BalderSion
BalderSion t1_j0ugo13 wrote
Reply to comment by vegiimite in How do X-rays “compress” a nuclear fusion pellet? by i_owe_them13
Yeah, and that's probably a fair assessment. Fusion is an optimist's game. For non optimists, the promise is too great to ignore, but it took decades just to get our arms around how difficult it was going to be; hence the fusion is 50 years away and always will be reputation.
I would take this result as proof ICF can generate power, not that it's ready to. I mean, we knew from hydrogen bombs it was possible to get Q>1 from inertial confinement, but not if it could be done with beams like this. Similarly, if ITER gets their Q>10 result in the next couple of years, I would take that as evidence that magnetically confined burning plasmas can be stable, so we'll know MFE can generate power, not that it's ready to.
BalderSion t1_j0u6rwl wrote
Reply to comment by JanB1 in How do X-rays “compress” a nuclear fusion pellet? by i_owe_them13
Right. It's true that photons have momentum, but not much as these things go. It's rather more efficient that the photons boil the outer layer, and the reaction force from the gases boiling off push the pellet inward radially.
This sets up a situation where a light fluid is pushing against a heavy fluid (not unlike putting vinegar on top of oil in a salad dressing) so a slight nonuniformity amplifies because of the Rayleigh–Taylor instability, so some of the fuel squirts out, rather than compress uniformly and your target won't fuse. This is why the targets have to be so smooth and the radiation needs to be uniform.
There are some so called fast ignition schemes that aim to relax these requirements, but they haven't been demonstrated yet. We're on the path.
BalderSion t1_j0twoza wrote
Reply to comment by Graekaris in How do X-rays “compress” a nuclear fusion pellet? by i_owe_them13
Ablation pressure is basically the rocket equation. Radiation boils off the outermost layer, pushing that layer away from the pellet as a gas with some thermal energy. Equal and opposite reaction pushes the pellet in the opposite direction. Now make this evenly around the pellet and all the pellet can do is compress into a higher density.
BalderSion t1_j0tpoqf wrote
Reply to comment by Jon_Beveryman in How do X-rays “compress” a nuclear fusion pellet? by i_owe_them13
It's funny, because I have high confidence they can, and low confidence how. Just exposing my bias. Of course, I expected this result from NIF 10 years ago.
The challenge is likely to be uniformity rather than pressure. Presumably this can be addressed, but again I don't know much about the how.
BalderSion t1_j0tgpko wrote
Reply to comment by vegiimite in How do X-rays “compress” a nuclear fusion pellet? by i_owe_them13
So I was in the fusion technology field in grad school 10 years ago, but there are a couple of things here I'd like to address.
In the conceptual ICF reactor studies we and other groups put out, the rep rate was 10 Hz, not less than 1 Hz. For a less than 1 Hz rep rate you'd need much bigger pellets, that are driven much higher beam energy to maintain the power output. Also plant efficiency goes up with rep rate.
The good news is you can inject the pellet at 10's of metres per second. A compression and fusion burn wave will be over in nano seconds and still maintain their center of mass velocity, so the resulting expanding plasma can clear the chamber in time for the next shot, if the engineering is done right.
Also, in the field, for a fusion powerplant it is well recognized the plant will need to be direct drive, that is the driver (particle beam or laser) will need to be incident on the pellet directly, rather than use the hohlraum, because the cost per shot needs to be on the order of 25¢ per shot to be cost effective. NIF used a hohlraum to relax the driver requirements, but direct drive is another hurdle to overcome on the way to ICF fusion.
BalderSion t1_iykadsb wrote
Reply to comment by BodolftheGnome in Gold from ancient Troy, Poliochni and Ur had the same origin by IslandChillin
As I understand it, a key way to differentiate a neanderthal camp from a homo sapien camp is the the neanderthals only have locally sourced materials and homo sapiens have goods from all over Eurasia.
BalderSion t1_itxuj5y wrote
Reply to comment by Sprucecaboose2 in Aaron Rodgers, “Critical Thinking,” and Intellectual Humility by ADefiniteDescription
I understand why Rodgers' opinion was reported on. It impacted whether the team was going to win, therefore it was sports news, and in parts of Wisconsin sports segments are more than half of the 5, 6, and 10 o'clock news reports.
What frustrated me was that no reporter asked the simple question, "What evidence would change your mind?". It's such a simple question to ask, and would completely reveal if he was engaging in honest skepticism or using the language of a skeptic as cover for an indefensible position.
BalderSion t1_j12ukvz wrote
Reply to comment by EBtwopoint3 in How do X-rays “compress” a nuclear fusion pellet? by i_owe_them13
A fusion plant would be the same steam generator. The engineering is mature, and it's the most efficient way to turn hot into electricity. The D+T fusion reaction produced puts 80% of its energy into a neuron and 20% into a helium. Both will strike the wall of the chamber and that will heat the chamber. Cooling channels running through the wall carry the heat to a heat exchanger which makes steam for the turbine. Any other mechanism would be less efficient than steam generator.
There are the p+Boron 11 schemes that produce energetic charged particles (no neutrons), which could be, magnetically funneled into collectors to create a very high voltage DC current, however the physics challenges with that fusion reaction are higher.