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Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

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Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#231

Post by mikeyouse »

Systemic33 wrote: post #50
rob74 wrote: post #43

Still unconvinced why this is such a major breakthrough - it may be the first net-positive controlled fusion, but the distinction between controlled and uncontrolled fusion is a bit academic in this case. In uncontrolled fusion ( https://en.wikipedia.org/wiki/Thermonuclear_weapon ), you are using a nuclear fission primary stage to generate enough energy to start the fusion reaction in the secondary stage. In the NIF,…

With regards to NIF being a military facility, I'd very much think that energy production (cheap, safe, limitless?) is very much a military needs as much as a civilian need. Even if said energy goes further to power laser weapons or other exotic power hungry systems; energy is energy, and something has to produce it.

NIF being a "military facility" has less to do with laser weapons or power-hungry systems than their type of research indirect drive laser-fusion, being the exact mechanism that takes place in multiple-stage nuclear weapons. The lasers at NIF first generate x-rays, which are then focused on the target to energize the pellet and create fusion.

If you look at the "shot history" of NIF -- the vast majority of their facility's energy is spent on actual DOD weapons research, not fusion power research that would be incidentally beneficial to the DOD:

https://lasers.llnl.gov/for-users/nif-target-shot-metrics

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#232

Post by russdill »

felipellrocha wrote: post #203
throwawaymaths wrote: post #158

Earlier quoted context omitted.

It's not even close to net positive. It's more energy out than the lasers put in. But the lasers take in WAAAAY more than they put in.

What are you talking about? They put in 2MJs of energy in, and got back 3.5MJs out?

They lasers are about 1% efficient. The actual energy required is hundreds of MJ.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#233

Post by zardo »

donquixote25 wrote: post #205
throwawaymaths wrote: post #162

Earlier quoted context omitted.

No it's not a breakthrough. It is only net positive because the NIF has an exquisitely stupid and convenient place where they are defining "energy in" which let's them cheat how good it looks. If you could take other types of fusion and draw a clever line around where you start tallying energy in, then they would have had "breakthroughs" long ago.

The definition of Q that is being used was established by the National Academy of Sciences not NIF. NIF previously tied to use the hot spot energy instead of target energy in 2013, which they were criticized for, and rightfully so. But this definition of Q is analogous to the definition of Q used by MCF.

Correct me if I'm wrong, but I thought the Q typically used for MCF does not count the energy in neutrons, only the alpha particle energy.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#234

Post by smt88 »

idiotsecant wrote: post #225
jliptzin wrote: post #163

Earlier quoted context omitted.

Didn’t we already know it’s just an engineering problem by virtue of the sun existing?

Boy, the HN pedantry is potent this morning. The fact that black holes exist does not mean that we can spin one up to harvest it's hawking radiation for power. It's not just an engineering problem. That's not what that phrase means.

Your point is well-taken, but please be less of a jerk about it.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#235

Post by russdill »

subradios wrote: post #23
LatteLazy wrote: post #8

The title doesn't match the contents. There is no actual justification of why this is a breakthrough. IMHO it's a milestone, not a breakthrough. This is because it is only a marginal improvement on previous results and it is very unlikely to significantly change the state of either the science or industrial products without further work.

This specific marker is a breakthrough. We did not know until three weeks ago if laser ignited fusion reactions could be created that released more energy than was transmitted into the fuel. Now we know it is possible, it has been done. The next question is, can we create enough industrial efficiency to create a working motor generator set. A hard problem to be sure, but proving that it is a problem that we have is i…

I'm confused why it matters. If I heat something with 2J of energy and it released 1J of energy, it's like the matter has been heated with 3J of energy. If I can extract heat energy with 80% efficiency, I can extract 2.4J, more energy than was put in.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#236

Post by ipdashc »

donquixote25 wrote: post #226
ipdashc wrote: post #222

Earlier quoted context omitted.

I realize this may be too complicated to explain in one comment, but as a layperson... can anyone summarize what they actually did to achieve this sudden gain in power? Like, what have they been doing for those 11 years? Upgrading the lasers, improving the optics, refining the design of the hohlraum, changing up the fuel? I know this is the cutting edge of physics and all, and maybe there's some DoE secrecy involved,…

I don't think anyone specifically knows. If you ask the physics, they will point to changes (like pulse shape or component sizes) they made due to their increased understanding of the physics. If you ask the target design people, they will point to decrease fill-tube size and number of defects in the capsule. If you ask the facility, they will say their ability increase both power and control power delivery. Likely,…

Thank you!

What does "component sizes" and "fill-tube size" refer to, BTW? And the quality of a shot thing you mention in the last line? Sorry for all the questions, just curious

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#237

Post by mikeyouse »

ipdashc wrote: post #222
donquixote25 wrote: post #209

Earlier quoted context omitted.

I mean NIF has spent a majority of its life (11 years) seeing yields below 200 kj. Only in 2021 did it jump above 1 mj and in 2022 above 3 mj. If your definition of breakthrough is rapid improvement, I think this demonstrates it: See below for previous yields of NIF shots. https://en.wikipedia.org/wiki/National_Ignition_Facility#/me...

I realize this may be too complicated to explain in one comment, but as a layperson... can anyone summarize what they actually did to achieve this sudden gain in power? Like, what have they been doing for those 11 years? Upgrading the lasers, improving the optics, refining the design of the hohlraum, changing up the fuel? I know this is the cutting edge of physics and all, and maybe there's some DoE secrecy involved,…

This powerpoint from last February has a good rundown in the context of the 1.35GJ shot from August 2021:

https://www.orau.gov/support_files/2022ssap/presentations/Da...

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#238

Post by floxy »

chasd00 wrote: post #197
sudhirj wrote: post #65

It’s practical proof that in a single pulse we can get more energy out than we put in. We do spend a shit ton of energy setting up the pulse, and we haven’t figure out how to get that energy out and make electrons move, but it’s been proven possible. The “breakthrough” is the proof that it’s possible. Everything else is now optimisation and engineering, and needs mostly time, sweat and money.

I wonder how the composition of the pellet was optimized. I'm sure the pellet was setup to make ignition as likely as possible. Now that they've accomplished that i wonder if parameters can be changed to up the efficiency of the reaction for energy output? Granted, optimizing for likeliness of ignition may well be the same as optimizing for energy output. Can they just up the mass of the pellet for a longer fusion re…

>Can a multi-stage pellet be formulated? Ignition of an outer pellet provides some energy to get a more powerful inner pellet ignited.

My understanding is that that is the whole point of the announcement. The initial laser induced fusion caused further fusion of the interior. That's why the gain is greater than one. And that's why there is excitement, the possibility is there to scale things up using larger/more massive pellets. To me, that's the real announcement, the laser initiated fusion created additional fusion. The whole break-even energy seems more like a red-herring. Also, with inertial confinement fusion you have the possibility of doing the harder fusions, (like aneutronic fusion), that magnetic confinement fusion would have a much harder time with.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#239

Post by corille »

mikeyouse wrote: post #213
corille wrote: post #200

Earlier quoted context omitted.

There are different kinds of lasers. Last time I checked in 2018, Nd:glass lasers were the only choice for producing short, ultra-high power laser pulses with regular beam profile. Beam profile is very important for tight focusing. They may be 80's technology but these were produced in 2005. Efficient fiber optic lasers were already available but they are not suitable for the task. https://lasers.llnl.gov/about/how-n…

So the NIF spec'ed out a replacement using a diode-pumped Yb:SFAP laser that they estimated to be 10% efficient in ~2009: https://en.wikipedia.org/wiki/Mercury_laser https://www.laserfocusworld.com/test-measurement/research/ar... The second link has more details, but they show a 0.7% efficient NIF vs. a 7% efficient Mercury laser in the tiny little chart graphic -- which would reduce the energy for this experiment fr…

Thank you for interesting links. However, I see that the specified pulse energy of a single Mercury laser is 100J vs 18.7kJ for NIF so my point is still valid. There is no way to arrange 20k lasers all pointing at one pellet.
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