Back to fusion. When two hydrogen nuclei fuse, they release nuclear energy. Hydrogen is an element at the lower end of atomic numbers, where fusion releases energy, at the high (uranium) end energy is released by fission. Fusion takes place when two nuclei get very close to each other, but that is difficult to achieve, because their positive charges repel each other. For fusion to take place, the hydrogen has to be at a sufficiently high temperature and a suf-ficiently high pressure for a sufficiently long time.
No vessel can contain a gas under the required temperatures and pressures, and one way, which has proven very expensive without bringing the hoped for results, is magnetic confinement by Tokamaks and other magnetic configurations that can hold a hot hydrogen plasma in place.
The other basic method is inertial confinement. The fuel is enclosed in a small plastic capsule or pellet and very short laser pulses of enormous energies (kilojoules) deliver their wallop simultaneously from many pairs of opposite directions. The volume inside the pellet will then do what it would do under simul-taneous hammer blows from all directions (if there were room for hammers); it will be compressed to a smaller size or "implode" (the plastic container pellet will simply burn off). If the diameter of he sphere is compressed to 1/10 of its size, the pressure will rise a thousandfold, and the temperature will skyrocket. If the product of temperature, pressure and their duration exceed a critical value, some nuclei will fuse and the released energy will make other nuclei fuse; the hydrogen will "ignite."
This much has been reported in these pages since June 1974, including the development of the world's most powerful laser, the Nova at Lawrence Livermore Lab, which last year reached a net output of 70 kilojoules in its pulse of blue light hitting the pellet from 20 directions. The individual beams come from the beam of single laser via beamsplitters and special mirrors which can with-stand the onslaught of such quantities of light.
But the total energy in the pulse is not the only parameter that assures success. ("Scientific breakeven" is reached when the ener-gy given out by the pellet exceeds the input energy of the laser light pulse; it has not yet been achieved, though it is close now). There is the shape of the pulse and several other parameters that have to be adjusted to their optimum value
¾if it is known. Further upgrad-ing of the Nova to the "Precision Nova" is now proposed. It will, among other improvements, have no more than 5% to 10% imbalance in power among the various directions from which the beams hit the pellet (with insufficient balance, the pellet will totter between successive hammer strikes instead of being compressed by their simultaneous delivery), and the precision of the direction of the beam will lie within an angle of 10 microradians or 0.000057ø, or in astronomic measure, about 0.2 seconds of arc.
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Vol. 18, No. 1
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 18, No. 1 Date: December 01, 2004 03:53 PM Title: An opportunity
Copyright © 2004 - Access to Energy Newsletter Archive
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