The Cit Pellet Injection System: Description and Supporting

The Compact Ignition Tokamak (CIT) will use an advanced, high-velocity pellet injection system to achieve and maintain ignited plasmas. Two pellet injectors are provided: a moderate-velocity (1 to 1 S-km/s), single-stage pneumatic injector with high reliability and a high-velocity (4to 5-km/s), two-stage pellet injector that uses frozen hydrogenic pellets encased in sabots. Both pellet injectors are qualified for operation with tritium feed gas. Issues such as performance, neutron activation of injector components, maintenance, design of the pellet injection vacuum line, gas loads to the reprocessing system, and equipment layout are discussed. Results and plans for supporting research and development (R&D) in the areas of tritium pellet fabrication and high-velocity, repetitive two-stage pneumatic injectors are presented. SYSTEM PERFORMANCE REQUIREMENTS Performance requirements for the pellet injection system were developed in collaboration with CIT physics and project staff to ensure sufficient performance for the ignition mission while minimizing impact on the isotope reprocessing system and local tritium inventory levels. Another consideration was the requirement to develop the supporting technology in time for design, fabrication, and testing of the system at Oak Ridge National Laboratory (ORNL), followed by installation on CIT by the first-plasma milestone. This time constraint eliminated some of the more exotic methods of plasma fueling, such as electron-beam pellet ablation and compact toroid fueling, from further consideration. The specifications of the CIT pellet injection system' are given in Table I.