In layman's terms, explain what cold fusion is. Has this ever been acheived?  Where?

Hello,

   Nuclear fusion is when two atomic nuclei are brought close enough
together that the strong nuclear binding force can "latch" onto them,
holding them together and making a new nucleus with more protons.
There's an energy difference between the fused nucleus & the two
lighter separate nuclei, which gets released.

   The strong force is very strong, but also only works at very close
range. Before two nuclei can get that close, the mutual electrical
repulsion of the protons tends to push them apart. One known way to
get them close enough for fusion is to ram them together at very high
speed, so that they converge faster than the electric force can
separate them. At that scale high speed = high temperature. This is
hot fusion, such as what goes on in the Sun, or in thermonuclear
weapons. In weapons the high temperature is generated by a nuclear
fission explosive, such as was used against Japan at the end of WW-2.
The fission bomb is jacketed around a core of fusable material. In the
Sun the high temperatures are generated efficiently by the shear
weight of the outer solar layers upon the core, where the fusion takes
place.

   The ongoing problem with making fusion useful is that thus far the
only way we know for sure how to create fusion is with bombs. But they
release all their energy in a tiny fraction of a second. It's not at
all useful as a domestic energy source. The goal of fusion energy
research has been to figure out how to induce sustained fusion which
releases more useable energy than it takes to sustain the reaction. To
this day it continues to cost more energy to run a controlled, slow
fusion reaction than is gotten back. This work continues.

   The idea of cold fusion is to find an alternative way to get nuclei
close together without the "work", i.e., the high energy required by
hot fusion. Now it's time to introduce the "muon". In modern particle
physics there's a class of particles called "leptons", which include
the electron & the moun. The moun is very much like the electron,
having one unit of negative electric charge. But the difference
between them is their masses. The muon is over 200 times more massive
than the electron. But since it's electrically negative, it can in
principle occupy an orbital about an atomic nucleus, just like an
electron. But being 200 times more massive, it can orbit 200 times
closer to the nucleus.

   At that much closer distance it helps to partially negate the
positive electrical charge of the nuclear protons. In theory this
promises to allow the atomic nuclei to approach close to each other
with lower temperatures. One of the problems with this, however, is
that the muon has a very short lifetime before decaying, at which it
becomes useless for promoting fusion. Typically a muon which enters an
orbital tends to spend most of its lifetime in that one "spot", where
it may participate in a few fusions, but doesn't easily break off and
spend some of its lifetime with other nuclei as well, helping to
promote even more fusions.

   So far, it's not a break-even process. No net quantity of useable
wattage has been observed coming from cold fusion.

Comment for qed100.  thanks for your comment.  Please post your
comment as an answer so that you can get paid.  Please tell me.  At
what temperature would cold fusion take place, and how does that
compare with hot fusion?  Has anyone accomplished cold fusion?

The aim of cold fusion research is to produce useful energy from
fusion occuring at temperatures which are roughly around "room
temperature", though this has in some experiments been at the boiling
point of water. Hot fusion, on the other hand, takes place in the
neighborhood of tens of millions of degrees.

   Cold fusion has been done. But it's critical to clarify that no
cold fusion has ever produced more useful energy than has been
invested to prompt the fusion itself. In fact, many physics
laboratories have tabletop fusion devices. These are of course not
used to generate energy, but rather are in use as controlled neutron
generators for other areas of research.

   A particulary notorious claim of successful net energy production
via cold fusion was by Pons & Fleischman in 1989. Unfortunately not a
single specific claim by these gentlemen has ever been verified,
despite a massive industry at the time to independently test the
claims, and most of the scientific community expects that there was
never fusion accomplished in this case.

   As for myself, I'm not an official Google answerer, so it looks
like a freebie for you. ;-)

Qed gave a nice discussion of hot fusion and muon-induced fusion,
which is a form of cold fusion that has actually been observed without
the need for elevated temperatures. He also mentioned that
muon-induced fusion has not resulted in practical energy generation.
It takes a lot of energy to produce muons and each muon catalyzes too
few fusion events to recover that energy.

While the term "cold fusion" is generic, it is most commonly used to
describe the claims of Profs. Pons and Fleischmann, who announced in
1989 that they observed the fusion of deuterium to form helium in an
electrochemical cell with palladium electrodes and a heavy water
electrolyte. Not only that, but they claimed that this process
occurred with hardly any emission of radioactive particles. There was
an initial burst of excitement about their work, but eventually the
work was largely discredited. There are still some believers out
there, but most physicists dismiss the work as unconvincing and, in
fact, a classic example of what Irving Langmuir called "Pathological
Science".

Qed - Your last comment beat me to the punch about Pons and
Fleischmann. I'm glad to see we are in agreement that there was
nothing to it!

"I'm glad to see we are in agreement that there was nothing to it!"

   Indeed. Have you read that book by Gary Taubs about the cold fusion
episode? It's fabulous.

There was a positive outcome to Pons & Fleischmann's announcement, at
least in the UK - a large number of fusion researchers suddenly found
their grants had been approved and they'd got the green light to
proceed.

Ian G.