The problem of the penetration of a neutral atomic beam and a cluster ion beam into a fusion plasma is reviewed. The short penetration length of an atomic beam, coupled with certain geometric dependences of the magnet coil costs, implies an optimum injection energy for a D-T mirror fusion power system in the range 200 to 300 keV. The penetration length for a cluster beam is inferred from available data. For certain charge and mass distributions of the cluster fragments, a substantial improvement of beam penetration is possible, allowing for injection as low as 100 keV per deuteron. Additional fragment charge and mass distribution data will be necessary, however, to clarify the role of cluster injection.
Search for nuclear fusion in deuterated targets under cluster-beam impact