2. Background

As aforesaid, nuclear fusion takes place when light atomic nucleus with sufficient kinetic energy collides with each other to combine, overcoming electrostatic force repulsion, to form a heavier atomic nucleus releasing a tremendous amount of energy.

Nuclear fusion reactions have an energy density many times greater than nuclear fission. The nuclear fission involving uranium-235 and plutonium-239 produce more radiation hazards and radioactive waste than the conventional neutronic nuclear fusion involving deuterium and tritium. Both release millions of times more energy than the chemical reactions.

The development of a workable, self-sustaining, highly efficient and controlled nuclear fusion reactor for energy production has been tried for several decades.

To date, no practical nuclear fusion reactor was able to, at the same time, confine and keep the reactants with enough kinetic energy until they fuse at expressive rates and, mainly, release more energy than they consume.

Some reactors with different approaches have been tried: Tokamak, Levitated Dipole, Riggatron, Field-Reversed Configuration, Reversed Field Pinch, Magnetic Mirror Fusion Reactor, Spheromak, Laser Fusion, Z-machine, Focus Fusion, Farnsworth–Hirsch Fusor, Bussard Polywell, Muon-catalyzed Fusion, Heavy Ion Fusion, Magnetized Target Fusion, Colliding Plasma Toroid Fusion, Cold Fusion, Sonofusion, Pyroelectric Fusion and others.

The most promising nuclear fusion reactor design currently being developed and tested is a Tokamak type called ITER (International Thermonuclear Experimental Reactor) which relies on toroidal magnetic field to confine usually a mix of deuterium and tritium. The Tokamak reactors are giants and require a considerable amount of energy, much more than it produces, to maintain the magnetic field and the reactants with enough kinetic energy to fuse. The toroidal magnetic fields confines efficiently in two dimensions, i.e. only radially, allowing plasma rotate longitudinally in a closed path generating loss by electromagnetic radiation (synchrotron radiation) decreasing the plasma kinetic energy lowering the probability of fusion reactions and generates a plasma instability problem due to centrifugal force of particles moving along the curved toroidal magnetic field. Thus, it is inefficient for now due to its technical feasibility, high investment costs and long development time. Most of that one skilled in the area states that, likely, it will not be available before 2050.

The other types of reactor generate nuclear fusion at inexpressive rates (e.g., Cold Fusion) or consume more energy than they produce (e.g., Laser Fusion).

Most of the conventional reactors, e.g. Tokamak, usually are designed to fuse a mix of deuterium and tritium, which gives off 80% of its energy in the form of fast neutrons making the apparatus relatively radioactive. The energy of fast neutrons is collected by converting their thermal energy to electric energy, which is very inefficient (less than 30%).

The Field-Reversed Configuration or Magnetic Mirror Reactor has an unburned fuel leakage problem and the method of direct energy conversion to electricity (e.g.: US patent: 6628740, 6664740 and 6888907), although the best at moment, is relatively very complex and inefficient.

The Farnsworth–Hirsch Fusor (US patent: 3258402, 3386883, 3530036, 3530497, 3533910, 3655508 and 3664920) take advantage of electrostatic acceleration consuming low energy to reach great kinetic energy about 170KeV (2 billion °C) against 10 KeV (100 million °C) of Tokamaks, which uses inefficient methods like ohmic heating. The Farnsworth–Hirsch Fusor, which relies on electrostatic fields for acceleration and confinement, has an unsolvable grid-loss problem, where injected ions create a positively charged cloud around the negative central grid obstructing the remaining of positive ions to reach full kinetic energy leading to a saturation of the reactor.

The magnetic cusps is a common technology among some plasma confinement devices: Magnetic well for plasma confinement (US patent: 4007392), Multicusp plasma containment apparatus - Limpaecher (US patent: 4233537), Plasma confining device (US patent: 4430290), Bussard Polywell (US patent: 4826646) and others.

The Bussard Polywell (US patent: 4826646) is similar to the Multicusp plasma containment apparatus - Limpaecher (US patent: 4233537) in injecting charged particles through magnetic cusps.

The Bussard Polywell (US patent: 4826646 - October 29,1985) wherein method steps, in summary, are generating magnetic cusps, injecting electrons through the magnetic cusps to create a negative potential, injecting positively charged particles toward the negative potential, and maintaining the number of electrons greater than the number of positively charged particles. The required excess of electrons leads to a saturation of the reactor limiting its energy production, also the excess of electrons causes excessive electromagnetic radiation (bremsstrahlung) lowering the kinetic energy of the plasma decreasing the nuclear fusion rate.

In a summary, most of the current nuclear fusion reactor approaches have no technical feasibility; some of them are giant and expensive; most of them are relatively radioactive due of using exclusively deuterium-tritium as fuel; most of them consume more energy than it produces; some of them generate fusion at inexpressive rates; some of them are relatively very complex and inefficient; therefore, no practical solution and no foreseeable end in sight to a practical power plant for all of them at present moment.