Neutral beam accelerators have been explored for practical fusion by smashing deuterium atoms, with the latest attempt being the SIGFE experiment at the University of Wisconsin, which ultimately failed due to neutron production from spallation rather than fusion. Discussions highlight the challenges of ionization for acceleration, as neutral atoms cannot be accelerated without becoming ions, raising questions about the necessity of complete ionization. The Polywell device is mentioned as a potentially simpler and cheaper alternative to traditional Tokamaks, although it still requires superconducting magnets and vacuum conditions. Theoretical calculations suggest that achieving high ion densities is crucial for practical fusion, with estimates indicating that currents over tens of Amperes may be needed. Overall, while various methods and concepts are being explored, significant challenges remain in achieving sustainable fusion energy.