Study On Electron Drift Injection And Low Loop Voltage Start-up In J-TEXT

Plasma breakdown is a necessary step for successful plasma start-up and current formation in a tokamak.In order to initiate breakdown in tokamaks,a few requirements have to be satisfied.To date,due to restrictions in the free electron population and original magnetic flux(volt-second),and the adjustment range of poloidal field null geometry and prefill gas pressure,several RF(radio frequency)assisted approaches such as electron c-yclotron radio frequency(ECRF),low-hybrid radio frequency(LHRF),and ion cyc-lotron radio frequency(ICRF)have been applied to accomplish effective pre-ionization.But these complex and expensive RF assisted systems are unsuitable for smallscale conventional tokamaks.Consequently,development of a flexible and inexpensive method for reliable and effective breakdown is desirable.Electron drift injection is an innovative method.An external electric field E is applied outside the plasma region in the direction perpendicular to the toroidal magnetic field,which enables the electron beam emitted from the hot cathode to have a drift velocity E×B/B~2 directed at the origin of the plasma minor radius.To be brief,Electron emitted by the hot cathode undergo the E×B drift in order to traverse the magnetic field.In this paper,The electron drift injection system on the Joint Texas EXperiment Tokamak(J-TEXT),which includes injector system,hot cathode,vacuum system,power system and control and acquisition system,is designed and constructed.On this foundation,a series of experiments have been conducted.Finally,low loop voltage start-up with E×B drift electron injection is successful.Furthermore,the breakdown delay is reduced.Through experiments,it is demonstrated that the concept of electron drift injection is feasible and effective.