Study The Properties Of Plasma Rotation Driven By Electrode Biasing On J-TEXT Tokamak

The plasma rotation of tokamaks plays an important role in the suppression of micro-turbulence and macro-magnetohydro(MHD)instabilities.Currently,many results about rotational physics have been achieved,however,there are still many problems(i.e.the driven mechanism of intrinsic rotation,the physical process of momentum transport,the effect of rotation onMHD instabilities and so on).Thus,study of the plasma rotation is still meaningful.In this dissertation,we bulid a retarding field analyzer(RFA),which is applicable to measure the ion temperature in the edge plasma of the J-TEXT tokamak.And we also optimize the electrode biasing(EB)system,which is applied to modify the plasma rotation.The experiments of this dissertation are as follows:Firstly,the ion temperature(Ti)profiles in the scrape-off layer(SOL)are measured by the RFA,and it is found that the Ti is 1.2-2.3 times of the electron temperature(Te,measured by Langmuir probes).Compared the Ti profiles under different configurations,it is found that the relation between the decay length(λT)of Ti and the magnetic connection length Lc approximately satisfies λT ∝(?);the Ti profile at the midplane of low field side is flatter than that of top side,showing poloidal asymmetric.It may be caused by the high cross-field transport at the midplane.Compared the RFA with Langmuir probes,the toroidal momentum balance in the EB source region is analyzed.The momentum damping coefficientμΦ is calculated as 103～104 s-1,furthermore,it is proved by experiments that the local toroidal momentum sink is mainly contributed by neutral damping.In addition,we developtheRFA application and realize the simultaneous measurement of Ti and Te.The single-probe principle is modified by this application and the rationality of the "cool ion"and "thin sheath" assumptions is proved.Secondly,toroidal momentum transport of J-TEXT plasma is studied based on the perturbation analysis method.Compare to the previous research,in this dissertation,the measurement of toroidal rotation profile is perfected and the modulated bias wave is optimized.According to the phase delay of modulated rotation,the time scale of momentum transport is determined,about 10 ms.The radial profile(r/a =0～0.82)of toroidal momentum diffusive coefficient(xΦ)and convective velocity(Vcon,v)are achieved:xΦ.in the range of 0～25 m/s,increasing with the radii;-Vconv in the range of 0～30 m/s,increasing with the radii but decreasing near the edge,and the results indicate the momentum transport coefficientsobviously outweigh the neoclassical prediction(-0.01 m2/s)and the convective velocity is always toward the plasma core,demonstrating the momentum pinch effect.Applying the momentum transport coefficients,the diffusion and convection of toroidal momentum are calculated.The diffusion is found to bean order of magnitude larger than the convection due to the momentum gradient an order of magnitude larger than the momentum,and the toroidal rotation profile is well reproduced by the recursion formula,which is derived from the momentum equilibrium equation.The effects of the momentum diffusion and convection on the rotation modulation are also analyzed.It shows the amplitude of modulated rotation is impacted by the convection and the modulated phase delay is mainly influenced by the diffusion.At last,the effect of EB on the 2/1 tearing mode is studied and the negative bias is used to try to unlock the locked mode.Statistic results display that positive/negative bias can drive plasma rotation in the co-/counter-IP direction,decelerate/accelerate the mode frequency,increase/decrease the poloidal perturbative magnetic field,and destabilize/stabilize the tearing mode.The variations of plasma rotation,mode frequency and poloidal perturbative magnetic field linearly depend on the bias voltage(current).The threshold voltages,which cause mode suppressed and locked,are found and impacted by the plasma parameters.Although the locked mode cannot be unlocked by the negative bias,the tearing mode is suppressed and locked mode is avoidedsuccessfully.This study show clearly that the EB with negative bias is able to drive the plasma rotation and suppress the tearing mode.It provides a new approach for avoiding locked mode and disruption.