August 10, 2010

Very Big Accelerators for Energy Production

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Arxiv - Very Big Accelerators as Energy Producers by R R Wilson of the Fermi National Accelerator Laboratory (3 pages)

One consequence of the application of superconductivity to accelerator construction is that the power consumption of accelerators will become much smaller. This raises the old possibility of using high energy protons to make neutrons which are then absorbed by fertile uranium or thorium to make a fissionable material like plutonium that can be burned in a nuclear reactor. The Energy Doubler/Saver being constructed at Fermilab is to be a superconducting accelerator that will produce 1000 GeV protons. The expected intensity of about 10^12 protons per second corresponds to a beam power of about 0.2 MW. The total power requirements of the Doubler will be about 20 MW of which the injector complex will use approximately 13 MW, and the refrigeration of the superconducting magnets will use about 7 MW. Thus the beam power as projected is only a few orders of magnitude less than the accele ator power. But each 1000 GeV proton will produce about 60,000 neutrons in each nuclear cascade shower that is releaseq in a block of uranium, and then most of these neutrons will be absorbed to produce 60,000 plutonium a toms. Each of these when burned will Subsequently release about 0.2 GeV of fission energy to make a total energy of 12,000 GeV (20 ergs) for each 1000 GeV proton. Inasmuch as megawatts are involved, it appears to be worthwhile to consider the cost of making the protons to see if there could be an overall energy production.

* the emittance of the beam gets better as the energy grows and hence the beam can be transferred to rings of smaller aperture (lower refrigeration costs) as the energy and hence ring size increases
* the number of neutrons produced is roughly proportional to the beam power and this can be made large by increasing both the intensity and the energy of the protons.
* The intensity of an accelerator usually runs into a hard limit imposed by space charge and resonance phenomenon, but the energy can be increased without limit.
* once a proton has gone through the expensive and inefficient business of being produced and accelerated to about 10 GeV energy, then all the energy possible should be pumped into it during the efficient part of the acceleration process that brings it to high energy
* For the Energy Doubler at Fermilab plus all its injector stages, P0 will be roughly 20 MW, and N0 then comes out to be about 2 × 10^13 protons per second. This is about twenty times the expected intensity - but it is far from being unattainable. An intensity of 10^13 protons per second will make about 15 Megawatts of fission energy available; this does not count the energy put into the accelerator. For an overall production of 15 MW, an intensity of 3 × 10^13 protons would be required
* an accelerator that is similar to the Energy Doubler could be made to be energy productive
* The bare-bones accelerator might cost, as a very rough guess, about $200 million for a plant that would produce the fuel to power a 100 MW fission plant. A larger installation might of course cost relatively less per MW.

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