TRAIL: A Tokamak rail gun limiter for fusion reactors

An attractive new limiter concept is investigated. The Tokamak Rail Gun Limiter (TRAIL) system impacts a stream of moderate velocity pellets (100 to 200 m/sec through the plasma edge region to absorb energy and define the plasma boundary. The pellets are recycled, after cooling, to the injector in an E-M mass accelerator. Heat fluxes of\sim30,000W/cm²can be readily accommodated by the pellets, with very low recirculating power requirements (∼0.1%) for the accelerator. The mass accelerator velocity requirements are well within the present state-of-the-art (several km/ see). Accelerators injecting pellets at ∼1 km/sec can be used to control local plasma temperature and current profiles and to act as energy absorbers to shut down the plasma without damage to the first wall if a plasma disruption occurs.