National press reports that successful experiments in cold fusion research in the US could lead to a new clean source of energy are unfounded.
Claims that work carried out by the US government’s Oak Ridge National Laboratory, Tennessee, could point the way to the Holy Grail of an abundant and clean source of energy are false, according to Dr Thornton Greenland, a leading fusion expert. He was commenting on papers to be published by the US team today in the journal Science, which fall short of drawing conclusions about the potential for cold fusion power plants.
In cold fusion, the object is to create a sustained chain reaction in which atomic nuclei fuse at room temperature to produce more energy than was needed to start the process. As yet this has never been achieved.
Greenland, who is adviser to the UK Atomic Energy Authority and the European fusion power project, Joint European Torus, at Culham, Oxfordshire, said the latest US experiments do not represent a great scientific advance and would have few applications.
‘This is not cold fusion. It is hot fusion. The temperatures they are claiming to get arecomparable to those found in JET which are 10 million degrees C. Neither can you say it’s a big breakthrough for this research. The new work in this is that you might be able to manipulate bubbles in a liquid.
‘But it solves none of the real problems, the main one being the inability to sustain the process. Only by keeping it going will more energy be produced than was used to start it.’
Fusion is how the sun generates its heat and light. It fuses hydrogen at temperatures of 10 million degrees C and produces helium as a by-product. This is hot fusion as opposed to cold fusion where nuclei bond at room temperature and below.
So far laboratories have achieved only a few seconds of hot fusion, generating far less energy than was used to start the process. Only a sustained chain reaction of fusing atomic nuclei could provide more energy over time than was used in ignition. Scientists hope to achieve this with the next generation of hot fusion reactor, called Iter, a project involving Europe, Canada, Japan and Russia.
It should operate for five to 10 minutes at a time and generate 10 times more energy than was used to ignite the process. It is considered to be the stepping stone to commercial power stations, thought to be 40-50 years away.
But the experiments carried out at Oak Ridge and the Russian Academy of Sciences do not amount to a sustained reaction. The scientists have only concluded that fusion could be occurring briefly because neutron emissions and the fusion by-product tritium were detected.
The Oak Ridge process uses acoustic cavitation, where the pressure of a sound wave creates and then collapses a bubble in a liquid. The first sound wave stretches the liquid, creating a bubble, then second-compresses it causing a chemical reaction, releasing a flash of light. This is known as sonoluminescence. It is a theory that has existed for decades.
In the Oak Ridge experiment the liquid is a deuterium acetone, where the acetone’s hydrogen atoms have been replaced with deuterium. This is a heavy form of hydrogen that occurs naturally in sea water.
As the pressure waves strike the deuterium atoms the nuclei fuse in sun-like temperatures. But none of this is particularly new.
Previously tabletop fusion using an atomic accelerator has fused deuterium with tritium and produced more energy than the Oak Ridge experiments.
The trail for the Holy Grail has gone cold…
Scientists have searched for the means to produce cold fusion because it represents the perfect answer to the questions of future energy sources and global warming.
Instead of burning fossil fuels or producing mountains of radioactive waste from nuclear fission, fusion releases the energy that is bound up in atoms themselves.
Although this process takes place at 10 million degrees C in the sun, and it is possible to produce it at such temperatures in the laboratory, scientists seek to repeat it at more reasonable temperatures.
The idea is to set up a sustained chain reaction that produces more energy than is used to kickstart the process. As such, cold fusion would provide a virtually unlimited and clean source of power.
However, in more than 40 years of experimentation no one has come close, and given our current understanding it is doubtful that anyone ever will.
Leading fusion expert Dr Thornton Greenland is an authority on cold fusion technology, or muon catalysed fusion as it is known. ‘The Russians investigated this from 1947 onwards. It can be done at very low temperatures,’ he said.
A muon, which is a naturally occurring elementary particle, is captured using a particle accelerator. It is then injected into a chamber of hydrogen or deuterium gas molecules that are under high pressure.
‘The muon will collide with a molecule, knocking out an electron so causing the molecule to shrink. This brings the hydrogen molecule’s atomic nuclei into close proximity – at which point they fuse.’
But while fusion is achieved, the process is unable to sustain itself and produce energy, which is the fundamental problem.
Muons decay in a few microseconds, said Thornton. Just to release as much energy, through fusion, as was used to capture it, would require 1,000 collisions. Often a muon can only achieve a few hundred.
The particle either dies too quickly or becomes ‘stuck’ to one of the molecules it collided with and is unable, before it decays, to strike another.
So although cold fusion was attractive to scientists because it was theoretically easier to operate than hot unstable plasma fusion, it now holds little promise.