Tokamak start-up

During recent years, improvements have been made to tokamak start-up procedures, which are important to the optimization of ignited tokamaks. The use of RF-assisted start-up and noninductive current drive has led to substantial reduction and even complete elimination of the volt-seconds used during start-up, relaxing constraints on poloidal coil, vacuum vessel, and structure design. This paper reviews these and other improvements and discusses the various bulk heating techniques that may be used to ignite a D-T plasma. New results show that with lower hybrid preionization and current drive, the voltage may even be reversed. Brief comments are offered on ohmic ignition, though the paper concentrates on the use of ignition tokamaks that require auxiliary heating to ignite. The most successful approaches to the auxiliary (nonohmic) heating of tokamaks are the injection of intense neutral atom beams, the application of RF heating and adiabatic compression, in addition to the use of solid hydrogen pellet injection. Each approach is discussed