Commissioning of the Pegasus-III Experiment

The Pegasus-III Experiment is a solenoid-free spherical tokamak dedicated to comparative non-solenoidal tokamak startup studies. Major upgrades to its magnets and power systems have increased B_T four-fold to 0.6 T for up to 100 ms with improved shape control while maintaining low A ~ 1.2. This increased field directly supports the mission of researching non-solenoidal power plant-relevant startup techniques such as local and coaxial helicity injection and RF wave injection. The Ohmic solenoid has been removed and the toroidal field system now is comprised of a new 24-turn center rod and outer coil system, torque assemblies with crossover finger joints, and integrated divertor coils. Approximately 175 MVA of programmable power systems and 8.5 MJ of stored energy are available to drive the four-fold toroidal field increase, new divertor and poloidal field coils, and local and coaxial helicity injectors. The digital control system uses FPGA technology and real-time computing to control the electromagnets and helicity injectors while providing fault detection and protection. The commissioning and initial operation of these systems of Pegasus-III, as well as results from the first LHI physics campaign, will be reported.