It’s strange that controlled fusion is an energy sink, but whatever black magic is happening inside an H-bomb manages to unlock so much “free” energy.
The history of fusion research for the past 70 years is trying to figure out a cost-effective way to trigger enough fusion to make net energy without a nuke. So far, we've got bupkis. (The magnetic containment approaches using high-temperature superconductors seem promising, but we won't know they actually work until we've built them.)
E=mc^2. The proportion of the original mass converted to energy in fusion is higher than it is for fission.
The trouble with fusion is that you need really high temperatures and pressures to sustain it. You can easily sustain a fission reaction at a few hundred degrees C, or even lower than that if you wanted to (but the general goal is to boil water to run a steam turbine so >100°C is what you want).
Fusion requires millions of degrees, which would vaporize most things you might want to use as a container, so instead they use strong magnetic fields and then you spend a lot of energy maintaining the magnetic field. A bomb doesn't care about that because sustained operation isn't required and vaporizing everything in the vicinity is kind of the idea.
Moreover, efficiency isn't really the issue. The efficiency of fission is already absurd. Fission of a given mass of uranium generates the same amount of energy as burning 2.7 million times that amount coal -- by mass, it's even more by volume.
The main advantages of fusion are that hydrogen is a lot more common than uranium (though uranium is still pretty available) and that the byproduct of fusion is helium (a non-radioactive noble gas with general usefulness), whereas some of the fission byproducts are variously radioactive or have limited known commercial applications.
So, fission bombs are the black magic.
It’s a much more efficient version of inertial confinement fusion like at the NIF.
Thermonuclear bombs literally create lots of heat, and don’t tend to drive anything that produces work. It’s the opposite of efficient.
Just like lighting gasoline on fire and claiming that that’s more efficient than a combustion energy…
Further fission here requires a fission first stage which represents a huge additional energy input.
I trust the argument. You can look into it yourself. Long story short, it is massively energy positive compared to controlled fusion.
ITER is supposed to be a 10-20x return on energy provided (10x being a basically guaranteed minimum) which means it may or may not be better depending on the specific bomb design, but it’s not massively better.
People talk about fusion as useless and slow but the current record holder in steady state was first turned on in 1983 and hit 0.67 in 1997. It’s not a failure of the underlying technology, it’s a near total lack of investment that’s stalled progress. ITER was started under the first Bush presidency and scaled back to a minimum design. It could have easily been built 20+ years ago if it was an actual priority.
https://www.iter.org/fusion-energy/what-will-iter-do
Really the actual science bits are focused on the breeding blanket, remote operation, material science, etc hitting a high Q on DT doesn’t matter with the world’s supply of tritium so minimal. DEMO might be targeting Q=100, but that’s only useful if the tritium supply is sufficient and the timeline ends up way faster than starting in 1978 to only see a ~2033 first plasma.
That is a bad thing to do. We diversified bets, and we end up finding a couple of pretty good energy sources, plus making some of the existing ones cleaner and safer.
Had we put all our money in fusion, today we might be drowning in cheap clean energy... or still living in a dirty coal-fuel environment, with a few old and dangerous fision reactors for lack of investment in development. A very risky bet.
Spend 1 billion/year (in today’s money) from 1987 and by 2006 you’re well past ITER’s projected cost back then there was little advantage to waiting. JET’s first plasma was 1983 so that’s another 10 years for design and 12 years for construction.
By comparison the US was spending ~12 Billion / year in energy R&D in 1978 (2026) dollars. That fell over time, but it’s not like total energy R&D spending couldn’t have increased vs historic levels. https://www.congress.gov/crs-product/RS22858
We don't know this. There are a number of investments that fail and the investors need to let go or you get into the phallacy of sunken costs. E.g. wave energy was a failure, thermo-solar under delivered, algae based fuels never scaled up, and ethanol fuels from waste proved very difficult to engineer, syngas was a ecological nightmare... All of them received significant investment, and they were abandoned, pivoted or relegated to niche applications. I personally would throw fusion in that same group of failed investments.
Luckily for us, solar PV (paired with batteries) is a huge win that justifies all the above failures: for decades it was a dream for the 25th century, but some people make it true in the 21st.
Not every spending/investment ends up in success! Fusion is one hurdle after another, yet it advocates still believe that is just a throw-more-money-at-it problem. I am not so convinced. Of all the failed (for now) energy sources, fusion is the biggest money sink. France spent 25 billion, plus 7 billion in private funds. It is not like they are working with peanuts, at those quantities you have to show some serious results, maybe facing scaling problems rather than basic development problems (e.g. ethanol failed at scaling, when it already proved viable on smaller scale. Fusion is not even in "we have this toy reactor that works we are fighting to scale" phase).
Except we do know this because people built similar systems at similar scales and temperatures before.
> All of them received significant investment
Not compared to Nuclear, Fossil Fuel, or PV R&D + subsidies. For scale in the US alone “From FY 2016 to FY 2022, federal subsidies for renewable energy totaled $183.3 billion” That’s more than 1 ITER per year, and splitting that budget across multiple countries and 2 decades is a very different proposition. Especially as there was ITER funding in this time period so the delta is less than the full cost of the project.
Further look at the timeline, I’m suggesting the project should have finished long before PV became cheap.
Did we? Where are those fusion plants installed?
> Not compared to Nuclear, Fossil Fuel, or PV R&D + subsidies
You are probably referring to this document: https://www.eia.gov/analysis/requests/subsidy/pdf/subsidy.pd... . A huge share of the $183.3 billion are tax expenditures, which is to say they reduce taxes on activities related with energy (e.g. nuclear decommissioning is tax free). That is not the same as throwing money at those technologies R&D, but it counts as subsides because they can operate more cheaply. Only $11 billion of the $183.3 is true expending. But they mix R&D with other direct expending, like guaranteed loans. In Figure 11 we can see that R&D for all renewable energies is less than $300 million.
Fusion energy don't want tax expenditures, they want cash and lots of it.
Oxfordshire etc but most of the cost is stuff you’d see at any nuclear power plant.
> Only $11 billion of the $183.3 is true expending
That’s not how money works, there’s zero difference between a tax break and handing out money because money is fungible. The IRS will write you a check on a “tax” break.
Thermonuclear assemblies don't have a chain reaction, so they can burn most of their fuel, once they get hot enough.
Also, you interestingly reminded me that fusion is unlike fission, the latter being a chain or cascading reaction (the self-sustaining kind), while former isn't (or is it? :M.Stevens face:)
I'll add another observation: the secondary in a thermonuclear bomb is a lot like the target in inertial confinement fusion, only much larger. The expansion time of these systems is proportional to their radius, so if (say) the bomb has a million times the fuel, it takes 100 times longer to expand. So for a given density and temperature of fuel, there is 100x as much time for the fusion reactions to occur. In a real sense, thermonuclear bombs become easier to build as they get bigger.