First of all, the reactions are not self-sustaining or anything, they require constant intervention to be carried out.

Most unavoidably though, the global energy use last year was about 10^20 Joules. This is approximately equivalent to 1000kg or 1 tonne, obviously there is an efficiency in there somewhere but that means that you need to turn 1 tonne of matter into energy per year to fuel the entire world. The Earth weighs 10^21 tonnes and although we can only fuse specific elements (mainly hydrogen) there is still such an abundance of that in the sea alone that we will not run out for millions of years even if our energy consumption went up a thousand fold.

Yes that article is completely wrong.

It even clarifies in the first section:

"Ignition should not be confused with breakeven, a similar concept that compares the total energy being given off to the energy being used to heat the fuel."

edit:

it also changes its definition multiple times throughout the article, that article is horrible. The definitions they give means NIF either achieved it on its first ever experiment or it is impossible for NIF to achieve it (id personally say the latter is true) it also claims it is a necessary pre-req for power - not true remotely. It also precludes all tokamaks from ever achieving it due to external heating being used for plasma control and h-mode access even if internal heating is 10 times higher (or 1000 or a billion).

I agree with the sentiment here but I would point out that the first ever successful controlled fusion ignition (so we exclude the obvious fusion weapons) was in 1958 with a theta pinch machine. Fusion is achieved dozens of times a day at a large number of reactors and nif has routinely ignited fusion since it was commissioned. Nif achieved a milestone with this experiment but not the first ever fusion ignition.

Sorry the scrape off layer is a tokamak concept. I am not sure how ICF machines are supposed to handle waste.

The best ones are only matter of tens of seconds. ITER is meant to be 1000s but the ultimate goal is continuous operation. Nif and other icf machines are necessarily pulsed (because they are explosions).

Maybe. Fusion is sometimes seen as a bit of a joke already because while experts are very realistic amongst each other at some point in the dissemination of results the headlines become inaccurate and exaggeratory.

During the shot there is a constant removal of helium from the outer edge of the machine. A region called the scrape off layer. which is a lot cooler than the rest. The fuel is replaced with pellets of ice fired into the machine.

It is essential that unburnt fuel is recovered and used in another experiment. Well it is essential that tritium is recovered because it's expensive.

Destroyed in the explosion!

So I assume you are talking about magnetic devices: the core temperature is a lot higher than the outer edges but the answer is, nothing. No material can withstand those temperatures plus if you did let your plasma touch an outer wall it would cool down. So that's why they contain the plasma with magnets, this holds it away from the walls (which are either carbon in old machines or beryllium/tungsten in new machines) and stops it from destroying the vacuum vessel.

Even then though when there are large instabilities or runaway electron beams the walls get damaged sometimes.

I think that I did not mean that there is not large efficiency gains to be made just that they can not eliminate their biggest inefficiency, unlike MCF which just removes the iron core magnets. I also disagree that this fundamentally changes the point I made. The most efficient diode pumped lasers are about 10% efficient (the primary beam on NIF when still IR is about 1% efficient.) and there is speculation that this could be 17%-18% in the medium term. So there is maybe a 20x improvement available.

The swap from iron core magnets to superconducting magnets completely eliminates that energy cost and is current technology, if JET had superconducting magnets in 1996 it would have reduced its energy usage by a factor of 40. This reduction is obviously present in all next gen tokamak designs.

The majority of the improvements therefore still need to come from target yield where I believe they need to hit several hundred MJ if not higher, so a further 2-2.5 orders of magnitude needed there. (NIF can handle up to something like 50 I think in terms of the chamber max, not the fuel max).

In comparison JET is about 1 order of magnitude less than ITER and ITER is larger in terms of power than power plants will be.

I would also be remiss if I didn't take the opportunity to point ouit that 6 orders of magnitude in repeat rate are needed.

Microseconds.

Some of them are blowing hot air for investment reasons, some of them are just flat out scams. The remainder are simply doing very simple jobs and acting like they are reinventing the universe.

I've seen some propositions that rely on things like magnetic bottles for confinement rather than tokamak designs and they just will not ever work, we moved on from those designs 60 years ago for good reason.

More players in the game means more progress too so I'm not bothered by their presence - as long as it doesn't reduce funding for the mainstream experiments by virtue of having to necessarily criticise them in order to justify their own work.

That is the design that they are working towards. Well NIF isn't really about a pathway to fusion power but if you are following a NIF-like design for power than it needs to be pulsed. It needs to be pulsed a couple of times a second before designs start to make sense (nif is about once a day).

Modern fission designs can also not melt down (search for Gen IV or gen V reactor designs), they are completely passively controlled and cooled.

In addition magnetic fusion devices can not melt down either, they might damage the machine if you turned them off (also JET makes a horrible bang if it is turned off early) but there is no risk to anyone, reaction stops the instant you turn it off.

Absolutely correct. Tonnes of high density matter stuff is classified, if you do work on this in general with laser plasmas the government is gonna come and steal your work (has happened to acquaintances).

I think though the limiting factor in making a passable h-bomb is the fission warhead though, not the fusion stage. The US and other nuclear powers care about this stuff to make efficient and clean weapons rather than to just make weapons (they made them in the 50s without any lasers or plasmas).

I can try to answer these follow ups:

1. For sure there is efficiency to be gained, 20% is definitely achievable but not for a long time (maybe only when using a non frequency doubled laser), currently the most efficient diode pumped lasers are about 10% efficient. At 20% this means a 20x improvement (if you can deliver the 4MJ rather than 2MJ to target. It is hard to imagine much more improvements over that, but there is a huge ceiling for improvements in the fusion yield. They need both to get the 5 or so orders of magnitude they need between both. I would point out though that the demands on the laser are different for the different purposes, technology translates but not without adaptation.

2. I 100% agree that one of the few (maybe only significant?) advantages of ICF is the target chamber being very simple. They actually also benefit from a smaller neutron blanket being necessary but it isn't all positives, the number of laser beam paths needed to evenly heat the holhraum makes fitting the blanket around the outside comparatively tricky.

3. I don't believe this is either true or an advantage. NIF uses less tritium because it does tiny shots once a day. Jet pulses every 20-30 minutes with much higher amounts of tritium in each shot because it generates far more energy (50-100x more roughly) so requires far more fuel on site. Fundamentally I disagree there is a proliferation problem, tritium is not the limiting step in making a hydrogen bomb (the fission warhead is far harder) nor is it essential, DD is sufficient. Lastly, we don't like having it around because it is hard to handle, and extremely radioactive, I don't think it is in particular due to proliferation fears.

4. So NIF is a weapons lab but it is somewhat supported by the fusion-for-power cause too. It does what it is designed to do very well (test equation of state of high density matter, test x-ray ablation of hydrogen targets, test compression and fusion of hydrogen targets). It does fusion for power reasonably badly. Without going off on paragraphs of text, MCF problems are numerous but they are mostly understood, we know we need different divertor designs and what they should be, we know we need better ELM control, we know we need to conquer tritium breeding and material science under neutron bombardment. ICF has similar problems and then 100 other ones - in the context of fusion for power. There is no sensible plan to get a 2-10Hz repeat rate on it (versus the 0.000001Hz of NIF), there is no sensible plan to get fabrication costs down by a factor of 1000. And on top of all of that MCF machines built in the 90's are about 1-1.5 order of magnitude away from our goal in terms of raw power output. (JET at 30MW versus ITER at 500MW with the same heating). ICF is 3 or 4 away (Again alongside the 6 orders in repeat rate). The disclaimer here is that ICF is extremely new science and MCF is established so there is plenty if time for ICF to mature. I'll leave it with saying that the steady state nature of a tokamak (maybe 1000s flat top burns not being out of the realms of possibility for ITER) just makes so much more sense as a power plant than pulsed explosions.

5. Funding both of them makes 100% sense to me, I have no issues with ICF or with laser plasma physics in general and as I've said all over the place, NIF is an incredible feat of plasma physics and engineering. I doubt a commercial reactor will ever use both in my lifetime (in fact I doubt one will use ICF in my lifetime) but I am 100% certain there will be a tokamak power plant.

> fusion power is more of a political or engineering question than it is a scientific and physics question?

I'd say not yet.

There are still fundamental physics questions that remain in terms of optimising the plasma, you have 100's of knobs to tweak when designing and operating a machine and we aren't sure exactly what combinations are optimal - though we are getting better, modern machines achieve a huge milestone, called H-mode access, almost instantaneously when this used to be something that took years of tweaking parameters.

Engineering challenges will take over significantly in a post ITER world, when we are trying to design a demonstration power plant.

Once that has been successful it will become a political and economic issue, when is it worthwhile to invest, where should we build them, what does the energy landscape of our country look like 50 years down the line.

I asked the director of JET one time "if you had a blank cheque, similar circumstance to the manhattan project, when would a fusion power plant be ready".

His answer was that we could just build a massive machine. There are a lot of problems in MCF surrounding stability and confinement time that are so much easier in big machines but big machines are extremely costly. If you had unlimited money then you could build a stupidly expensive machine and eliminate some of the physics and engineering challenges (you do introduce some others, mostly in the diverter region).

As for ITER in particular, it is so close to being built that budget isn't really the issue. Sourcing components and waiting for them to be built is just time consuming, I suspect you could shave some time by expediting some things and increasing construction staff etc.. If you had triple the budget from day 1 then you would probably have a bigger and more complex and powerful machine, you would definitely be able to shove it through some of the commissioning and design and site location phases but I doubt construction is that much faster.

85 to 90% is my understanding. One of the areas where there isn't much to be gained surprisingly!

The design goals for those commercial purposes are completely worlds apart. There are already much better suited lasers to the jobs you list than NIF which would be completely useless in any of those applications. Completely useless Even if it wasn't useless (which again it would be) it costs billions which isn't exactly gonna come down to a level that makes sense as a commercial product.

I can't see ICF being an energy source in even the long term future (would love to be wrong). Tokamaks maybe by 2050-2060 for the first significant power producing power plants and how widespread they are is as much an economics as physics question.

Unfortunately, similar to its magnetic brothers, this machine produces completely insignificant quantities of helium (Fractions of a gram).

Absolutely, NIF will continue to find efficiencies and new strategies and smash this record. There have also been an absurd number of lessons learned from NIF and as such the experiments carried out today have compromises that have adapted the initial design due to these lessons. A next generation machine could incorporate these lessons from the start and make no such compromises.

So there is so much more room for this result to grow but the level they need to improve to reach anything that can be called power generation is extreme, at least 3 orders of magnitude more in power generation and at least 5 orders of magnitude in repeat rate (MCF who I will sound like I am shilling for is probably only looking for 1-2 orders of magnitude improvement in confinement time and energy output).

> What's the proliferation risk of pulsed fusion technology?

I mean the flippant answer is that you don't need lasers to make a bomb, it is much easier to compress your fuel with a fission explosion than with a laser. You also might be envisioning some sci-fi scenario where you lob your pellet at them then lase it to explode but that simply isnt possible, the symmetry required in the compression is almost absolute and the experiment requires a vacuum.

>Could you build a pure fusion bomb, a thermonuclear weapon without any uranium needed at all?

Yes, NIF though has a an entire building that generates the laser pulse and took years to build and it could only blow itself up, not easy to drop it on anyone.

As for question 2.

>were to use an NIF-type facility to breed fissile materials from non-fissile ones?

I believe there are just better ways to do this, and I mean much much much better ways. There are other neutron sources which are cheaper, easier and produce better neutrons than NIF and the actual fusion explosion doesn't help except as a neutron source. The most obvious neutron source is a fission reactor but there are others, any country could build a breeder reactor if they wanted to (though they might face consequences if they were seen to be using it for weapons tech).

A very nice thing to say, thanks. I am glad it was informative.

So efficiencies gains are always possible but probably not unlimited. There are also fundamental science problems for both fusion regimes that need to be solved (even though I will claim ICF has far more of those problems).

> A solution to our energy/climate crisis for good?

I have a bog standard answer to this question: Just because there is unlimited fuel doesn't make it cheap. Fusion reactors will be, for the foreseeable future, extremely expensive. This means the energy they produce will be very expensive.

However, they will get cheaper as we learn to make them better and as energy prices rise there will always be a tipping point where they make economic sense. More importantly though is your mention of climate. While there are obviously some co2 emissions associated with fusion (due to the plant needing built and operated and the fuel collected etc.) the amount is trivial so the environmental benefit of fusion is huge. Traditional Nuclear power also shares many of these benefits too but produces larger quantities of waste (though fusion still causes nuclear waste due to neutron activation of materials) and requires larger quantities of fuel.