Experimental Study Of Supersonic Molecular Beam Injection On J-TEXT Tokamak

In order to realize the self-sustained controlled fusion, tokamak plasma needs to satisfy the energy triple product condition. To achieve the required plasma density, economic fuelling methods with fast response and high efficiency are necessary. Traditional gas puffing has a low efficiency and long response time, which cannot meet the demand of future fusion devices. Therefore, it is very urgent to explore new fuelling methods. Supersonic Molecular Beam Injection (SMBI), with high fuelling efficiency, simple construction and extensive applications, has been widely used in different magnetic confinement devices. Much progress has been made. Figuring out the SMBI penetration process and the mechanism of its interaction with plasma, and combining with the existing fuelling methods to provide an efficient solution for tokamak or even fusion reactor, are some problems needed to be solved in the current research. Except for fuelling, SMBI is also developed for other different physics research such as particle transport, ELM control, non-local electron heat transport and density feedback, etc. It becomes a good perturbation source for edge plasma. The major contents of this thesis are the design and installation of SMBI system for J-TEXT tokamak, and the related studies of plasma fuelling and nonlocal transoport.The thesis investigates the formation principle of SMBI, introduces the development in the various devices. On the basis of past experience, a SMBI system has been designed and installed on the J-TEXT tokamak. The system has two subsystems, namely HSMBI and LSMBI. Besides the traditional vertical injection and normal temperature injection, the systeme can realize angular injection and cryogenic injection. The thesis introduces the system component such as gas line, injectors and controller, and gives the test results.By comparing the SMBI fueling performance under different injection parameters (such as pressure, pulse width), the thesis investigates the effect of injection amount. The experiments find that SMBs with different injection amount have differnent fueling performance, which mainly includes two cases:moderate SMBI and intensive SMBI. The difference is that whether the SMBI triggering magnetohydrodynamics (MHD) instabilities. With the moderate SMBI, MHD instabilities are not triggered, the injected gas can promptly increase the density with a large margin, with a maximum fueling efficiency of50%. During the intensive SMBI, MHD instabilities are triggered, and plasma confinement degrades. SMBI fueling performance suffers, with an efficiency of10%-25%. The thesis studies the relationship between fueling efficiency and plasma parameters, and disscusses the optimized solution of SMBI fueling.The thesis analyses the SMBI penetration process and the plasma behavior. The averaged beam velocity is estimated, as well as the observation of deposition location. The results show that the SMBI mainly deposits about1-2cm inside the LCFS, the maximum depth reaches4cm. The thesis tells the evolution of temperature, radiation, rotation, turbulence during SMBI. The results of moderate SMBI show that, a certain degree of current density peaking is helpful to improve the plasma confinement, which the fluctuation of ion saturation current and floating potential significantly decreases. While in the case of intensive SMBI, the exceedingly peaked current density often leads to the triggering of2/1tearing modes.In the low desitiy regime of J-TEXT discharges, the nonlocal eletron heat transport phenomenon is successfully observed by SMBI. On J-TEXT, the core temperature generally increases with10-15%, and maintains for more than ten milliseconds, which is comparable with the confinement time of J-TEXT. By changing the qa, the experiments find that the location of inversed temperature is between q=1and q=2. For J-TEXT ohmic discharges, the critical value is about1.7×1019m-3. Besides, the effect is enhanced when the resonant magnetic perturbation is applied at the same time. With the present experiment results and theory, the thesis discusses the mechanism of nonlocal effect.