Development of a compact torus injection system for the Keda Torus eXperiment

A compact torus injection system, KTX-CTI, has been developed for the planned injection experiments on the Keda Torus eXperiment (KTX) reversed field pinch (RFP) device to investigate the physics and engineering issues associated with interaction between a compact torus (CT) and RFP. The key interests include fueling directly into the reactor center, confinement improvement, and the injection of momentum and helicity into the RFP discharges. The CT velocity and mass have been measured using a multichannel optical fiber interferometer, and for the first time the time evolution of the CT density profile during CT propagation is obtained. The effects of discharge parameters on the number of injected particles, CT velocity and CT density have been characterized: the maximum hydrogen CT plasma mass, m_CT, is 50 μg, corresponding to 30% of the mass in a typical KTX plasma; the CT velocity exceeds 120 km s⁻¹. It is observed for the first time that multiple CTs can be produced and emitted during a very short period (< 100 μs) in one discharge, which is significant for the future study of repetitive CT injection, even with an ultra-high frequency.