Experimental Investigation On The Interaction Between Edge Density And Radio-frequency Wave

Radio frequency (RF) wave heating and current drive are crucially important for steady-state high-confinement operation in the Tokamak. The RF wave interacts with edge plasma before driving plasma current or heating plasma. The lower hybrid wave is highly sensitive to the edge plasma density, and both the edge density and its fluctuation can affect LH W-plasma coupling and current drive. Therefore, investigation of the interaction between the RF wave and edge density and its fluctuation to improve RF wave heating and current driving ability is of great significance. This thesis carries out experimental research and simulation analysis on the effect of the low hybrid wave and the ion cyclotron wave on edge density based on measurements with low hybrid wave launcher probes. The main contents are as follows:1) The top and bottom probe were installed on the 4.6GHz LH launcher in order to study the density profiles in the vicinity of the launcher under different conditions(magnetic field direction and low hybrid wave power), and we found the decisive factors causing uneven density profiles and asymmetry in the poloidal direction. Based on the measurements of the 2.45GHz and 4.6GHz launcher probes and visible camera images, we compared the density profiles around the two LH launchers, and performed analysis and simulation. The results showed that an E x B convection effect resulting from the low hybrid wave power could influence the transfusion process of density at the front of the launcher, and brought about unevenness of density distribution and asymmetry in the poloidal direction. The thesis further analyzed the influence of the poloidal component and radial component of E x B, undisturbed plasma potential,neutral gas ionization and other factors on density distribution. It was discovered from simulation that the decisive factor causing the above density distribution was the radial component of E x B, and the radial convection directions are opposite at each waveguide center, which resulted in the "peak" and "valley" of density profiles, and the"peak" of density deviated from the waveguide center. The poloidal component of E x B and undisturbed plasma potential could not decisively influence the density distribution, but only modify the density distribution caused by the radial component of E × B. The density at the front of the launcher wholly increased when the effects of ionization of neutral gas were included. The density of the top and bottom probe increased or decreased with increase of power, but the trend was not equal, so that the simulation results were much closer to the measured results.2) Statistical and coherence analysis of ion saturated current of probe and reflection coefficient of low hybrid waves were conducted to study the impact of H mode discharge on the LHW-plasma coupling. The research showed that density fluctuation had an inverse relationship with reflection coefficient in the third standardized moment. It was discovered from coherence analysis of ion saturated current that the reason why LHW-plasma coupling difference was caused by different ELM forms was that density around the LH launcher increased more at unit time resulting from low-frequency, large-amplitude ELMs. So LHW-plasma coupling with low-frequency, large-amplitude ELMs was better than that with high-frequency, small-amplitude ELMs and with no ELMs. These analyses provide an important basis and data support for previous experiments.3) This thesis firstly studies suppression of intermittent structures (or "blobs")by the ion cyclotron resonance heating (ICRF) on EAST through statistical analysis and coherence analysis of ion saturated current. The threshold power of two ICRF launchers to suppress blobs was also given. The blobs structures in the region magnetically connected to the I port ICRF launcher can be fully suppressed with a threshold ICRF power below 0.5MW, and the fluctuation level deceases by 45% when the ICRF power is switched on; the probability density function (PDF) of ion saturated current was close to Gaussian distribution. For the regions that are not magnetically connected to the B port ICRF launcher, the suppression effects still exist, however, a higher ICRF power greater than 1.0MW is required; the fluctuation level deceases by 12-30 % depending on the ICRF power in the range 0.5-1.0MW, and the PDF of ion saturated current moved gradually to Gaussian distribution. E x B shear flow was probably the reason for the suppression of the "blobs".