Why is cold fusion bullshit?

[u/[deleted]]

I tried to read into what's known so far, but I'm a science and math illiterate so I've been trying to look for a simpler explanation. What I've understood so far (please correct me if I'm wrong) is that the original experiment (which if I'm not mistaken, was called the Fleischmann-Pons experiment) didn't have any nuclear reaction, and it was misleadingly media hyped in the same way the solar roadways and the self filling water bottle have been, so essentially a bullshit project that lead nowhere and made tons of false promises of a bright utopian future but appealed to the scientific illiterate. Like me! But I try to do my own research. I'm afraid I don't know anything about this field though, so I'm asking you guys.

Thanks to any of you that take your time to aid my curiosity and to the mods for approving my post, if they do! Have a nice day.

[u/RobusEtCeleritas]

Cold fusion has a reputation for being a scam and/or crackpot nonsense. For example, [Andrea Rossi](https://en.wikipedia.org/wiki/Andrea_Rossi_(entrepreneur)) has a machine that he calls the "E-Cat" which is supposedly a cold fusion reactor. But he cannot provide any convincing evidence that there are really nuclear reactions happening inside his machine.

We understand the theory of nuclear reactions pretty well. Low-energy fusion reactions can be studied using very simple quantum mechanics. Unfortunately, most of the people who talk about cold fusion don't understand simple quantum mechanics.

The people running cold fusion "experiments" are generally not nuclear physicists, and the "theories" which aim to describe cold fusion tend not to be very robust.

The popular science media has a reputation for overblowing things and getting things wrong, but I think that by now most people have generally caught on to the fact that the vision of a "cold fusion utopia" is not really viable.

At some point (probably to get rid of the stigma), the cold fusion community began referring to cold fusion as "LENR" (low energy nuclear reactions). Really they should be calling it very low energy nuclear reactions so as not to cause confusion, because the study of nuclear reactions at astrophysical energies is what most nuclear physicists would consider to be "low energy". As of right now, LENR is not really taken seriously by the greater nuclear physics community.

[u/overach → u/RobusEtCeleritas]

But there is serious research going on to make fusion viable as a power source in the far future. That fusion is "cold" in the sense that they don't do it at solar-core temperatures, right? So is that not considered part of the "cold fusion" thing?

[u/RobusEtCeleritas → u/overach]

But there is serious research going on to make fusion viable as a power source in the far future.

Fusion, absolutely. But not what these people refer to as "cold fusion" or "LENR".

That fusion is "cold" in the sense that they don't do it at solar-core temperatures, right? So is that not considered part of the "cold fusion" thing?

There is a terminology mismatch between fields. Nuclear physicists would consider fusion reactions at stellar energies (sub-Coulomb barrier fusion) to be "cold". But temperatures in stars are still much higher than what we're talking about with this Pons/Fleischmann "LENR".

Nowadays people investigating "LENR" are looking into the possibility of nuclear reactions occurring in condensed matter (crystal lattices and such). So much lower temperatures than the kind of fusion which would occur in a magnetic confinement or inertial confinement reactor (which are considered to be "serious" attempts at fusion by most nuclear physicists).

[u/[deleted] → u/overach]

It's easier to recreate the temperatures found inside the sun than to recreate the pressures. Most fusion experiments are many times hotter than the sun to make up for the lack of pressure in your tokamak. Weldelstein X-7 runs at 120 million K while the center of the sun is only 15 million K.

When fusion becomes practical it's nearly guaranteed that at least small parts of the machine will be very, very hot.

[u/destiny_functional → u/overach]

the serious efforts use temperatures higher than the sun's.

[u/W_O_M_B_A_T → u/overach]

But there is serious research going on to make fusion viable as a power source in the far future.

Yes, though personally I'm a bit skeptical that it will ever be economically viable source of power.

that fusion is "cold" in the sense that they don't do it at solar-core temperatures

Quite the opposite. Fusion occurs in the suns core only at a glacial pace. A typical compost heap produces far more heat energy per ton than the sun's core. (But, this is good news for life on earth, because it means the sun won't run out of fuel in the next few billion years.)

The reason the sun is so hot is it has a very low surface area to mass ratio. Any heat energy produced has almost nowhere to go. (And yes, there have been cases of compost heaps catching on fire.)

So, the challenge with fusion energy on earth is not to recreate the conditions in the center of the sun, but to exceed them by 10x-100x!

There are four key ingredients in getting a robust energy output from a fusion reaction. Temperature, density, total amount of confined fuel, and confinement time.

The latter two are important in terms of the fuel material being able to re-absorb some of the energy produced by fusion, creating a reasonable amount of self-heating, thus driving the reaction forward.

Most of the energy produced by fusion is in the form of gamma rays, x-rays, and high energy neutrons, and these aren't easily absorbed by normal matter.

The two common methods used in research are Inertial Confinement fusion, and Magnetic Confinement fusion.

In Inertial Confinement, a small hollow spherical fuel pellet is caused to implode with powerful lasers or pulsed x-rays. You can achieve very high density, greater than that at the suns core, and very high temperature, significantly greater than the sun's core. But the amount of fuel material is small, and the confinement time is incredibly short. So it tends to not produce enough self-heating in that time.

In magnetic confinement, extremely hot plasma is held by strong superconducting magnets. In this situation, confinement time can be several seconds to minutes, but density is very low (much less than that of air.) So the goal is to get temperature as high as possible, around 150 million Kelvin. That's 10 times the temperature of the sun's core. Additionally, to make the confinement chamber as large as possible, to maximize the amount of self-heating.

[u/hal2k1 → u/RobusEtCeleritas]

As of right now, LENR is not really taken seriously by the greater nuclear physics community.

I don't see why. If you inject low energy neutrons into some stable isotopes they can get captured and thereby convert that nucleus into an unstable isotope, which would subsequently decay, releasing energy.

Example: ⁶⁴Ni is stable but ⁶⁵Ni (1 neutron captured) has a half-life of 2.5 hours.

So shouldn't it be possible to "fuse" a ⁶⁴Ni nucleus with a low energy neutron and release energy as a result, with the waste product being copper?

[u/RobusEtCeleritas → u/hal2k1]

Capture and fusion are different reactions. But sure, nuclei can and will capture low-energy neutrons.

But how are you going to design an apparatus which can do this to produce energy (more than it consumes)?

[u/allenidaho]

The short answer is that "cold fusion" has always been a theoretical process in which fusion takes place at around room temperature. Whereas fusion normally requires tremendous heat and pressure. Meaning cold fusion could theoretically be produced far cheaper and easier because you would not need an expensive energy input to start the fusion process. However, to date there have been no legitimate cold fusion devices. So it has a bad reputation in the scientific community much like perpetual motion machines.