Research Of The Impact Of ECRH On Edge Magnetic Island

Tearing mode is a common magnetohydrodynamic instability in tokamak devices,which is also one of the most harmful instabilities.Due to the effect of the tokamak vacuum vessel wall and the error field,the tearing mode may stop rotating and form a locked mode,which can reduce the confinement of the plasma and finally lead to disruption.Therefore,the measurement of the mode numbers,amplitude,phase and spatial distribution of the tearing mode has become an important subject for studying the MHD instabilities,and it is also the prerequisite for controlling the locked mode and avoiding disruption.In response to the above problems,this thesis uses multiple sets of magnetic probes to measure the locked modes and quasi-static modes on J-TEXT,which gives the basic information of the modes,such as amplitude and phase evolution.Besides,the Electron Cyclotron Resonance Heating(ECRH)system is used to suppress the boundary magnetic islands in this thesis.In this thesis,accurate measurements of the locked modes and quasi-static modes on JTEXT are carried out.First,the symmetry of the measurement signal of the new high field side(HFS)magnetic probe is analyzed,and the HFS magnetic probe array is used to make a preliminary measurement of the locked mode excited by the resonant magnetic perturbation field(RMP),which gives the time evolution of amplitude and phase.In addition,the signals measured by the toroidal magnetic probes and the ex-vessel saddle loops are additionally given,and the mode number of the locked mode,which is m = 2,is fitted according to the phase evolution measured by these three sets of signals and the poloidal angle of the magnetic probes.Besides,this thesis uses multiple sets of magnetic probes to measure the helical structure of the quasi-static mode in flux coordinate systematically.This thesis further explores the impact of ECRH on the boundary 3/1 locked island.First,the experimental results of 3/1 penetration under different RMP poloidal spectrum in high plamsa density situation are given.The method of measuring the amplitude and phase of the3/1 magnetic island using HFS probe array is discussed.It is found that the period and the amplitude of the sawtooth increases significantly after the ECRH depodited in the plasma core,which has a modulating effect on the amplitude of the 3/1 magnetic island.Each sawtooth collapse is accompanied by a decrease of the amplitude of the 3/1 magnetic island.The suppression has a threshold effect,and the time difference between sawtooth collapse and decrease of amplitude of magnetic island is 1 ms or so.Besides,the influence of the different ECRH power on the suppression of 3/1 magnetic island is also discussed.The results show that the suppression effect is better with higher ECRH power.The 400 k W ECRH can completely suppress the 3/1 magnetic island in low density situation.To solve the problem of locked mode disruption,this thesis uses multiple sets of magnetic probes on J-TEXT to measure the locked islands and uses ECRH to suppress the boundary 3/1locked island.The experiment results are highly repeatable,which have certain significance in suppressing locked mode for the future tokamak device.