Preliminary analysis of back-streaming electrons on the source plasma region of ion sources for the EAST-NBI

Back-streaming electrons gain significant energy due to the high voltage of the extraction system for a high-current ion source.By theoretical calculation,the particle flux accounts for 13.88% of the total beam current,and the power flux accounts for about 7.5% of the total beam power.This shows that back-streaming electrons are very destructive to the plate of electron absorption that is installed opposite of the accelerator.At the same time,as particles impinge on grids,the energy level that the grids absorb will be really high.Compared with the water flow calorimetry data of ion sources on the ASIPP-NBI testbed,it can be found that,as the high voltage of the extraction system rises,the particle flux and the power flux of the back-streaming electrons are essentially in the same proportions.Therefore,the corresponding energy deposited on the components of the ion source will grow by the same percentage with the increase in high voltage,which demonstrates strong inhibition to improving the neutral beam power injected into a tokamak.