Experimental Study Of Dynamo Effect In The Reversed Field Pinch Plasmas

Reversed field pinch is a toroidal magnetic confinement fusion configuration,and its confinement magnetic field is mainly produced by the plasma current.Its toroidal field and poloidal field are both of the same magnitude.The toroidal field decreases from the plasma core to the edge and reverses at the plasma edge.Reversed field pinch has significant advantages of simple engineering,high ? and ohmic heating directly reaching the ignition condition,so it is an important area for exploration of future mag-netic confinement fusion configuration.One of the most important phenomenon in reversed field pinch plasmas is the so-called dynamo effect.The plasma produces an ordered electric field,which drives the self generated current(self generated magnetic field),and the self generated magnetic filed in turn confines the plasma.Dynamo effect is the basic of the magnetic self-organization phenomenon and the key factor to under-stand the equilibrium and instability of reversed field pinch plasmas.Since reversed field pinch configuration has rich dynamo effects driven by a various of mechanisms,it's the best experimental platform for such problems.This thesis develops a multi-channel capacitive probe for electrostatic fluctuation measurement in the Madison Symmetric Torus(MST).Combined with the secondary electron emission technique,a capacitive probe can measure the plasma potential and a capacitive probe array can measure the electric field by the spatial differential of the plasma potentials.A multi-channel capacitive probe is used to measure the plasma potential and electric field at the edge of MST,and these equilibrium part and fluctu-ation part are obtained by the sawtooth crash event ensemble averaging method.The radial profile of the plasma potential,the plasma potential fluctuations and the elec-tric field fluctuations are analyzed during the dynamo effect.By analyzing the spectrum of the plasma potential fluctuations and the electric field fluctuations,the relationship between the tearing mode and the high-frequency turbulence is studied.By the saw-tooth crash event ensemble averaging of the tearing modes in MST,the amplitudes and phase velocities of the tearing modes during the dynamo effect are studied and the phase distributions of the tearing modes are given.This thesis uses the magnetic coils at the wall of MST to establish the eddy current probes,and uses the eddy current fluctuations to describe the localized characteristic of the dynamo effect in MST.Through statistical methods,the distribution characteristic of the time and the toroidal location of the dynamo effect in MST are analyzed.The wavenumbers and the group velocities of the localized wave packed during the dynamo effect are analyzed.By analyzing the time-space evolution of different quantities with respect to the dynamo time and toroidal location,the effects of dynamo effect on dif-ferent quantities are investigated and the radial localized structure of the dynamo effect is found.The eddy current fluctuations are used to analyze the localized characteristic of the dynamo effect,and then a deeper and clearer understanding of the dynamo effect mechanism is made.This thesis also develops a multi-channel capacitive probe for electrostatic fluc-tuation measurement in the Keda Torus eXperiment(KTX).A probe system is built in the horizontal port of KTX.The multi-channel capacitive probe is used to measure the plasma potential and the electric field in current different discharges of KTX.Spectral analysis and correlation analysis of these plasma potentials are made to try to find out the related plasma instabilities.Using the two-point method,the power spectral densi-ties of the plasma potentials in the radial,poloidal and toroidal directions are calculated and their propagation characteristics are studied.This thesis uses the non-uniform fast Fourier transform algorithm for mode analy?sis in KTX,since the edge magnetic coil array has a special design.By comparing with other MHD mode analysis methods that have been developed for many years,a set of mode analysis methods suitable for KTX is found out.In the current various plasma discharges of KTX,these methods are used for mode analysis,so the effectiveness and accuracy of these methods are compared to establish a set of mode analysis methods suitable for KTX.Attempts are made to use these methods to find plasma instabilities in the plasmas of KTX and to describe the mode characteristics of these instabilities.