Research Of Influences Of External Resonant Magnetic Perturbations On Tearing Modes On The J-TEXT Tokamak

Tearing mode is a commonly existed instability in the tokamak plasmas, and its direct result is formation of the magnetic island. The transport in the magnetic island is very strong, which results in a large reduction of plasma temperature and density, consequently an aparent loss of confinement More serious is that if the magnetic island grows to a certain large level, it will cause damages of the magnetic surface structure and then major disruption. Investigating the tearing mode characteristics and finding practical control method is a key issue in future tokamaks and fusion reactors. Tearing mode carries magnetic perturbations with the same helicity as the equlibrium magnetic field line. An externally exerted magnetic perturbation with the same helicity is resonant with the tearing mode and may amplify or attenuate the perturbation. The attenuation of the perturbation indicates the suppression of the tearing mode and improvement of the plasma confinement. The interactions between the magnetic perturbation and the tearing mode are direct electromagnetic procedures and are fast, which makes the external magnetic perturbation is a promising method to control the tearing mode. However, how to make the external perturbation field decrease the tearing mode rather than amplifying it, the thorough understanding of the mechanism is required.To understand the mechanism of the interaction between the tearing mode and the perturbation field, and also to do some preliminary research about tearing mode control, a set of resonant magnetic perturbation (RMP) coils designed on the original TEXT-U tokamak is reconstructed on J-TEXT and now is named as SRMP. SRMP mainly produces m/n=2/1or3/1dominant resonant static perturbation. Because the tearing mode is always rotating in the plasma, a rotating RMP will interact with the tearing mode more intensively and is more flexible for tearing mode control. Basing on the mode structure of a single saddle coil and the properties of the Fourier Transform, a new set of RMP coils named as DRMP is designed and constructed. DRMP is installed inside the vacuum vessel and produces rotating or static2/1or1/1magnetic perturbations.A lot of RMP experiments have been carried out on the J-TEXT tokamak by using SRMP and DRMP. Mode locking, mode suppression and field penetration are all observed. The results indicate that the tearing mode with a low initial frequency can easily be locked by RMP, while a high frequency tearing mode can be suppressed obviously. Moreover, locked mode after mode suppression has been observed, which has been also found in the numerical simulation. The coincidence of the experimental results, numerical simulation and the analytic calculation verified the understanding of the mechanism of the interaction between RMP and the tearing mode, and also provide a foundation for future tearing mode control. The experiments and the analytic calculation carried out in this paper are the foundation of the tearing mode control.