Interstellar flight by particle beam

Two difficulties with the use of laser-propelled lightsails for interstellar propulsion are the extremely low energy efficiency, and the extremely large lenses required. The energy efficiency can be greatly increased and the required lens size may be greatly decreased by use of a particle beam, rather than a light beam. The particle beam is reflected by a magnetic field on the spacecraft, for example, by a magnetic sail or a mini-magnetosphere inflated by a plasma current. This results in a net force on the sail with no expenditure of propellant, allowing missions of extremely high delta-V, such as an interstellar probe, to be accomplished. Compared to other beam-pushed propulsion systems, the particle-beam pushed sail has the advantages of light weight, high target area, high thermally limited acceleration, high momentum to energy ratio, high beam energy efficiency, and low beam divergence.