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BlueSkyToday t1_j0oo3az wrote

With an input of about 2 MJ of laser energy they got about 3 MJ of energy out.

They required about 300 MJ of electrical energy to create those 2 MJ of laser energy.

IOW, the system is operating at about 1% efficiency.

Currently, there is no obvious path to improving the efficiency of the laser system to the point where this would be practical.

FWIW, I worked at LLNL. I worked for the guy who ran the NIF in the 90's and I worked with the guy who took over from him. They're each brilliant people and I have the greatest respect for them. But I don't see how this technology is ever going to be a practical means of producing power.

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bliceroquququq t1_j0rjty1 wrote

My dad was a plasma physicist working on ITER. My general sense of NIF among fusion researchers was that NIF was doing valuable experimental research and its work was important to continuing the advancement of understanding fusion reactions, but basically no one thought /thinks it would ever be a solid approach from a commercial/power production perspective.

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BlueSkyToday t1_j0ut9xn wrote

We may have overlapped.

I left the Lab in '89. I was working for Jeff Paisner in the AVLIS Process Physics group at that time and Ed Moses was Mr. Laser. Ed provided the laser power for both NIF and AVLIS.

Jeff went on to lead NIF and then went to Los Alamos. Ed replaced Jeff at NIF.

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probably_terran t1_j0qth10 wrote

Do people in the industry find the messaging around fusion ‘Q’ values as gross as I do (who is firmly in the Dunning–Kruger area of the knowledge curve)?

The media is gonna media going after clicks but even science people in interviews tend to gloss over or outright ignore the uncounted energy going in to the reaction and inefficiencies coming out (making Q total < 0.1 or worse). They make it sound like real world fusion is right around the corner. I can’t help but think they are doing it for the funding.

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BlueSkyToday t1_j0uu1yo wrote

There's interesting physics that you can learn from NIF and (aside from all that bomb design we didn, LLNL was ( is ?) mostly a research lab.

We agreed to stop blowing holes into the Nevada desert. I wouldn't be surprised if NIF is an important contributor to designing bombs. And unlike the Nevada Test Site, you can watch the reaction up close and in detail.

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ItsAConspiracy t1_j0z17je wrote

Qplasma > 1 has never been done before. It's a serious milestone that scientists have been pursuing for 70 years. It's just not a practical power plant yet. But it does mean the plasma gets more energy from fusion than from the laser, which is likely to help with experiments to improve the yield further.

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probably_terran t1_j0z3rev wrote

I didn’t mean to suggest it wasn’t a major milestone… but the first step of many and the goal of Qtotal > 1 is not particularly close. But a lot of the messaging ignores Qtotal completely and at least to me suggests ‘just a few more dollars and we’ll have clean free energy forever. trust me.’ I’d be fine with small scale projects but some (ITER) are billions. To me a proof of concept is worth more like millions.

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ItsAConspiracy t1_j0z830s wrote

True, but on the other hand a lot of articles have been overly pessimistic about NIF's distance from Qtotal. They point out how inefficient the lasers are, while ignoring that NIF's lasers are old, and equivalent modern lasers are about 40 times more efficient.

There's no getting around that fusion research is pretty expensive. The payoff could be huge though. At this point it might actually be private funding that puts us over the top. CFS for example has about a billion in private funding, to do the same thing as ITER in a much smaller package, using better superconductors.

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chasonreddit t1_j0rueyy wrote

> I can’t help but think they are doing it for the funding.

I'm sorry, I rarely use the phrase, but I've never found it more appropriate.

Ya Think?

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chasonreddit t1_j0rw7qj wrote

Thank you for this. I really tire of being the Debbie Downer on this topic. It's nice to have someone with some experience express concerns.

It is a great achievement make no doubt. In real terms it is a step toward practical fusion energy. But it is one step on a trip of 10,000 miles. I'm over 60. Fusion energy has been 20 to 30 years away my entire life. It's a hard nut to crack.

As to space travel, why don't we start building fission plant reaction rockets? Or even nuclear powered ionic drives? Sure, you'd have to launch them, but once up there, they could go anywhere. We could convert them to fusion if/when that becomes practical. Not that these things are easy, but they are doable with today's technology. Fusion power is simply not.

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BlueSkyToday t1_j0us0q1 wrote

People are kind of allergic to launching radioactive materials. You're one RUD away from dirty bombing yourself or your neighbors.

I can't see nuclear rockets happening anytime soon. It's hard enough to get small thermoelectric generators approved.

I'm not so sure that there's a conversion from fission to fusion. I don't see much commonality in the designs.

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chasonreddit t1_j0uvcp9 wrote

All very good points.

No way around launching radioactives. Until we can bootstrap enough to mine radioactives elsewhere.

The conversion bit is my own fantasy. But if you are using heated reaction mass, heat is heat. If you are using electricity well, does it matter the initial source? I'm think big transfer ships here, not optimized earth to orbit type things.

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BlueSkyToday t1_j0vdfzd wrote

Yup, heat-is-heat, but I think that there's about as much overlap between a laser fusion or a tokamak, and a fission plant as there is between a coal fired plant and a fission plant.

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chasonreddit t1_j0vebyu wrote

Well SI per lb of fuel is quite a bit higher for fission, but I understand what you are saying. Since we don't have a fusion reactor, it's hard to say what that might be.

Now I've always been fascinated by the concept of the Bussard ramjet, but that's a whole different animal and fictional as well.

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BlueSkyToday t1_j0wk7ye wrote

I suspect that the mass of the fuel is a very small portion of the mass of the engine.

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chasonreddit t1_j0wnkve wrote

Really depends on the distance and expected acceleration. You would be surprised. With Hohmann orbits, well those are designed to use minimal reaction mass. It's still a huge proportion. To really get around even the solar system you really want constant acceleration and ultimately 1 G acceleration. Even at high ejection velocities that's a lot of reaction mass.

I won't vouch for the math, but I remember reading that even with a 100% mass conversion drive (the ultimate) a ship would use approximately half of it's mass to make a round trip to nearer stars at 1G.

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ItsAConspiracy t1_j0z312i wrote

Fission fuel is barely radioactive before you start the reactor. It's just natural uranium, with a modestly higher percentage of U235.

It's the broken-apart atoms you get after fissioning uranium that are the really dangerous stuff. And to a lesser extent, heavier atoms that absorbed neutrons without splitting. So, just don't start the reactor until you're well away from Earth.

That would be way safer than what NASA has actually done multiple times, which is launch deep space missions powered by plutonium-238. That doesn't even need to be fissioned, its radioactivity is what powers the mission.

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BlueSkyToday t1_j106ge8 wrote

Yes, spent fuel rods are a lot more dangerous but the cost of mass to orbit is very high. Every plan that I've heard of calls minimizing the size of the reactor and the fuel load. So we're looking at highly enriched uranium or other possible designs. These are more of a problem than what we normally use in fission reactors.

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ItsAConspiracy t1_j10bji0 wrote

The half-life of U235 is 700 million years. The longer the half-life, the less radioactive something is, so even weapons-grade uranium at over 90% U235 is not particularly dangerous. You wouldn't want to eat it or inhale a large concentration of it, but you wouldn't want to do that with solid rocket fuel either.

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BlueSkyToday t1_j1p3ws0 wrote

In a world where people are deeply upset about the environmental health effects of fragments of shells made out depleted uranium, I don't think that scattering highly enriched uranium is going to fly.

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ItsAConspiracy t1_j1pzpeu wrote

And yet, plutonium-238 has flown multiple times, and that's way more radioactive.

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[deleted] t1_j0qjeuy wrote

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BlueSkyToday t1_j0uqwjb wrote

I was thinking laser fusion when I wrote that.

Unfortunately, I'm pretty dubious about fusion in general. We had a second fusion project at the Lab, MFE (Magnetic Fusion Energy). That was defunded in the 80's IIRC.

I don't understand projects like ITER. The machine is huge, and it uses a Beryllium jacket to increase the neutron flux because most of the energy in the fusion reaction is carried away by the neutron, but the neutrons get used up in the reaction, which means that they're not available to boil the water for the steam plant.

I've heard it said that ITER's jacket will use one year's worth of the World's production of beryllium. And beryllium is nasty to work with.

There are other groups working on alternative designs, some of them are very interesting but I don't know enough about them to make definitive comparisons.

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ItsAConspiracy t1_j0z4vx4 wrote

The kinetic energy doesn't disappear just because the neutron interacts with a nucleus. Any more than it disappears when a bullet hits a block of clay: the bullet mostly stops, but the clay moves and heats, because momentum is conserved. In the same way, ITERs breeding blanket is going to heat up plenty. Run water pipes through it and you're good.

The beryllium supply is a real issue though. CFS is working on a tokamak a tenth the size that should do the same thing as ITER, because it uses much better superconductors, but even that uses a lot of beryllium.

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ItsAConspiracy t1_j0z0t4d wrote

The lasers are very inefficient but that's because they date back to the 1990s. Equivalent modern lasers are over 20% efficient.

Also, they increased the laser output by 8% and got 230% more fusion energy.

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BlueSkyToday t1_j1028nc wrote

Still a very long way away from Engineering Breakeven.

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ItsAConspiracy t1_j10c903 wrote

Yes, about one order of magnitude.

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BlueSkyToday t1_j1p4udj wrote

Two orders of magnitude, and that's for a pulse reptation rate that you can measure with a calander.

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ItsAConspiracy t1_j1q0n0g wrote

One. They put in about 2 MJ and got back 3 MJ, and the laser input energy was about 400 MJ. With 20% efficient lasers, you only need 10MJ into the lasers to get 2MJ in the laser beam. So a factor of five for breakeven.

If you're generating electricity, you've also got a factor of 3 for the heat cycle loss, so a 15X gain for engineering breakeven.

The pulse repetition rate is also due to the obsolete lasers. Modern petawatt lasers can do better than one hertz and are still improving (see my first link above).

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ModsAreBought t1_j0zxp12 wrote

They started a self perpetuating reaction using 200 MJ. That's a one off expense. The next gain of 1 MJ continues after that. You can recoup the startup cost over time.

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BlueSkyToday t1_j0zyzbq wrote

It's not self perpetuating. You need to thwack each pellet with a laser pulse.

The laser pulse creates an X-ray cascade from the jacket of the pellet. The X-ray pressure is what compresses the fuel.

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