Problem with laser initiated fusion

bwilson4web · Jan 12, 2014

Looking for more details about UK efforts in laser initiated fusion, I found this:

COVENTRY and OXFORD, England – A new strongly heated graphite experiment has left an international team of researchers with some unexpected results that may reveal secrets of . . . laser-driven fusion. In an attempt to learn more about how energy is shared between the different species of matter – especially how it is transferred from strongly heated electrons to the heavy ionic cores of atoms that have been left to cool – scientists from the University of Warwick and Oxford University were left with some puzzling new results. The findings could lead to a revised understanding of the life cycle of giant planets and stars.
The difference in temperatures between the hot electrons and cooler ions should level out quickly as the electrons interact with the ions; the time it takes to reach a common temperature is a good measure of the interaction strength between the two. This interaction also defines, for instance, how heat or radiation is transported from the inside of a planet or star to its surface and, thus, planetary and stellar evolution. The process is also essential for nuclear fusion where the electrons are heated by fusion products, but the ions need to be hot for more fusion to occur.

. . . the Warwick and Oxford team devised a more precise experiment that employed intense proton beams created via a novel laser-driven acceleration scheme, rather than direct heating by a laser. Heating by the protons resulted in better-defined conditions because the protons heat only the electrons but for the entire sample.
As a result, the researchers obtained a clean sample with electrons at 17,000 K while the ions remained at about 300 K (around room temperature). Rather than eliminating the gap between the model and the observed results, the scientists discovered that this method significantly increased the difference. The more precise experiment showed that the equilibration of the temperatures for hot electrons and cool ions was actually three times slower than previous measurements and more than 10 times slower than the model predicted.
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Source:
Hot graphite shines new light on laser-driven fusion | Tech Pulse | Mar 2013 | Photonics Spectra

Now it makes sense why laser initiated fusion has been unproductive. The light interacts with the electrons, not directly with the protons. So in effect the electron shells heat up quite nicely but the nucleus, a substantially heavier structure, remains relatively, inertially at rest while the electron shell rapidly loses energy. In effect, the nucleus is surrounded by an electron-shell, pillow.

Bob Wilson

Problem with laser initiated fusion

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Problem with laser initiated fusion

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