(Based on research done by A.G.Ruggiero of Brookhaven Nat.Lab.)
It has been suggested that the fusion reaction between protons and ions of boron-11 is most desirable because of the complete absence of dangerous byproducts - no neutron or gamma radiation is involved. Moreover, it is possible to harness electric power directly from the reaction process because the final product are 3 alpha-particles (and carbon-12).
Due to the high Coulomb barrier, this reaction requests new accelerator technology to be achieved. A.G.Ruggiero of BNL proposed to use newly developed concept of Crystalline Beam to overcome that obstacle. By this technique it is possible to obtain more compact beams in which, most importantly, particles occupy well-defined rigid positions, thus extremely increasing luminosity.
General sketch of the appropriate accelerator design (click on the picture for larger version).
In order for proton-boron-11 reaction to occure and produce three alpha particles and carbon-12, collision at center-of-mass energy of 675KeV (with a width of about +/- 75KeV) is neccessary. This resonance exibits large, 0.9 barn, cross-section. Once reaction is acheived, 8.7 MeV of energy is released as kinetic energy of 3 alpha particles which are emitted. This energy is easy to "harvest", for example by a series of concentric torodial electrodes placed around the axis of accelerator.
Crystalline Beam method of achieving this reaction requires to circulate ions of Boron at charge +3 and Hydrogen ions with charge -1 in opposite directions in the Crystalline Beam accelerator. Crystalline Beam state should be acheived by Laser Cooling technique. In order for this method to work, one needs to have ions with electrons, instead of the simple proton and boron-11. It can be shown that if accelerator is designed as one bent and closed onto itself Circular RF Quadrupole with diameter of 2.5 m, energies of the "proton" and "boron" beams should be 0.368MeV and 0.307 MeV, respectively.
It has been calculated that a "break-even" mode (invested energy: like ion sources accelerator magnets and laser cooling equal to released fusion power) - assuming 80 % efficiency, is reached for Crystalline Beam state n=24, ie. sizes of proton and boron beam of 10 cm and 15 cm radius. Under same assumption, 10KW NET energy is produced in states n=26, with beam diameters of 20cm and 30cm respectivly. These specifications are reasonable at todays state of accelerator technology. However, developement of the Crystalline beam technology is at its first steps.
As final notice, fusion power generator conceptually described here for 10KW output can fit in the area of less than 10 square meter (less than 90 square ft.) and does not produce any harmfull byproduct. Will we see them sometime at our homes? (It is possible to designe this system somewhat larger, but for hundreds of MW of power, usuall in large powerplants of today, one would have to have multitude of small units. one large unit is not compatible with the method described here).
Cross-section of eventual Crystalline Beam (click on the picture for the larger version):