Compact Tours (CT) injection is a highly promising technique for the central fueling of future reactor-grade fusion devices since it features extremely high injection velocity and relatively high plasma mass. Recently, a CT injector for the EAST tokamak, EAST-CTI, was developed and platform-tested. In the first round of experiments conducted with low parameter settings, the maximum velocity and mass of the CT plasma were 150 km·s−1 and 90 µg, respectively. However, the parameters obtained by the EAST-CTI were still very low and were far from the requirements of a device such as the EAST that has a strong magnetic field. In the future, we plan to solve the spark problem that the EAST-CTI currently encounters (that mainly hinders the further development of experiments) through engineering methods and use greater power to obtain a more stable and suitable CT plasma for EAST.

Compact torus (CT) injection is one of the most promising methods for the central fuelling of next-generation reactor-grade fusion devices due to its high density, high velocity, and self-contained magnetised structure. A newly compact torus injector (CTI) device in Keda Torus eXperiment (KTX), named KTX-CTI, was successfully developed and tested at the University of Science and Technology in China. In this study, first, we briefly introduce the basic principles and structure of KTX-CTI, and then, present an accurate circuit model that relies on nonlinear regression analysis (NRA) for studying the current waveform of the formation region. The current waveform, displacement, and velocity of CT plasma in the acceleration region are calculated using this NRA-based one-dimensional point model. The agreement between the model results and the experimental results is better than in the previous general model results estimated by the device dimensions in previous. The next-step upgrading reference scheme of the KTX-CTI device is preliminarily investigated using this NRA-based point model. This research can provide insights for the development of experiments and future upgrades of the device.

In this paper, a compact torus (CT) injector system is designed for experimental advanced superconducting tokamak (EAST). The injector system consists of a coaxial electrode and four pulsed power systems and generates self-organized CT with high density and velocity. In addition, the performance of EAST-CTI is evaluated using a series of diagnostics systems. The experimental results show that the velocity, electron density, and number of particles of the CT are 56.0 km/s, 8.73 × 1020 m-3, and 2.4 × 1018, respectively. The detailed description and experimental results are presented in this paper.

Compact torus injection (CTI) is a novel approach to fueling the core of a fusion reactor. In this paper, the force-free equilibrium based on the EAST-CTI is calculated. It is found that the α, which is proportional to the ratio of the toroidal current to the toroidal magnetic field, plays a key role for the force-free equilibrium. When it is smaller than the eigenvalue, the open poloidal magnetic flux decreases while the magnetic field strength increases as its value increases. However, once α equals the eigenvalue, the amplitude of the magnetic field tends to infinity and the boundary magnetic field is tangential to the wall. In addition, in this work we found that the eigenvalue is mainly determined by the width of the formation region, enlarging the width will significantly reduce the eigenvalue and further affecting the CT formation. Another interesting phenomenon in this work is that the poloidal magnetic field plays a hindering role in the formation of CT, and theoretically, CT is difficult to detach from the forming region when α'(α^'~J_p/B_p) is less than the threshold α_c. In experiments, we show that a discharge with α'<α_c leads to an increased delay between the onset of the current in the acceleration and formation regions. These findings provide some guidance for the carrying out of the experiments and future modifications of the device.