You need to make something that works before you can make something that works better. The only fusion devices humanity has yet gotten to produce net power are thermonuclear bombs. Laser fusion tries to replicate those conditions as best as possible without detonating a fission primary. Yes, this means laser fusion is good for validating nuclear bomb models, but it's also the only route to fusion where we know for a fact that every issue is strictly an engineering problem.
- Beldin 6y ago
  The only route? What's different about ITER? If I remember correctly, they're ahead in terms of results towards energy generation.
  - jjk166 6y ago
    ITER is magnetic confinement fusion - the plasma is heated to extreme temperatures but at low density. While theoretically it looks like a much more promising route to a practical fusion reactor, as far as we know there has never been a net-positive magnetically confined fusion reaction in the universe. Plasma physics is incredibly complicated and we've run into a long series of issues with plasma instabilities, we believe that these issues will be overcome but we still can't rule out some unknown physics which renders it impossible. I personally believe tokamaks like ITER will be the route that leads to energy generation, but putting all our eggs in one basket is risky and inertial confinement experiments like NIF let us answer fundamentally different questions about reality.
noobermin 6y ago
>due to the plasma instability effects All fusion experiments are not reaching ignition due to plasma instabilities. Not exaggerating, all of them. The funding from NNSA is actually in this very article.
AtlasBarfed 6y ago
Even if sustained fusion were achieved, it has issues with degradation of the vessel/equipment from high speed neutrons? LFTR scaled down to a closet, so with "mass production" you could just replace the vessel at "reasonable cost", but these fusion facilities are massive and expensive.

by fuoqi 6y ago

hannasanarion 6y ago

The NIF's reactor model doesn't need plasma stability, right? The article points out they're intending to use a similar principle to an internal combustion engine: put in a tiny amount of fuel, blow it up, capture the energy, repeat.

fuoqi 6y ago
No, it very much does. Laser fusion relies on creation of a spherically symmetric shock wave, which in turn momentarily creates huge pressure and temperature in the center of a pellet, thus igniting the fusion reaction. Any asymmetry (caused either by miscalibration, setup design, pellet flaw or even simple thermal noise) gets amplified by plasma instability effects and results in huge energy losses. The wiki article [0] briefly covers some of such effects. [0]: https://en.wikipedia.org/wiki/Inertial_confinement_fusion#Issues_with_successful_achievement https://en.wikipedia.org/wiki/Inertial_confinement_fusion#Is...
- alexpotato 6y ago
  How does the level of precision here compare to the precision needed to design LIGO? I remember reading the precision requirements for LIGO and then reading about the efforts needed to achieve that precision and it seemed like magic. e.g. IIRC LIGO has a precision of PORTIONS of a wavelength of light at the end of arms that are kilometers long. Is the precision for plasma stability that much higher? (I understand that these are very different systems so asking more from an overall "what can we currently achieve" perspective).
  - treeman79 6y ago
    Put a rock tumbler on top of the sensors. Probably similar added difficulty.
  - raziel2701 6y ago
    It's kind of hard to compare, especially since I don't know what you mean by precision: the metrics on both projects are very different. LIGO is all about minimizing losses as the laser light bounces back and forth the two mirrors. The losses here arise from the stack of materials that the mirrors are made out of, which are multilayers of different oxides plus/minus Si or Ge, I forget. So one metric of course is the surface roughness of the material, but then there are also energetic defects called two-level systems in which atoms can absorb a little bit of light to tunnel into another location and thus contribute to the losses by having absorbed laser energy. There's coefficients of thermal expansion, stresses, that all have to be taken into account and tested as you layer all these dissimilar materials that may behave ok at room temperature but not at cryogenic ones for instance. So LIGO is a game of minimizing losses, because you're after detecting the faintest of signals: a gravitational wave. Their game is all about increasing the signal to noise ratio. NIF is a monster of energy. There's the whole steering of an enormous laser pulse which is the addition of 192 beams that have to converge into a tiny area the size of a pencil eraser. There's the containment of all this energy into a steel capsule that looks like something out of a sci-fi piece. There's the manufacture of the 2 mm diameter capsule that starts as plastic but is then coated with diamond, beryllium or more plastic and that leads to inherent asymmetries because it's not easy to coat a non-planar geometry. Already this coating assymmetry is very likely to lead to the hydrodynamic instabilities (https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instab...) that are obstructing the path forward. The hole with which you fill up the capsule with DT is still a problem, but they try to sweep it under the rug. The surface roughness of the capsule is a problem, contaminants in the diamond or plastic is a problem, a few atomic percent is enough to significantly dampen the amount of X-ray absorption/transmission. Control of the material's density is another one. The work that goes on all of this is tricky because you can solve all of these and control them very well on a planar geometry, but the moment you want to take this onto a sphere it doesn't work as well, we cannot suspend something in Earth's gravity without using a string, which then introduces an asymmetry. So the best we use is we roll the sphere around, and it's not very good for the tolerances that the scientists think we need. And NIF has a history of escalation. We are currently shooting 1.6 - 1.8 MJ, but the scientists' simulations had predicted kJ range shots in the beginning, and the estimate has continued to climb. You see it in the article itself that they're hoping to get funding to go to 3 MJ. But there are some studies (Halite-Centurion IIRC) from the 50s that showed you needed like 100 MJ to get inertial confinement fusion on a capsule, and I think we've been happily disregarding those results, because, well, politics, job-protection etc. It's a complicated story, shrouded in a lot of secrecy, so I'm glad to read that the NNSA is reviewing it. So, precision in LIGO, I don't think translates to precision in NIF. LIGO feels more like golf, NIF feels, like some beasts fighting it out. Very different set of challenges, very different resource pools they can draw from (I would argue that NIF can draw more money but less talent because of security clearance requirements restricting employees to be US citizens).
Hizonner 6y ago
"Capture the energy". They haven't even looked at that step. Laser fusion is about the least promising, most impractical possible approach to building a power reactor, even if you do manage to get ignition. Since at least the early 1980s, the word on the street has been that the talk about power is just a politically palatable wrapper for the weapons application. And let's just say that some of the people I heard that from, back in the 1980s, were in enough of a position to know that they probably shouldn't have said anything to some random kid like me. Not to say that there aren't a few benighted souls working on it who've managed to convince themselves it's a power source, but notice that nobody but Livermore has ever bothered to put much into inertial confinement... and Livermore is a weapons lab?
- cbkeller 6y ago
  That's fair enough from a political perspective (after all, as they say in the article, >70% of NIF shots are going to [nuclear] stockpile stewardship now) -- but just to give NIF a bit of credit on the "basic science" front, it has turned out to be quite good for studying the properties of matter under extreme compression more generally. Some mineral physicists I know have used this to write some cool papers about the properties of natural materials at conditions replicating those expected in the cores of giant exoplanets [1-3], for example. [1] https://www.nature.com/articles/s41550-018-0437-9 https://www.nature.com/articles/s41550-018-0437-9 [2] https://doi.org/10.3389/feart.2019.00023 https://doi.org/10.3389/feart.2019.00023 [3] https://advances.sciencemag.org/content/4/4/eaao5864 https://advances.sciencemag.org/content/4/4/eaao5864
  - noobermin 6y ago
    Funny tidbit, there is a huge scramble and fight over these few shot days from different research groups across the US that can actually be used for non-nuke and non-fusion physics, they're called "Discovery Science" shots and there are only like a dozen or so each year. For example, last year 18 shot days were devoted to DS.[0] [0] https://lasers.llnl.gov/news/next-10-discovery-science-experiments-chosen https://lasers.llnl.gov/news/next-10-discovery-science-exper...

jvanderbot 6y ago

I think you just repeated most of TFA, but I appreciate the summary.

SiempreViernes 6y ago

You might enjoy this report on the NIF from 2000 when it was being reviewed because of delays and cost growth: https://web.archive.org/web/20010209102303/http://www.nrdc.org/nuclear/nif2/findings.asp https://web.archive.org/web/20010209102303/http://www.nrdc.o... Has nice quotes like: "Putting aside for a moment the vexing question of whether a "big science" machine well into the construction phase should still be plagued with numerous unresolved technology development issues, there is considerable evidence that both the science and technology underlying the NIF are not sound." and "While a large majority of ICFAC voted in May 1994 to support proceeding with engineering design of the NIF, [20] their decision was once again based on non-peer-reviewed LASNEX code predictions that had been hastily generated in the weeks immediately prior to the meeting. These calculations purported to demonstrate ignition with novel gas-filled hohlraum targets -- predictions that were subsequently not borne out by actual experiments conducted after the meeting."

lumost 6y ago
These big projects are great at eating budget from committees. Tons of meetings, delayed results for decades resulting in limited accountability, opportunities for everyone to be part of the picture and not point fingers at each other. Not to mention bragging rights for “leading” such large projects. We often bemoan the state of the research job market on HN. I can’t help but wonder what moving funding from these facilities to smaller experiments and research labs would do.
- cbkeller 6y ago
  Well I think the catch is that, to use the US as an example, "big science" projects such as the NIF, particle accelerators, synchrotron light sources, and supercomputers are generally all funded by the DOE, while small individual research labs are generally funded by NSF or (if biomedical) NIH. Critically, the only reason that DOE can support the cost of these "big science" projects is that they are generally "dual use" so to speak, with both basic science and national security applications. A similar dynamic is arguably at play in the funding of the largest projects in other countries as well. So it is not clear that cutting such "big science" projects would in practice actually open up more funding for small basic science grants, lacking the same national security applications.

leephillips 6y ago

You are correct on all points. The public story is energy, the real story is more about stockpile stewardship. Since we will never derive commercial power from fusion, it would be foolish of Congress to continue to fund this sector with that in mind: http://progressive.org/op-eds/let-cut-our-losses-on-fusion-energy-180313/ http://progressive.org/op-eds/let-cut-our-losses-on-fusion-e...

falseprofit 6y ago
The comment you're replying to is talking about laser fusion. It would be foolish to give up on the tokamak at this point...
- leephillips 6y ago
  Quite. I’m sure that commercial fusion power from tokomaks is only five years away, as it has been since 1949.
  - falseprofit 6y ago
    Try thinking more than 5 years ahead.

jjk166 6y ago

The NIF was never intended to produce power, but it serves as a good science experiment for understanding the challenges of inertial confinement fusion. You need to make something that works before you can make something that works better. The only fusion devices humanity has yet gotten to produce net power are thermonuclear bombs. Laser fusion tries to replicate those conditions as best as possible without detonating a fission primary. Yes, this means laser fusion is good for validating nuclear bomb models, but it's also the only route to fusion where we know for a fact that every issue is strictly an engineering problem.

Beldin 6y ago
The only route? What's different about ITER? If I remember correctly, they're ahead in terms of results towards energy generation.
- jjk166 6y ago
  ITER is magnetic confinement fusion - the plasma is heated to extreme temperatures but at low density. While theoretically it looks like a much more promising route to a practical fusion reactor, as far as we know there has never been a net-positive magnetically confined fusion reaction in the universe. Plasma physics is incredibly complicated and we've run into a long series of issues with plasma instabilities, we believe that these issues will be overcome but we still can't rule out some unknown physics which renders it impossible. I personally believe tokamaks like ITER will be the route that leads to energy generation, but putting all our eggs in one basket is risky and inertial confinement experiments like NIF let us answer fundamentally different questions about reality.

noobermin 6y ago

>due to the plasma instability effects All fusion experiments are not reaching ignition due to plasma instabilities. Not exaggerating, all of them. The funding from NNSA is actually in this very article.

AtlasBarfed 6y ago

Even if sustained fusion were achieved, it has issues with degradation of the vessel/equipment from high speed neutrons? LFTR scaled down to a closet, so with "mass production" you could just replace the vessel at "reasonable cost", but these fusion facilities are massive and expensive.