| Vacuum arc discharge could produce almost all of the metal ions with high charge states,and the extracted ion beam’s currents are strong,so they are utilized widely in many application fields,such as film deposition,ion implantation,ion accelerator.Specially,deuterated cathode could replace metal cathode in the vacuum arc discharge to produce strong deuterium ion beam.These devices are widely adopted in the sealed neutron tubes,which are used in the well logging,neutron activation analysis,and nondestructive examination.Although vacuum arc discharge is used widely in the industries,and it is researched over more than a hundred years,it is still unclear about its exact process.Many researchers studied mainly on the metal cathode,and the deuterated cathode is studied less.Comparing with the metal cathode,there are two more progress for the deuterated cathode,which are deuterium release and ionization.So the vacuum arc discharge with deuterated cathode is more complicated.This paper focuses on the vacuum arc discharge with deuterated cathode,employs electronics and optics diagnoses,and experimentally measures many characteristics,such as cathode spot,deuterium release,plasma parameters and deuterium ion’s ratio in the plasma.Cathode spot is the most famous characteristic of vacuum arc.This paper employs ICCD camera and SEM microscope to observe cathode spot caused by vacuum arc discharge with deuterated cathode.In order to photograph a clear and big image,a set of enlarged lens are produced.The smallest time resolution of ICCD camera is 2 ns,less than cathode spot lifetime,so the temporal process could be recorded.The results show that the new cathode spots are generated just nearby the old ones,which is caused by the deuterium gas beyond cathode surface.So the cathode spots are gathering together,and emit a big luminous spot.Sometimes,there are two or more luminous spots due to the droplet far away from the exited cathode spots.The angular distributions of different particles are measured by narrow band filter,and the results show that the deuterium atoms are more uniformity,while the Ti ions are concentrated around the cathode spots.The SEM results show that the craters are neighbour,which is coincided with photograph’s results.And the craters are the first type of cathode spot.There are many porous in the craters left by deuterium release,which make the surface looked like flocculence.Deuterium release is the unique characteristic of vacuum arc discharge with deuterated cathode.This paper firstly employs an airtight cavity to measure the deuterium quantity,which is about 1013 molecules when arc current is about some tens of amperes.And then,this paper employs element trace method to measure the residual deuterium beyond the cathode surface,which is about 0.1 Pa and easy to saturate at the later stage of discharge affected by the continuous distribution of cathode spots.Plasma parameters are important characteristics of discharge,which mainly include electron temperature and density.During the vacuum arc discharge with deuterated cathode,deuterium participates in the process of collision and ionization,and affects the plasma parameters badly.This paper employs optical emission spectroscopy to analyze the plasma spectra.And the results show that the electron temperature is about 1 eV,and the electron density is about 1015cm-3.Deuterium ion ratio is a special parameter payed close attention by ion source,which affects the efficiency of the extracted beam.This paper produces a simple magnetic analysis device just to distinguish gas and metal ions.This device could measure the deuterium ratio in the plasma conveniently.Because titanium atoms are more easily ionized and reflected in the cathode sheath,the deuterium ion ratio in the plasma is about 30%,lower than that in the electrode.This paper experimentally research the vacuum arc discharge with deuterated cathode,and the results are helpful to understand the discharge process and introduce the ion source design. |
