A fusion reaction that does not produce neutrons, e.g. proton-boron fusion. The neutrons produced during fusion activate the surrounding material and carry away most of the fusion energy, so it is advantageous to achieve aneutronic fusion, which does not produce neutrons. The resulting particles can then be held in the magnetic field and their energy can be efficiently used. However, aneutronic fusion needs much higher ignition temperatures than, for example, neutron-producing deuterium-tritium fusion.