Fusion achieved by firing an energetic particle beam at a stationary target — useful for neutron production and diagnostics but inherently unable to produce net energy due to Coulomb scattering losses.
Beam-target fusion occurs when an accelerated ion beam strikes a target containing fusible material. For example, a deuterium beam hitting a tritium target produces D–T fusion neutrons. This is the operating principle of neutron generators, the Farnsworth–Hirsch fusor, and diagnostic neutral beams in tokamaks.[1]
Despite being energetically unfavourable, beam-target fusion is extremely useful: (1) Neutron generators — compact D-T neutron sources for oil well logging, cargo inspection, and materials analysis; (2) SHINE Technologies — uses beam-target D-T fusion for medical isotope production (Mo-99); (3) Fusors — educational devices and neutron sources built by hobbyists and universities.[2]
In thermonuclear fusion (the approach used by tokamaks, stellarators, and ICF), the entire fuel is heated to fusion temperatures so that reactions occur between thermal particles moving in random directions. This avoids the beam-energy loss problem because Coulomb collisions thermalise the plasma rather than being wasted.[3]