The Experimental Study Of Filamentary Structure Transport In The Edge Of Tokamak Plasmas

Filamentary structures are widely observed in the edge and Scrape-off Layer(SOL) of tokamak plasma (mainly in bad curvature region). They are intermittent structures and typically have higher density and temperature than those of SOL. They also have large poloidal and radial scale lengths (A few millimeters to several centimeters). They extend along magnetic field line, and their correlation length along magnetic field line can reach dozens of meters. The life time of such structures range from dozens to sev-eral hundred of microseconds. They propagate in radial direction as well as in toroidal direction. And the radial propagation distance is several times larger than its radial scale length. It is generally acknowledged that filamentary structures are one of main contributors for the convective transport in edge and SOL regions. According to the generation mechanism, filamentary structures can be classified into two kinds:blob and ELM-filament.In this thesis work, Langmuir probe was used to measure the statistic of blob and ELM-filament, including their characteristics of typical scale, life time, poloidal and radial velocities. Two new methods were developed to extract filamentary structures, which are different from traditional method based on ion saturation. One method is based on floating potential, and the propagation of blobs and ELM-filaments in a10mm×12mm cross section were measured successfully by using a4×4probe array; The other uses the feature of filament radial velocity. Combining the data from a rake probe in poloidal direction, the ELM-filament2D potential and velocity profile can be reconstructed, in which charge polarization and bipolar velocity were observed.The ELM-filament mitigation, induced by supersonic molecular beam injection (SMBI) and pellet injection (PI) respectively, were also studied and compared. Though the two injection methods are quite different in many aspects, such as deposition po- sition, temperature, and the number of injected molecules etc, their effects on inter-mittent convective transport induced by ELM-filament are similar;1. The mitigation of larger amplitude filaments is observed. The burst rates of filaments whose density amplitude are larger than4σ(σ is the standard deviation of disturbance),decreased from～2.7kHz to～1.8kHz after SMBI and from～4.1kHz to～2.2kHz after PI;2. The mitigation of radial velocity was also observed in both cases. The average values decreased from～2.9km/s to～1.9km/s after SMBI and from～3.8km/s to～2.6km/s after PI, which might be caused by the E×B amplitude reduction. Statistical characteristics of filament radial velocity with density and potential struc-ture show that there are two terms contributing to the filament velocity (or potential structure) reduction:one is that the velocity decreases with filament density and the other is that the velocity decreases with filament temperature;3. The transient parti-cle and heat fluxes fall by more than50%in both cases due to the filament density and radial velocity mitigation;4.The reduction of filament correlation along magnetic field line (measured in divertor region and on the mid-plane) was also observed. And the electron-ion collisionality measured in divertor region is out of phase with this corre-lation, which implies that large scale structure on magnetic flux surface is suppressed due to filament parallel current. This process can be summarized as a simple phys-ical picture:"electron-ion collisionality↑(?) parallel plasma resistivity↑(?) parallel current↓(?) long-range correlation↓".Finally, chaos analysis method was introduced to the research of ELM control. The main result indicates that the burst of ELM is a chaotic process, and7Unstable Periodic Orbits (UPOs), which can be divided into two groups obviously, were found. It gives us a new method to study and control ELM.