The Three-dimensional Equilibrium Simulation And Preliminary Experimental Study In KTX Reversed Field Pinch

The three-dimensional(3D)effect has attracted increasing attention in toroidal magnetic confinement fusion devices because of the development of plasma parameters recently.In reversed field pinch(RFP)device,3D quasi-single helicity(QSH)states can improve the confinement of plasma greatly.The realization and control of QSH states need further reasearch.This paper simulates the 3D magnetohydrodynamic(MHD)equilibrium in Keda Torus eXperiment(KTX)RFP device.The electrostatic dynamo effect in QSH states is studied then.The confinement characteristics of collisionless particles in magnetic configuration are provided.The 3D equilibrium reconstruction of KTX is realized,and the preliminary experimental study of QSH states on KTX is carried out.Firstly,this paper simulates the 3D MHD equilibrium,which is based on the KTX geometry and design parameters.The equilibrium magnetic field and current density profiles of KTX are obtained by using VMEC code.The accuracy of the equilibrium simulation is verified by the instability analysis.The QSH states equilibrium of high current operation on KTX is simulated.The QSH state is compared with multiple helicity(MH)states to summary the equilibrium characteristics of KTX.Secondly,this paper study the mechanism of electrostatic dynamo effect in sustaining helical plasma equilibrium.The assumption of quais steady-state magnetic field is considered and the time-varying current dencity is overlooked.The electrostatic potential and electrostatic drift can be computed by the 3D equilibrium magnetic field and Ohm’s law then.It is found that the electrostatic potential is bipolar and is comparable with the terms of Ohm’s law.The electrostatic drift of QSH states almost dominates the plasma drift and dynamo velocity field.It is verified that the electrostatic dynamo effect plays an important role in generating and sustaining the helical states in RFP.Thirdly,this paper study the confinement of 3D magnetic configuration on radial drift particles.In steady-state magnetic configuration,the guiding center drift motion in Boozer coordinate is simplified by the initial conditions for particles.The 3D drift velocity in the magnetic field is computed then.The improvement of particle confinement is analyzed by 2D expansion of drift velocity on the magnetic surface.It is found that the increasing of poloidal and toroidal drift velocities can contribute to the improvement of particle confinement in QSH states.The 3D orbit of the particle can be plotted by the 3D drift velocity.It shows that the enhancement of radial drift velocity may lead to the deterioration of MH particle confinement.It is an effective method to reduce the radial drift velocity by reducing the amplitude of the secondary helical mode of magnetic field,which can improve particle confinement.Finally,this paper realizes the 3D equilibrium reconstruction on KTX,and carries on the preliminary experimental study in the QSH state.The V3FIT code uses VMEC as the equilibrium solver and implements magnetic diagnostics and interferometer diagnostics to do the equilibrium reconstruction on KTX.To satisfy the experimental observation of QSH states,the soft X-ray tomographic system on KTX is designed by using Bayesian experimental design.The signal simulation of polarization/interferometer diagnostics in MH and QSH states is provided to study the evolution and difference of the two states.