Study Of Start-up Plasma Character In EAST Based On Image Processing

In the EAST system, plasma discharge can be separate into four stages:(1) Ionization andavalanche,(2) current raises during low electron temperature,(3) current raises during moderateelectron temperature, and (4) plasma flat-top. This paper is mainly focused on the second stage,current raises during low electron temperature, when plasma just begins to breakdown. It isessential to properly control the plasma during this short period of time, because this is the mostcritical stage in the process of tokamak plasma discharge, and it is also the most importantdeterminant for the success rate of this process. During this period of time, since the plasmadoes not reach the equilibrium stage, the equilibrium theory cannot be applied. More importantly,in order to better characterize this stage, this paper presents a method which combines physicalmeans and probe assay,using image processing and simulation to study the start-up plasma.This way main include:(1) used a fast CCD image acquisition system to acquire images ofplasma discharge in the tokamak system.(2)Calculate the boundary of plasma, based on theimproved Otsu threshold’s canny algorithm, from the images of plasma discharge. In order todetermine the actual position of the plasma, the boundary data is filtered based on thecharacteristics of the plasma images, and plasma is best fitted by the least square method.(3) Thelabel data of EAST’s vacuum chamber region is calculated by using these calibrated images.Combined with the positional information of the plasma from these images, the actual position ofthe plasma in the EAST’s vacuum camber regions over-time can be calculated.(4)Using the measuring principle of single-turn loop and magnetic probe calculates both values and to make acomparison with actual data value. The most accurate and appropriate data value will be used forthe subsequent calculations.(5)Using eddy solving model and the center of plasma horizontaland vertical field solving model calculate them.(6)Make adjustments to both horizontal andvertical field in the plasma’s central region, and combine with tokamak’s circuit equation, toreverse-calculate the appropriate theoretical coil current.The method propose in this paper, not only to provide data for researchers to better controlplasma, but also according the requirements of researchers to add restrictions to get the data whichthey want.