7 ms·

Can someone explain to me like I am 5 years old what else is needed to make fusion practical?

msdrigg 5y ago
Edited to add source Im not an expert but someone pointed out yesterday [0] that this technology is a bit further from practical than implied by the article. This milestone of ‘ignition’ is declared because the laser energy making it into the fusion fuel is less than the energy produced by the fusion fuel. But this is ignoring the fact that there is significant (85% if I remember correctly?) loss of energy as the laser travels through the housing around the fuel. And even more importantly, the laser itself is very inefficient and loses something like 99% of the energy that it pulls from wall power. So even in lab conditions, we need to produce several times more energy to even call it ‘ignition’. And this is not mentioning the many and difficult issues with scaling from lab scar to real-world power plant scale. [0] https://news.ycombinator.com/item?id=28213763 https://news.ycombinator.com/item?id=28213763
willis936 5y ago
A carbon tax. The rest is gravy. Also, NIF is not a fusion power research project. Articles that discuss both NIF and fusion power research confuse the public.
hannob 5y ago
I can recommend a great article answering that, however unfortunately it's in German [1]. But the gist is that there are two major unsolved challenges. One is finding a material stable enough to let the reactor run for longer times (all experiments like ITER only plan to run the reaction for very short times, which is okay for research, but not useful for real energy). The other is finding a way to produce enough tritium for the reaction. It is expected that ITER alone will consume all the tritium that is available and that is currently only produced in some special kind of nuclear reactor. The idea is that eventually fusion reactors will create this tritium themselve, but noone has figured out how to practically do that. [1] https://taz.de/Energie-durch-Kernfusion/!5707537/ https://taz.de/Energie-durch-Kernfusion/!5707537/
- willis936 5y ago
  Tokamaks are inherently pulsed machines. No material will change this. Stellarators are very similar to tokamaks but do not use a central solenoid/transformer to induce the poloidal twist: they use the geometry of flux surface/coils/vessel. Stellarators are steady state. Tritium breeding blankets have been the answer to question 2 for longer than I've been alive. The real engineering challenges lie in divertor physics and strike point materials.
  - tomsto 5y ago
    This sounds interesting. You sound like you work in nuclear physics. Please can you explain, or link to an explanation of, divertor (sic?) and strike point materials?
jjk166 5y ago
A lot. This milestone of ignition is an important one - the energy released by the initial fusion was of sufficient quantity and sufficiently contained that it could in turn cause more fusion, which in turn could cause more fusion. It is analogous to holding a lighter to a piece of wood and getting the wood to continue burning after you take the lighter away. Hence the term ignition. That said, while our fuel was alight for a little bit, it still extinguished itself pretty quickly. The energy released by the burning fuel was more than what the fuel recieved, but it was still only a fraction of the power output by the lasers (the lighter), which in turn is only a tiny fraction of the power it takes to make those lasers fire. This reactor can do one of these shots every couple of months. A reactor of this type producing useful amounts of power would need to produce about 41,000 times as much energy per shot, and fire shots at about a 14,000 times higher rate to generate 300 MW of continuous thermal power, which could be converted to about 100 MW of electrical power. To go further and make it practical, you need to do all that while also decreasing the price tag by about 90% and solving various technical hurdles such as fuel production and reactor maintenance. On a scale from 1 to 10 where 1 is "might be physically possible" and 10 is "we are ready to build a bunch of these", the technology is approximately a 3.
dredmorbius 5y ago
A solar mass.
- jbotz 5y ago
  This. We already have a fusion reactor... it achieved ignition some 5 billion years ago with enough fuel to sustain itself for about 10 billion years (5 down, 5 remaining). It's conveniently located at a safe distance suspended in empty space at the center of our solar system. All we have to do is harvest the energy it's producing, and we have the tech to do that, including a road-map for growing civilization by many orders of magnitude using that energy (up to a full Dyson sphere). As for the notion that somehow you can harvest useful energy from a fusion reaction using anything less than the mass of a star... well, at the very best it isn't likely to have a very good EROEI (energy return on energy invested) because no matter how much progress we make it will always be expensive to ignite and then contain a mini-star. And it's quite possible, even likely, that the EROEI will always remain negative.

Edited to add source Im not an expert but someone pointed out yesterday [0] that this technology is a bit further from practical than implied by the article. This milestone of ‘ignition’ is declared because the laser energy making it into the fusion fuel is less than the energy produced by the fusion fuel. But this is ignoring the fact that there is significant (85% if I remember correctly?) loss of energy as the laser travels through the housing around the fuel. And even more importantly, the laser itself is very inefficient and loses something like 99% of the energy that it pulls from wall power. So even in lab conditions, we need to produce several times more energy to even call it ‘ignition’. And this is not mentioning the many and difficult issues with scaling from lab scar to real-world power plant scale. [0] https://news.ycombinator.com/item?id=28213763 https://news.ycombinator.com/item?id=28213763

willis936 5y ago

A carbon tax. The rest is gravy. Also, NIF is not a fusion power research project. Articles that discuss both NIF and fusion power research confuse the public.

hannob 5y ago

I can recommend a great article answering that, however unfortunately it's in German [1]. But the gist is that there are two major unsolved challenges. One is finding a material stable enough to let the reactor run for longer times (all experiments like ITER only plan to run the reaction for very short times, which is okay for research, but not useful for real energy). The other is finding a way to produce enough tritium for the reaction. It is expected that ITER alone will consume all the tritium that is available and that is currently only produced in some special kind of nuclear reactor. The idea is that eventually fusion reactors will create this tritium themselve, but noone has figured out how to practically do that. [1] https://taz.de/Energie-durch-Kernfusion/!5707537/ https://taz.de/Energie-durch-Kernfusion/!5707537/

willis936 5y ago
Tokamaks are inherently pulsed machines. No material will change this. Stellarators are very similar to tokamaks but do not use a central solenoid/transformer to induce the poloidal twist: they use the geometry of flux surface/coils/vessel. Stellarators are steady state. Tritium breeding blankets have been the answer to question 2 for longer than I've been alive. The real engineering challenges lie in divertor physics and strike point materials.
- tomsto 5y ago
  This sounds interesting. You sound like you work in nuclear physics. Please can you explain, or link to an explanation of, divertor (sic?) and strike point materials?

jjk166 5y ago

A lot. This milestone of ignition is an important one - the energy released by the initial fusion was of sufficient quantity and sufficiently contained that it could in turn cause more fusion, which in turn could cause more fusion. It is analogous to holding a lighter to a piece of wood and getting the wood to continue burning after you take the lighter away. Hence the term ignition. That said, while our fuel was alight for a little bit, it still extinguished itself pretty quickly. The energy released by the burning fuel was more than what the fuel recieved, but it was still only a fraction of the power output by the lasers (the lighter), which in turn is only a tiny fraction of the power it takes to make those lasers fire. This reactor can do one of these shots every couple of months. A reactor of this type producing useful amounts of power would need to produce about 41,000 times as much energy per shot, and fire shots at about a 14,000 times higher rate to generate 300 MW of continuous thermal power, which could be converted to about 100 MW of electrical power. To go further and make it practical, you need to do all that while also decreasing the price tag by about 90% and solving various technical hurdles such as fuel production and reactor maintenance. On a scale from 1 to 10 where 1 is "might be physically possible" and 10 is "we are ready to build a bunch of these", the technology is approximately a 3.

dredmorbius 5y ago

A solar mass.

jbotz 5y ago
This. We already have a fusion reactor... it achieved ignition some 5 billion years ago with enough fuel to sustain itself for about 10 billion years (5 down, 5 remaining). It's conveniently located at a safe distance suspended in empty space at the center of our solar system. All we have to do is harvest the energy it's producing, and we have the tech to do that, including a road-map for growing civilization by many orders of magnitude using that energy (up to a full Dyson sphere). As for the notion that somehow you can harvest useful energy from a fusion reaction using anything less than the mass of a star... well, at the very best it isn't likely to have a very good EROEI (energy return on energy invested) because no matter how much progress we make it will always be expensive to ignite and then contain a mini-star. And it's quite possible, even likely, that the EROEI will always remain negative.