In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation. The concept has more recently been referred to as an accelerator-driven system (ADS) or accelerator-driven sub-critical reactor. None have ever been built. History The concept is credited to Italian scientist Carlo Rubbia, a Nobel Prize particle physicist and former director of Europe's CERN international nuclear physics lab. He published a proposal for a power reactor (nicknamed "Rubbiatron") based on a proton cyclotron accelerator with a beam energy of 800 MeV to 1 GeV, and a target with thorium as fuel and lead as a coolant. Rubbia's scheme also borrows from ideas developed by a group led by nuclear physicist Charles Bowman of the Los Alamos National Laboratory Principle and feasibility The energy amplifier first uses a particle accelerator (e.g. linac, synchrotron, cyclotron or FFAG) to produce a beam of high-energy (relativistic) protons. The beam is directed to smash into the nucleus of a heavy metal target, such as lead, thorium or uranium. Inelastic collisions between the proton beam and the target results in spallation, which produces twenty to thirty neutrons per event. It might be possible to increase the neutron flux through the use of a neutron amplifier, a thin film of fissile material surrounding the spallation source; the use of neutron amplification in CANDU reactors has been proposed. While CANDU is a critical design, many of the concepts can be applied to a sub-critical system. Thorium nuclei absorb neutrons, thus breeding fissile uranium-233, an isotope of uranium which is not found in nature. Moderated neutrons produce U-233 fission, releasing energy. This design is entirely plausible with currently available technology, but requires more study before it can be declared both practical and economical. OMEGA project () is being studied as one of methodology of accelerator-driven system (ADS) in Japan. Richard Garwin and Georges Charpak describe the energy amplifier in detail in their book "Megawatts and Megatons: A Turning Point in the Nuclear Age?" (2001) on pages 153-163. Earlier, the general concept of the energy amplifier, namely an accelerator-driven sub-critical reactor, was covered in "The Second Nuclear Era" (1985) pages 62–64, by Alvin M. Weinberg and others. Advantages The concept has several potential