15 ms·

The Truth About Nuclear Fusion Q Factors

90 points by terryf 5y ago

mdorazio 5y ago
Can anyone comment on the heat > electricity conversion ratio? My understanding has been that modern multi-stage steam turbines used in power plants are around 90% efficient, not 50%. I might be missing other energy losses along the way, though.
- zardo 5y ago
  I don't think so, checking Siemens they're touting a 65% efficient 600MW turbine. The higher number might be including some application for the waste heat.
- Robin_Message 5y ago
  Carnot's law is what you want. Max efficiency is temperature differential divided by hot absolute temperature. So, with super heated steam of say 600 degrees C, I'd make that a maximum of about 66% theoretical, so 50% actual sounds pretty good. If you could build a plasma heat engine, you could get near 100% but I've no idea what that would technically look like.
  - nine_k 5y ago
    You can likely harvest a little bit more by using a lower temperature differential in another step, using, say, substances that boil at room temperature, to cool the water after it condenses and cannot produce work by expansion.
- phkahler 5y ago
  >> Can anyone comment on the heat > electricity conversion ratio? My understanding has been that modern multi-stage steam turbines used in power plants are around 90% efficient, not 50%. They probably mean 90% of a theoretical maximum. For example, one of the results that stood out to me in thermodynamics class was that the maximum possible efficiency of an internal combustion engine (I forget which cycle) was a function of the compression ratio. In other words you could never reach 100% conversion of chemical energy to mechanical energy and the theoretical "efficiency" was a function that increased with compression ratio but could never reach 100 percent. So lets assume an engine with a given compression ratio could have a theoretical efficiency of 50 percent, but a real-world design only achieved 45 percent. Someone might say 45/50 is 0.9 or 90 percent of the theoretical limit. That's a measure of how good the design was vs what's theoretically possible, but it has little to do with the actual efficiency of the energy conversion. IIRC the best heat-to-mechanical energy conversion devices are rockets with a theoretical efficiency of 50% but it's been half my life since I studied thermodynamics, so maybe I'm off on some of this.
  - pfdietz 5y ago
    The maximum theoretical efficiency of ideal rocket engines is much higher than 50%. At very high expansion ratio in vacuum the gas can become so cold it condenses, so almost all the internal energy of the initial hot gas will have been converted to jet kinetic energy.
    - nine_k 5y ago
      Won't you need a colossal nozzle to actually harvest these last bits of energy?
      - pfdietz 5y ago
        You need a very high area ratio (nozzle exit area/nozzle throat area), but that's possible in vacuum, especially if your thrust requirements are modest.
aaronblohowiak 5y ago
ITER isnt meant to have Q-total > 1 though, it is meant as an experimental platform not energy generation. I wonder if the author has similar thoughts on promise for smaller reactors that take advantage of HTSC magnets.. should they have an easier time achieving breakeven Q-total?
- jeffreyrogers 5y ago
  Her point is that almost all coverage of fusion elides the difference between Q-total and Q-plasma. I didn't know how big the difference was until reading her article and I'm guessing almost no one else does either.
- beezle 5y ago
  Her point is that the "Q" that has been used to sell ITER leads the public and policy makers to believe it is Q-Total, not Q-Plasma.
  - pfdietz 5y ago
    And beyond Q-Total is ROI: the ratio of $ in to $ out. An ignited fusion reactor with very high Q could very well still be below economic breakeven.
- ben_w 5y ago
  > should they have an easier time achieving breakeven Q-total? I believe that’s why they’re being made: Q being a function of both physical size and magnetic field strength, and the new superconductors being useful for increasing the latter so the former can be reduced. But I have no idea if any of them are currently attempting Q_total > 1 or not: too much hopeful PR for me to know what stage they’re really at.
  - hamburglar 5y ago
    How could they possibly be attempting Q-total > 1 when they aren’t even near Q-plasma = 1 yet? If the gain of the system overall is greater than Q-plasma, you’ve invented some other energy source in there somewhere and should throw away your reactor and focus on that thing. :D
SubiculumCode 5y ago
Fusion research is fundamentally good research to pursue, and vigorously. But in terms of energy for the world, we just happen to have an already made fusion plant some 92 million miles away. Its just an engineering problem of how to get more of it's wasted energy onto the earth using space solar arrays (Only one one-billionth of the Sun's total energy output actually reaches the Earth, now, per a google search...which seems too high, honestly).
- tsimionescu 5y ago
  Space solar arrays would be the perfect solution if we needed the energy in space. Since we need it on Earth, and since the sun is already sending exactly that energy to Earth, they are almost entirely pointless.
  - tuatoru 5y ago
    In fact, space sunshades would be much more useful to us at this point than space PV.
- causi 5y ago
  Its just an engineering problem of how to get more of it's wasted energy onto the earth using space solar arrays Considering even the best solar panels have under 50% efficiency, increasing the total solar radiation to earth would be very bad for the climate.
  - goodpoint 5y ago
    Actually it's true that increasing the overall input of energy in the planet atmosphere is bad. Yet, this also happens with nuclear, coal, gas, oil... The only solution is to capture the energy that is already being received from the sun in order to prevent it from heating up the atmosphere on site. E.g. solar panels on the desert and wind turbines
    - orthecreedence 5y ago
cyberpsybin 5y ago
Why will nuclear fusion scientists bother with anything other than Qplasma. Heat to electricity is separate problem.
- jkelleyrtp 5y ago
  Things like the NIF also have power losses in feeding the ignition. The NIF lasers are maybe .1% efficient, or less, meaning that even if energy delivered by the lasers is less than created by the reaction, it must deliver a 1000x power output just for lasers to be break-even.
- beezle 5y ago
  Because the ultimate goal is a power plant, not just a paper saying that Q-Plasma of 1 (or 10) has been reached.
- MobiusHorizons 5y ago
  I can imagine it would be reasonable for fusion scientists to not spend effort on the Heat -> electricity part. What I think the article is highlighting is that they are currently totally ignoring all the energy that goes into anything other than plasma, (ie the power to run magnets, vacuum pumps, or lasers), which from the examples given is on the order of 10s-100s of times the power delivered to the plasma. This energy should be considered by fusion scientists, because it may end up invalidating certain topologies that can achieve a Qplasma > 1, but can't achieve a Qtotal > 1. For instance from the article, it seems like pulsed lasers are relatively inefficient at turning input energy into laser energy, which might mean they would need a QPlasma > 100 before QTotal aproaches 1. I don't know which of those inefficiencies are deemed to be fundamental and which are potentially improveable, but it could suggest the whole line of research is not worth perusing.
  - willis936 5y ago
    Qtotal doesn't affect the physics of the plasma. Qplasma does. Making a machine that burns plasma is expensive. Actually understanding burning plasma is necessary to build a reactor. This basic understanding appears to be lost on Sabine.
PicassoCTs 5y ago
I have a question, i ve read a book recommended on here, about fusion, called the "The Future of Fusion Energy". (It was very good, can recommend for a general topic overview and history of progress). But i do not understand the general approach to plasma-vessel construction, in particular, why it is so passive. Its either "bend" to orbital shape dicated by the plasma physics properties when constructing (Wendelstein, Stellerators etc.). Or increase the containment vessels magnetic field strength (scaling up the reactor, high-temperature-superconductors) until it is capable to hold all the chaotic increasing fluctuation inside no matter what. My Question: Is there not a more active, not brute force approach for containing the plasma? Sort of "Whack-The-mole" countering the escape-events as they happen in a Tokamak? If i understood correctly, the system adds to itself constantly energy (its a reactor after all) and any chaotic butterfly wing flapping on the plasma current can shape up to a tornado breaching the containment and ending fusion.
- kryptn 5y ago
  > Is there not a more active, not brute force approach for containing the plasma? I think General Fusion's approach is interesting, they're compressing the plasma with a liquid metal wall.
- hamburglar 5y ago
  There is a fusion startup called CT Fusion that has an innovation in this vein: [warning: not a plasma physicist, this is just what I understand from talking to actual physics nerds who follow this] instead of using giant magnets for plasma confinement, they are using a continuously variable magnetic field that is provided by helical coils surrounding the plasma. By monitoring the shape of the surface of the plasma and varying the electrical input to the coils, playing whack-a-mole as you put it with the shape of the plasma.
  - moogly 5y ago
    ITER has/will have a multitude of different control systems to control the inherently unruly plasma too. As I understand it, any tokamak will have to do something like that. https://www.iter.org/newsline/-/3297 https://www.iter.org/newsline/-/3297
Invictus0 5y ago
I would be interested in reading a broader analysis of how scientists and other experts are misleading the public. I imagine there is enough on this subject to write a book. My layman's perspective is that it seems to follow from the belief that the public cannot understand the scientists' preferred decision, and that therefore the scientists must mislead the public "for their own good". The obvious example of course is the health authorities misleading the public on masks early on so that hospitals would be able to stockpile supplies, but I'd like to see even more places where the narrative is being twisted.
- beezle 5y ago
  An honest assesment acknowledges that current fusion research, like string theory and even HEP, has become an employment program. You can tell this is the case when 1) no efforts are made to change course once it is clear the current dogma is impractical, unprovable or lends increasingly marginal gains in knowledge at extreme cost; and 2) any who question the accepted view are shouted down and pushed aside. That is not to say there should be no money spent on researching fusion or the standard model (or beyond). Just that the current system does a poor job of allocating limited funds by putting most of the monies in one basket until well after other ideas/technologies should be given time of day and ample funding.
anonymousiam 5y ago
It's a valid point that ITER will not produce net power, but it's still a big step forward. Years ago I worked for a brilliant physicist who believed (usually correctly) that any factor less than an order of magnitude was just an "engineering problem".
- Invictus0 5y ago
  Did you read TFA? The author is not arguing that it's not worthwhile to fund fusion research; she's arguing against the misleading discourse surrounding it. "But it's still a step forward" is exactly the reason that science is misleading the public.
  - anonymousiam 5y ago
    Yes. I RTFA and saw that. I was not disagreeing with her.
- pfdietz 5y ago
  Unfortunately for that viewpoint, the power density of a DT fusion reactor is at least an order of magnitude worse than commercial fission reactors. PWR reactor vessel = 20 MW/m^3, ITER = 0.05 MW/m^3, ARC = 0.5 MW/m^3.
2OEH8eoCRo0 5y ago
Commonwealth Fusion expects to start commercialization in 2025. They say it will put power onto the grid.
- hamburglar 5y ago
  What I’ve heard is that they will have a demonstration of “net energy” by 2025. This is still a long way from solving the engineering problem of putting energy on the grid. And if that “net energy” definitions is actually Q-plasma as this video claims, it’s a lot farther still.
  - hobscoop 5y ago
    SPARC is aiming for Q_plasma of about 10 in 2025, but not to generate energy at all: it doesn't have any of the required 'blanket' system for breeding tritium. SPARC is a physics test, to make sure our theories of burning plasma are correct and to test the stability of these high field tokamaks. ITER is (among other things) supposed to be a physics test, but won't come until 2035. So SPARC's goal is to 'leapfrog' that by 10 years. You're right that there's a lot of work to be done between Q_plasma = 10 and generating energy. A lot of this work on the materials side, to engineer materials that can last for years in a fusion reactor environment.
- dr_orpheus 5y ago
  "This HTS magnet technology will next be used in SPARC, which is under construction in Devens, Massachusetts and on track to demonstrate net energy from fusion by 2025. SPARC will pave the way for the first commercially viable fusion power plant called ARC." [0] But this does not say that they are going to put power on the grid in 2025. They say net energy from fusion by 2025 which may just mean Q-plasma > 1, it does not say (which kind of proves the point of the article). They don't have any estimates of an on the grid fusion plant. https://cfs.energy/news-and-media/cfs-commercial-fusion-power-with-hts-magnet https://cfs.energy/news-and-media/cfs-commercial-fusion-powe...
  - gene-h 5y ago
sb1752 5y ago
Good documentary on Iter's claims by investigative journalist, Steve Krivit. https://www.youtube.com/watch?v=xnikAFWDhNw https://www.youtube.com/watch?v=xnikAFWDhNw Shows that the public claims are not just an exaggeration but outright fraud for the purpose of getting more funding. It's one thing to say that the purpose is experimental research, it's another entirely to claim that it will produce net energy, which is not backed any evidence or even a reasonable scientific analysis. There's a long history of fraud in fusion research, it's really important the public is well educated on the history here.
- deleted 5y ago
  [deleted]
mcwone 5y ago
Let not forget the total energy input it takes to construct the ITER project . We should not be wasting finite resources on this project.
- m0zg 5y ago
  The relatively minuscule resources "wasted" on this project could eventually solve the "climate crisis" in one fell swoop via delivering nearly inexhaustible sources of clean energy. So inexhaustible, in fact, that we could reduce CO2 by entirely engineering-driven (rather than ineffectual policy) means. And fusion would do so while also _increasing_ not _reducing_ everyone's standard of living. You could even use your gas guzzler still, by making gas from CO2 and water, and it'd be "carbon neutral" even if it belches a column of black smoke straight into the air. And this gas would be like 50 cents a gallon, too. I'd rather spend a trillion on fusion and get it done Manhattan project style than continue droning children in Afghanistan or funding $3.5T in pork barrel bullshit here at home. Just drown it in money completely until it's done. Put the very best people on it and let them have at it for real. We've done it before, several times, it worked. There's no reason why it wouldn't work this time. If there is any 21st century "Moon landing" type goal, this is it, and the United States is still best positioned to accomplish something of this magnitude. For how long that will be true I do not know, but it is true now.
  - pfdietz 5y ago
    ITER has zero chance of solving the climate crisis. Anything derived from it will be far too large, expensive, and late.
    - m0zg 5y ago
      I'm not even talking about ITER here. Let them have their own nice European pork barrel boondoggle, though I'd point out that even if it fails miserably, it's still generating valuable science and technological capabilities that cannot be generated or sustained any other way, so it's not a "waste of resources". We're talking about these projects as if they'd offer marginal, rather than _radical_ improvements in our situation, which is simply not true. If this is done this will completely upend the world and make it a better place - there's no doubt in my mind on this whatsoever. This is the _only_ environmental thing I wouldn't mind paying more taxes for, but I'd argue we don't even need that - we just need to look a little bit ahead and allocate existing resources towards longer term, riskier things benefits from which we _know_ will absolutely dwarf the investment. The reason why this is not happening is because we have trillions of dollars flowing into other troughs from which everyone involved is used to feeding. Until we disrupt those arrangements somehow our only chance of solving this is private sector investment, but private sector can't sustain things of this magnitude over an extended period of time. Not unless Musk gets involved.
tuatoru 5y ago
This is what I like about scientists, they can change their minds based on the evidence. Well done, Sabine!
- anonporridge 5y ago
  To be fair though, I don't believe Sabine is involved in any nuclear fusion research, so changing her mind on this doesn't necessarily put her own funding at risk. Changing your mind is easy when your next meal doesn't depend on continuing to believe something. In fact, she might even stand to gain if funding gets diverted from fusion research towards other projects.
  - willis936 5y ago
    If she was then she would have realized how ridiculous it is to directly compare Q performance between MCF and ICF machines, using Q as the metric to track progress, and not once uttering the words "triple product". This piece has about as much investigation as I put into the doneness of my toast.
    - kilotaras 5y ago
      Can you expand on that? I find the claim almost trivially true: we care about electricity production, so that should be the main goal we're tracking.
      - willis936 5y ago
        A high Q machine is expensive. It's by nature a nuclear facility, which adds a few zeroes to the cost. Nuclear fusion machines needs tritium fuel, which is made in exactly one breeder on the planet. In general a fusion machine just being nuclear doesn't add much scientific value. The plasma physics for making a better (cheaper) reactor has been pushed in smaller machines, as shown by better triple product values and empirical scaling laws. Triple product is a measure of how well the plasma is confined. That's the metric to focus on (when accounting for the fact that the science machines are small with scaling laws). In that regard, we have made excellent progress. A high Q machine (such as ITER) is valuable because it lets us study burning plasmas. It's an expensive pill to swallow but an essential step towards making a real reactor. Qtotal = 1 is a nothingburher. Qplasma = 1 is also a nothingburger, but at least going past that barrier grants new knowledge.
AlbertCory 5y ago
If you haven't read Sabine Hossenfelder, you should check out her other work. She is pretty acerbic about the politics of Big Physics.
- willis936 5y ago
  One should be able to tell from her bad faith implications without grasping the basics of the field.
  - AlbertCory 5y ago
    what are her "bad faith implications" ?
    - willis936 5y ago
      That the physicists are deceiving the public. She's made a narrative around fusion progress without understanding fusion progress.
ufmace 5y ago
As I understand it, the bigger problem around fusion that we're still working towards fixing is being able to maintain an actively fusioning plasma. All of these Q measurements are around very short runs, sub-second I think. ITER seems to have a goal of 400-second runs, which sounds more like it. Once we have enough understanding of plasma physics and confining magnet behavior, it will hopefully be more straightforward to optimize the energy going into the plasma, and the energy going into the magnets and cooling system, etc to hopefully achieve a QTotal > 1. And maybe have enough heat being generated that it'll be necessary and reasonable to attach a boiler to it, hook it up to a steam turbine and generator, and make some electricity.
- zardo 5y ago
  W7-X was supposed to demonstrate a 30-minute run in 2021, but that's been pushed back a year.
  - willis936 5y ago
    Mostly because of the you-know-what. W7-X is not a tokamak nor a nuclear machine. It's designed to run all day and no one on the planet doubts it. The upgrade to get it to 30 minute pulses is primarily to the heat dissipation subsystem. The ECRH subsystem of W7-X is eyewateringly beautiful.
mchusma 5y ago
I think the gap is not as far as the author purports. I've followed fusion research as a layperson for years, and clearly understand the point of these designs is to prove the most meaningful piece of the process of generating energy, not actually doing it, and that it would be a lot more work going from here to there. It think the summary on fusion is: - it's the most amazing energy source we have lined up in the mid term -ots almost certainly going to work - we are making meaningful but slower progress than we would like - it's dramatically underfunded
- pfdietz 5y ago
  My thinking on fusion is quite different. It's a technology that used to be considered the default future, but never made a lot of practical sense when examined closely, and now the justification for continuing to pursue it is becoming increasingly threadbare. In a decade or so this will become impossible for even fusion supporters to deny as the alternatives crash in cost.

90 points by terryf 5y ago

Can anyone comment on the heat > electricity conversion ratio? My understanding has been that modern multi-stage steam turbines used in power plants are around 90% efficient, not 50%. I might be missing other energy losses along the way, though.

zardo 5y ago
I don't think so, checking Siemens they're touting a 65% efficient 600MW turbine. The higher number might be including some application for the waste heat.
Robin_Message 5y ago
Carnot's law is what you want. Max efficiency is temperature differential divided by hot absolute temperature. So, with super heated steam of say 600 degrees C, I'd make that a maximum of about 66% theoretical, so 50% actual sounds pretty good. If you could build a plasma heat engine, you could get near 100% but I've no idea what that would technically look like.
- nine_k 5y ago
  You can likely harvest a little bit more by using a lower temperature differential in another step, using, say, substances that boil at room temperature, to cool the water after it condenses and cannot produce work by expansion.
phkahler 5y ago
>> Can anyone comment on the heat > electricity conversion ratio? My understanding has been that modern multi-stage steam turbines used in power plants are around 90% efficient, not 50%. They probably mean 90% of a theoretical maximum. For example, one of the results that stood out to me in thermodynamics class was that the maximum possible efficiency of an internal combustion engine (I forget which cycle) was a function of the compression ratio. In other words you could never reach 100% conversion of chemical energy to mechanical energy and the theoretical "efficiency" was a function that increased with compression ratio but could never reach 100 percent. So lets assume an engine with a given compression ratio could have a theoretical efficiency of 50 percent, but a real-world design only achieved 45 percent. Someone might say 45/50 is 0.9 or 90 percent of the theoretical limit. That's a measure of how good the design was vs what's theoretically possible, but it has little to do with the actual efficiency of the energy conversion. IIRC the best heat-to-mechanical energy conversion devices are rockets with a theoretical efficiency of 50% but it's been half my life since I studied thermodynamics, so maybe I'm off on some of this.
- pfdietz 5y ago
  The maximum theoretical efficiency of ideal rocket engines is much higher than 50%. At very high expansion ratio in vacuum the gas can become so cold it condenses, so almost all the internal energy of the initial hot gas will have been converted to jet kinetic energy.
  - nine_k 5y ago
    Won't you need a colossal nozzle to actually harvest these last bits of energy?
    - pfdietz 5y ago
      You need a very high area ratio (nozzle exit area/nozzle throat area), but that's possible in vacuum, especially if your thrust requirements are modest.

aaronblohowiak 5y ago

ITER isnt meant to have Q-total > 1 though, it is meant as an experimental platform not energy generation. I wonder if the author has similar thoughts on promise for smaller reactors that take advantage of HTSC magnets.. should they have an easier time achieving breakeven Q-total?

jeffreyrogers 5y ago
Her point is that almost all coverage of fusion elides the difference between Q-total and Q-plasma. I didn't know how big the difference was until reading her article and I'm guessing almost no one else does either.
beezle 5y ago
Her point is that the "Q" that has been used to sell ITER leads the public and policy makers to believe it is Q-Total, not Q-Plasma.
- pfdietz 5y ago
  And beyond Q-Total is ROI: the ratio of $ in to $ out. An ignited fusion reactor with very high Q could very well still be below economic breakeven.
ben_w 5y ago
> should they have an easier time achieving breakeven Q-total? I believe that’s why they’re being made: Q being a function of both physical size and magnetic field strength, and the new superconductors being useful for increasing the latter so the former can be reduced. But I have no idea if any of them are currently attempting Q_total > 1 or not: too much hopeful PR for me to know what stage they’re really at.
- hamburglar 5y ago
  How could they possibly be attempting Q-total > 1 when they aren’t even near Q-plasma = 1 yet? If the gain of the system overall is greater than Q-plasma, you’ve invented some other energy source in there somewhere and should throw away your reactor and focus on that thing. :D

SubiculumCode 5y ago

Fusion research is fundamentally good research to pursue, and vigorously. But in terms of energy for the world, we just happen to have an already made fusion plant some 92 million miles away. Its just an engineering problem of how to get more of it's wasted energy onto the earth using space solar arrays (Only one one-billionth of the Sun's total energy output actually reaches the Earth, now, per a google search...which seems too high, honestly).

tsimionescu 5y ago
Space solar arrays would be the perfect solution if we needed the energy in space. Since we need it on Earth, and since the sun is already sending exactly that energy to Earth, they are almost entirely pointless.
- tuatoru 5y ago
  In fact, space sunshades would be much more useful to us at this point than space PV.
causi 5y ago
Its just an engineering problem of how to get more of it's wasted energy onto the earth using space solar arrays Considering even the best solar panels have under 50% efficiency, increasing the total solar radiation to earth would be very bad for the climate.
- goodpoint 5y ago
  Actually it's true that increasing the overall input of energy in the planet atmosphere is bad. Yet, this also happens with nuclear, coal, gas, oil... The only solution is to capture the energy that is already being received from the sun in order to prevent it from heating up the atmosphere on site. E.g. solar panels on the desert and wind turbines
  - orthecreedence 5y ago

cyberpsybin 5y ago

Why will nuclear fusion scientists bother with anything other than Qplasma. Heat to electricity is separate problem.

jkelleyrtp 5y ago
Things like the NIF also have power losses in feeding the ignition. The NIF lasers are maybe .1% efficient, or less, meaning that even if energy delivered by the lasers is less than created by the reaction, it must deliver a 1000x power output just for lasers to be break-even.
beezle 5y ago
Because the ultimate goal is a power plant, not just a paper saying that Q-Plasma of 1 (or 10) has been reached.
MobiusHorizons 5y ago
I can imagine it would be reasonable for fusion scientists to not spend effort on the Heat -> electricity part. What I think the article is highlighting is that they are currently totally ignoring all the energy that goes into anything other than plasma, (ie the power to run magnets, vacuum pumps, or lasers), which from the examples given is on the order of 10s-100s of times the power delivered to the plasma. This energy should be considered by fusion scientists, because it may end up invalidating certain topologies that can achieve a Qplasma > 1, but can't achieve a Qtotal > 1. For instance from the article, it seems like pulsed lasers are relatively inefficient at turning input energy into laser energy, which might mean they would need a QPlasma > 100 before QTotal aproaches 1. I don't know which of those inefficiencies are deemed to be fundamental and which are potentially improveable, but it could suggest the whole line of research is not worth perusing.
- willis936 5y ago
  Qtotal doesn't affect the physics of the plasma. Qplasma does. Making a machine that burns plasma is expensive. Actually understanding burning plasma is necessary to build a reactor. This basic understanding appears to be lost on Sabine.

PicassoCTs 5y ago

I have a question, i ve read a book recommended on here, about fusion, called the "The Future of Fusion Energy". (It was very good, can recommend for a general topic overview and history of progress). But i do not understand the general approach to plasma-vessel construction, in particular, why it is so passive. Its either "bend" to orbital shape dicated by the plasma physics properties when constructing (Wendelstein, Stellerators etc.). Or increase the containment vessels magnetic field strength (scaling up the reactor, high-temperature-superconductors) until it is capable to hold all the chaotic increasing fluctuation inside no matter what. My Question: Is there not a more active, not brute force approach for containing the plasma? Sort of "Whack-The-mole" countering the escape-events as they happen in a Tokamak? If i understood correctly, the system adds to itself constantly energy (its a reactor after all) and any chaotic butterfly wing flapping on the plasma current can shape up to a tornado breaching the containment and ending fusion.

kryptn 5y ago
> Is there not a more active, not brute force approach for containing the plasma? I think General Fusion's approach is interesting, they're compressing the plasma with a liquid metal wall.
hamburglar 5y ago
There is a fusion startup called CT Fusion that has an innovation in this vein: [warning: not a plasma physicist, this is just what I understand from talking to actual physics nerds who follow this] instead of using giant magnets for plasma confinement, they are using a continuously variable magnetic field that is provided by helical coils surrounding the plasma. By monitoring the shape of the surface of the plasma and varying the electrical input to the coils, playing whack-a-mole as you put it with the shape of the plasma.
- moogly 5y ago
  ITER has/will have a multitude of different control systems to control the inherently unruly plasma too. As I understand it, any tokamak will have to do something like that. https://www.iter.org/newsline/-/3297 https://www.iter.org/newsline/-/3297

Invictus0 5y ago

I would be interested in reading a broader analysis of how scientists and other experts are misleading the public. I imagine there is enough on this subject to write a book. My layman's perspective is that it seems to follow from the belief that the public cannot understand the scientists' preferred decision, and that therefore the scientists must mislead the public "for their own good". The obvious example of course is the health authorities misleading the public on masks early on so that hospitals would be able to stockpile supplies, but I'd like to see even more places where the narrative is being twisted.

beezle 5y ago
An honest assesment acknowledges that current fusion research, like string theory and even HEP, has become an employment program. You can tell this is the case when 1) no efforts are made to change course once it is clear the current dogma is impractical, unprovable or lends increasingly marginal gains in knowledge at extreme cost; and 2) any who question the accepted view are shouted down and pushed aside. That is not to say there should be no money spent on researching fusion or the standard model (or beyond). Just that the current system does a poor job of allocating limited funds by putting most of the monies in one basket until well after other ideas/technologies should be given time of day and ample funding.

anonymousiam 5y ago

It's a valid point that ITER will not produce net power, but it's still a big step forward. Years ago I worked for a brilliant physicist who believed (usually correctly) that any factor less than an order of magnitude was just an "engineering problem".

Invictus0 5y ago
Did you read TFA? The author is not arguing that it's not worthwhile to fund fusion research; she's arguing against the misleading discourse surrounding it. "But it's still a step forward" is exactly the reason that science is misleading the public.
- anonymousiam 5y ago
  Yes. I RTFA and saw that. I was not disagreeing with her.
pfdietz 5y ago
Unfortunately for that viewpoint, the power density of a DT fusion reactor is at least an order of magnitude worse than commercial fission reactors. PWR reactor vessel = 20 MW/m^3, ITER = 0.05 MW/m^3, ARC = 0.5 MW/m^3.

2OEH8eoCRo0 5y ago

Commonwealth Fusion expects to start commercialization in 2025. They say it will put power onto the grid.

hamburglar 5y ago
What I’ve heard is that they will have a demonstration of “net energy” by 2025. This is still a long way from solving the engineering problem of putting energy on the grid. And if that “net energy” definitions is actually Q-plasma as this video claims, it’s a lot farther still.
- hobscoop 5y ago
  SPARC is aiming for Q_plasma of about 10 in 2025, but not to generate energy at all: it doesn't have any of the required 'blanket' system for breeding tritium. SPARC is a physics test, to make sure our theories of burning plasma are correct and to test the stability of these high field tokamaks. ITER is (among other things) supposed to be a physics test, but won't come until 2035. So SPARC's goal is to 'leapfrog' that by 10 years. You're right that there's a lot of work to be done between Q_plasma = 10 and generating energy. A lot of this work on the materials side, to engineer materials that can last for years in a fusion reactor environment.
dr_orpheus 5y ago
"This HTS magnet technology will next be used in SPARC, which is under construction in Devens, Massachusetts and on track to demonstrate net energy from fusion by 2025. SPARC will pave the way for the first commercially viable fusion power plant called ARC." [0] But this does not say that they are going to put power on the grid in 2025. They say net energy from fusion by 2025 which may just mean Q-plasma > 1, it does not say (which kind of proves the point of the article). They don't have any estimates of an on the grid fusion plant. https://cfs.energy/news-and-media/cfs-commercial-fusion-power-with-hts-magnet https://cfs.energy/news-and-media/cfs-commercial-fusion-powe...
- gene-h 5y ago

sb1752 5y ago

Good documentary on Iter's claims by investigative journalist, Steve Krivit. https://www.youtube.com/watch?v=xnikAFWDhNw https://www.youtube.com/watch?v=xnikAFWDhNw Shows that the public claims are not just an exaggeration but outright fraud for the purpose of getting more funding. It's one thing to say that the purpose is experimental research, it's another entirely to claim that it will produce net energy, which is not backed any evidence or even a reasonable scientific analysis. There's a long history of fraud in fusion research, it's really important the public is well educated on the history here.

deleted 5y ago
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mcwone 5y ago

Let not forget the total energy input it takes to construct the ITER project . We should not be wasting finite resources on this project.

m0zg 5y ago
The relatively minuscule resources "wasted" on this project could eventually solve the "climate crisis" in one fell swoop via delivering nearly inexhaustible sources of clean energy. So inexhaustible, in fact, that we could reduce CO2 by entirely engineering-driven (rather than ineffectual policy) means. And fusion would do so while also _increasing_ not _reducing_ everyone's standard of living. You could even use your gas guzzler still, by making gas from CO2 and water, and it'd be "carbon neutral" even if it belches a column of black smoke straight into the air. And this gas would be like 50 cents a gallon, too. I'd rather spend a trillion on fusion and get it done Manhattan project style than continue droning children in Afghanistan or funding $3.5T in pork barrel bullshit here at home. Just drown it in money completely until it's done. Put the very best people on it and let them have at it for real. We've done it before, several times, it worked. There's no reason why it wouldn't work this time. If there is any 21st century "Moon landing" type goal, this is it, and the United States is still best positioned to accomplish something of this magnitude. For how long that will be true I do not know, but it is true now.
- pfdietz 5y ago
  ITER has zero chance of solving the climate crisis. Anything derived from it will be far too large, expensive, and late.
  - m0zg 5y ago
    I'm not even talking about ITER here. Let them have their own nice European pork barrel boondoggle, though I'd point out that even if it fails miserably, it's still generating valuable science and technological capabilities that cannot be generated or sustained any other way, so it's not a "waste of resources". We're talking about these projects as if they'd offer marginal, rather than _radical_ improvements in our situation, which is simply not true. If this is done this will completely upend the world and make it a better place - there's no doubt in my mind on this whatsoever. This is the _only_ environmental thing I wouldn't mind paying more taxes for, but I'd argue we don't even need that - we just need to look a little bit ahead and allocate existing resources towards longer term, riskier things benefits from which we _know_ will absolutely dwarf the investment. The reason why this is not happening is because we have trillions of dollars flowing into other troughs from which everyone involved is used to feeding. Until we disrupt those arrangements somehow our only chance of solving this is private sector investment, but private sector can't sustain things of this magnitude over an extended period of time. Not unless Musk gets involved.

tuatoru 5y ago

This is what I like about scientists, they can change their minds based on the evidence. Well done, Sabine!

anonporridge 5y ago
To be fair though, I don't believe Sabine is involved in any nuclear fusion research, so changing her mind on this doesn't necessarily put her own funding at risk. Changing your mind is easy when your next meal doesn't depend on continuing to believe something. In fact, she might even stand to gain if funding gets diverted from fusion research towards other projects.
- willis936 5y ago
  If she was then she would have realized how ridiculous it is to directly compare Q performance between MCF and ICF machines, using Q as the metric to track progress, and not once uttering the words "triple product". This piece has about as much investigation as I put into the doneness of my toast.
  - kilotaras 5y ago
    Can you expand on that? I find the claim almost trivially true: we care about electricity production, so that should be the main goal we're tracking.
    - willis936 5y ago
      A high Q machine is expensive. It's by nature a nuclear facility, which adds a few zeroes to the cost. Nuclear fusion machines needs tritium fuel, which is made in exactly one breeder on the planet. In general a fusion machine just being nuclear doesn't add much scientific value. The plasma physics for making a better (cheaper) reactor has been pushed in smaller machines, as shown by better triple product values and empirical scaling laws. Triple product is a measure of how well the plasma is confined. That's the metric to focus on (when accounting for the fact that the science machines are small with scaling laws). In that regard, we have made excellent progress. A high Q machine (such as ITER) is valuable because it lets us study burning plasmas. It's an expensive pill to swallow but an essential step towards making a real reactor. Qtotal = 1 is a nothingburher. Qplasma = 1 is also a nothingburger, but at least going past that barrier grants new knowledge.

AlbertCory 5y ago

If you haven't read Sabine Hossenfelder, you should check out her other work. She is pretty acerbic about the politics of Big Physics.

willis936 5y ago
One should be able to tell from her bad faith implications without grasping the basics of the field.
- AlbertCory 5y ago
  what are her "bad faith implications" ?
  - willis936 5y ago
    That the physicists are deceiving the public. She's made a narrative around fusion progress without understanding fusion progress.

ufmace 5y ago

As I understand it, the bigger problem around fusion that we're still working towards fixing is being able to maintain an actively fusioning plasma. All of these Q measurements are around very short runs, sub-second I think. ITER seems to have a goal of 400-second runs, which sounds more like it. Once we have enough understanding of plasma physics and confining magnet behavior, it will hopefully be more straightforward to optimize the energy going into the plasma, and the energy going into the magnets and cooling system, etc to hopefully achieve a QTotal > 1. And maybe have enough heat being generated that it'll be necessary and reasonable to attach a boiler to it, hook it up to a steam turbine and generator, and make some electricity.

zardo 5y ago
W7-X was supposed to demonstrate a 30-minute run in 2021, but that's been pushed back a year.
- willis936 5y ago
  Mostly because of the you-know-what. W7-X is not a tokamak nor a nuclear machine. It's designed to run all day and no one on the planet doubts it. The upgrade to get it to 30 minute pulses is primarily to the heat dissipation subsystem. The ECRH subsystem of W7-X is eyewateringly beautiful.

mchusma 5y ago

I think the gap is not as far as the author purports. I've followed fusion research as a layperson for years, and clearly understand the point of these designs is to prove the most meaningful piece of the process of generating energy, not actually doing it, and that it would be a lot more work going from here to there. It think the summary on fusion is: - it's the most amazing energy source we have lined up in the mid term -ots almost certainly going to work - we are making meaningful but slower progress than we would like - it's dramatically underfunded

pfdietz 5y ago
My thinking on fusion is quite different. It's a technology that used to be considered the default future, but never made a lot of practical sense when examined closely, and now the justification for continuing to pursue it is becoming increasingly threadbare. In a decade or so this will become impossible for even fusion supporters to deny as the alternatives crash in cost.