Hacker News Reader

Comment by vikramkr | Hacker News Reader

For anyone with experience in nuclear physics/fusion - how big a deal is this? I know that hard-tech findings tend to get, well, "selectively" presented to the public (I see at all the time in biotech), so I'm curious if this is actually a big deal? As in, does this phenomena (perhaps not in this form, but using this as a starting point) actually have the potential that people think of when they think "cold fusion" or "easy fusion power?" Or is there something missing in the reporting?

View on HN

I got my undergrad in Engineering Physics from CU-Boulder and talked with many professors about fusion research (plus keeping up with developments since then).

Putting aside all the controversy of LENR (low-energy nuclear reactions, the official name for cold fusion) and assuming that the theory actually results in usable tech (for once), the first line of the NASA article hints at where a device's power density would be competitive:

> "A team of NASA researchers seeking a new energy source for deep-space exploration missions"

which tells me that a theoretical device would be a replacement for current RTGs [1]. Low but consistent power for niche applications.

But in general I wouldn't get your hopes up. The higher-energy types of fusion power are far more promising for world-wide civilization-powering clean energy.

[1] https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

The part that I'm not grasping about this is how you harness the power that is created. I think it's great that they can start a fusion reaction this way. But how does this become practical, in theory? Does the lattice radiate heat once fusion starts or something?

Looking at the provided fusion flowchart: https://www1.grc.nasa.gov/wp-content/uploads/Steinetz-Fusion...

It appears to be the same mechanism as neutronic high-energy fusion. An energetic neutron gets kicked out, which collides with some material in the cell (probably the erbium lattice), and generates heat. Which then needs to be hooked up to a water boiler to create steam, which powers a turbine, etc.

I'm much more hopeful for someone creating a Dense Plasma Focus device with aneutronic hydrogen-boron (pB11) fuel because the reaction energy can be directly captured as electricity, instead of having to capture hot neutrons to boil water.

If the goal is a RTG, the thermal energy would likely be converted directly to electricity with a thermoelectric element.

Fusion products have particle energy on the order of 10s to 100s of MeV. Thermal machines tend to melt or evaporate when their average particle energy gets on the order of 100s of meV.

The increase in entropy on that temperature conversion alone is absurdly wasteful.

My understanding is that they are talking about bulk heating of a metal carrier, probably by a tens to low hundreds of degrees for power production. Not every particle in the medium is at Mev, otherwise it would be trillions of degrees kelvin.

In direct conversion, all of the particles used on the conversion have MeV energies. It is exactly that bulk heating that is the problem.

When you get a very low entropy source and your first step on using it consist on increasing the entropy 1000000000 times, you lose a lot of flexibility and efficiency.

Nuclear fusion is pretty much the exact opposite of a low entropy source. In any case, thermal power plants (gas, coal or nuclear) reach up to 50% efficiency with modern gas or steam turbines.

Basically, this isn't really what people have thought of historically as cold fusion, because you are hitting the deuterons with photons which have high enough energy that you would expect to see some neutrons anyways (and making those high energy photons costs a whole lot of energy). The big thing in the paper is that they are seeing some higher energy neutrons than you would expect to see. The 2.5 MeV neutrons are pretty normal for whacking deuterons around. The question is why they are getting 5 MeV neutrons from this reaction.

I don't have time today to dig into the theory which they have which predicts the high energy neutrons. If there is a benefit from this experiment, it would be in validating the theory. Perhaps the theory could point a way toward lattices helping fusion along, in a similar way that Fleishman and Pons thought it could. However, that is a long step from this experiment, and it is possible that there is some other cause for the high energy neutrons other than the lattice screening effect.

There's a rule in physics that "the impossible doesn't happen very often". What's more likely, a stunning unexpected discovery, or a subtle experimental error?

> There's a rule in physics that "the impossible doesn't happen very often". What's more likely, a stunning unexpected discovery, or a subtle experimental error?

You're implying that a a subtle error would be sufficient to explain the observations, which doesn't seem to be the case here.

Gross experimental or interpretation errors are a possibility, of course, but are correspondingly less likely.

> which doesn't seem to be the case here.

That's the thing about subtle errors. They never seem to be the case, even when they are the case. Remember the superluminal neutrino claim a few years back? There are endless ways an experiment can go awry and present misleading results.

Here, there's going to be a very large background (of neutrons and photons) from the process they are using. I wonder if they didn't handle background subtraction quite right.

Reply on news.ycombinator.com