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Non-Statistical Fusion Reactions
In Atomic Scale Accelerators

Brian T. Donovan*

Brian T. Donovan

This is an abstract for a poster to be presented at the
Fifth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.

 

A sub-nuclear resolution microscopic accelerator just a few centimeters long and only a few nano-meter wide might theoretically initiate individually controlled fusion reactions without requiring thermonuclear temperatures or confinement.

In the last few years, researchers have created precise atomic structures using atomic force microscope equipment (piezo electric and magnostrictive crystals used to position sensing probes and atomic position probes). Recently researchers at IBM have created an atomically perfect ring of copper atoms to create an electron standing wave pattern. Other researchers have created various other atomic scale structures such as nano-meter-sized-tubes and Buckminster Fullerenes.

Variations of these structures might be assembled to create an atomic scale particle accelerator capable of accelerating a tritium nucleus and a deuterium nucleus and accomplishing their collision with sub atomic, sub-nuclear, or even sub-proton, accuracy. Conventional fusion reactors are all based on confining the reaction products at a high enough temperature and pressure to achieve a statistical probability of enough high energy random collisions to induce a sustainable fusion reaction. In contrast, individual atoms collided with sub-nuclear accuracy can be induced to fuse with only 51 KeV of energy.

Figure 1 shows a somewhat schematic cross sectional view of the basic atomic scale accelerator. The underlying crystal substrate and numerous technical details have been left out.
Top view
atomic scale
accelerating tube
accelerated nucleus
Axial view
Figure 1.

I understand that this is a highly speculative idea. Apart from the many possible theoretical design problems, formidable obstacles must be overcome before even one device could be built and even more formidable obstacles must be overcome before the millions of parallel units necessary for any significant power output can be built. Nonetheless, the great potential for microscopic fusion reactors deserves attention.

Nuclear fusion with nuclear accuracy atomic scale accelerators does not require extremely high temperatures and confinement required by thermonuclear reactions:

Thermonuclear reactions take advantage of E=(3/2)kT. Thus, using a standard formula for deriving temperature from average molecular collision energy, assuming 10 KeV collisions taking place in a 1015 density plasma the temperature must be:
T=2/3(Joules)/1.38x10-23J/K
T=2/3(104 eV)(1.6x10-19 J/eV)/1.38x10-23J/K
T=77M degrees K

In practice, an ignition temperature of 400M K is needed to compensate for lost energy. For plasmas of 1015 density, this incredibly high temperature equates to particle collisions of a relatively modest 51 KeV. This energy can be imparted using standard electrostatic acceleration or one can add laser or microwave assisted acceleration. Existing 51 KeV accelerators can impart this much energy to colliding ions, but cannot guarantee that many of the ions will actually collide because the beam is wide and atoms are small. If the atoms can individually be accelerated and aimed with sub-nuclear precision, then a high percentage of the ions can collide and fuse. If even only 10% of the ions accelerated actually collided and fused a large net energy gain would be realized.

The potential electrostatic repulsive energy of deuteron centers 3 nuclear radii from each other is 2.72x105 eV from a standard handbook.
E=kQ1Q2/R. Q's are in coulombs and R in meters. k = 9x109
Thus 51 KeV will force deuteron nuclei to overlap closely enough to fuse. By comparison, Tokamaks have reached the equivalent of 20 KeV and the NOVA laser system has reached only 3 KeV particle collision energies.

Practical considerations

Vacuum Breakdown voltage is 1.25MV/cm in vacuum or 125 KV/mm. Thus a 50 KeV accelerator might be as small as 406 Ám long. At these small sizes, other factors may strongly influence the practical length required.

Various recent technological achievements indicate that the accuracy for constructing and aligning the accelerator can be high enough. As mentioned earlier, various atomic structures have been constructed in the laboratory. Several sensing methods also have resolution in the nuclear range, that might facilitate their use for alignment. Capacitance micrometry, for instance, is a very sensitive method for detecting small displacements. This method works by measuring the change in the impedance of a parallel plate capacitor as the spacing or area of the parallel plates changes. Displacements as small as 10 femtometers (10-14m, about the diameter of an electron, or 10,000 times smaller than an atom) can be measured using this technique [1].

The Deuteron ion trajectory can be electrostaticaly deflected. The atoms in the accelerator can be accurately placed on the substrate crystal lattice. The thermally induced vibrations of the accelerator atoms will by averaged out over some 109 atoms. The electrostatic potential on the deflection plates can be adjusted with very high precision including down to the adding and subtracting of individual electrons. The actual frequency of occurrence of fusion events can be used as feedback for the accurate deflection of the accelerated particles.

Production methods:

We can start by looking into direct assembly using piezo or magnostrictive elements and structures similar to those used in Scanning tunneling microscopes and used by other researchers to assemble nanny structures (IBM electron corrals). Much more advanced nano-assemblers will be required and some other method will be needed for any kind of economic mass production. Alternatively substructures can be built using various techniques and then assembled. Subassemblies might include microtubules [3] and thin film coatings (such as MBE). Micro structures could be mass fabricated for most of the accelerator with some misplaced atoms. Then the output end of the accelerator might be assembled atom by atom. This level of accuracy may not be needed since the electric potentials will be used to aim the beams and thus compensate for any small misalignments.

Choice of atomic reaction:

Compared to Deuterium-Deuterium the Deuterium-Tritium reaction ignition temperature is only 4.4 KeV for a reaction energy of 14 MeV vs. an ignition temperature of 48 KeV. for reaction energy around 3.7 MeV. However the Deuterium-Tritium reaction puts out high energy neutrons that destroy the reactor chamber and make it radioactive. The possibility of accelerator based reactions reliably achieving high energy nuclear reactions suggests the possibility of looking at other nuclear reactions that are less radioactive then the deuterium-tritium reaction.

The Deuterium-Deuterium reaction is a good reaction to start with since it is well understood and creates less radioactivity then tritium deuterium reactions. Another disadvantage of tritium is that it must be made in a reactor using lithium and thus is not as common as deuterium.

It would be, of course, be good to eliminate any radioactivity. The following reactions are reported to be completely Non-radioactive:

1H1 + 11B5 => 4He2 + 8.68 MeV. b

Boron 11 and 1H1 are the dominant isotopes and both are common.

Another possible radiation free reaction is:

2H1 + 3He2 => 4He2 (3.6 MeV) + 1H1 (14.7 MeV)

Both reaction products are charged so that direct electrical energy recovery is possible. He3 is rare on Earth: 1.4 atoms per M atoms air. Moon rocks and Jupiter and Saturn have more of it.

Generating useful amounts of power

The energy from each reaction for the Deuterium-Deuterium reaction products is 4 and 3.3 MeV. Taking 3.7 MeV as the energy: 3.7 MeV =2.884x10-18Joules. Thus 3.468 x1017 reactions per second must take place to generate 1 W of energy. Given the speed of the particle particles = [(2*Volts*1.6x10-19)/mass].5, 1 , generating 1 watt with a single accelerator requires a line of 10 meters of hydrogen ions packed 2 radii apart per second. 1 W is also an extremely large amount of energy to dissipate for one nano-meter sized reaction chamber. Thus multi-watt devices will require many multiple accelerators running in parallel.

The energy theoretically available from fusion is of course vast. A 3 GW fusion plant would require .455 grams/day of deuterium, from 13 k Kg/day of sea water. Thus 100KW, a 100 HP car or a couple of American homes for instance, would require 15 mgm/day from just .433 kg of sea water per day.

References And Notes
[1] (FEBRUARY 1994 LASERFOCUSWORLD)
[2] J. J. McClelland et al., Science 877, (931105)
[3] (Science News '94)
[4] Nature 93 IBM Switzerland:researches make electron coral
[5] Laser Focus world 93. (40 nm chromium rows.)


*Corresponding Address:
Brian T. Donovan, postal address with Zip, phone, fax, email: BriTrenth@aol.com



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