Study On Plasma Parameter Diagnosis Of Pulse Vacuum Arc Ion Source

Vacuum arc ion source is a kind of source which used to produce metal or mixed metal-gas ion beams. It has a compact structure, and provides large ion beam in low pressure. The source is mainly used in material surface modification of ion implantation and ion beam injector of particle accelerator. This kind of ion source first appeared in the1940s, after the tireless efforts of the researchers, vacuum arc discharge theory and corresponding experiment diagnosis Obtained many achievements. In order to obtain a better quality ion source, the researchers made a lot of diagnosis on the plasma produced by vacuum arc discharge. Throughout these diagnostic work, most of them were aimed at vacuum arc ion source which pulse width were hundreds of microseconds or millisecond level. There were few people study on microseconds level discharge of vacuum arc ion source.In this paper, the plasma produced by microsecond level discharge of vacuum arc ion source which developed by ourselves was diagnosed. According to the position of the plasma, adopted three kinds of methods to study the electron density and electron temperature of plasma parameters and so on. Titanium cathode and stainless steel anode were used in the experiment. The discharge pulse width was set to5μs around.The electrostatic probe method was used to study plasma parameters in the expansion cup. According to the principle of single probe diagnosis, a large bias tablet was used to obtain the ion flux and arc voltage along with the change of arc current; Making a small single probe work in saturation ion area to obtain the spatial distribution of the plasma inside the expansion cup; According to the principle of double probe diagnosis, the plasma electron temperature and electron density in the expansion cup were measured. The experimental results showed that the ion flux and arc voltage increase with the arc current; Plasma density along the axial direction decreased with increasing distance, and the density distribution was not uniform along the radial direction; Within80A to120A arc current, electron temperature was about3eV to5.5eV, the electron density of5.5×1012cm-12to9.5×1012cm-12n. They were increased with the arc current.The emission spectrometry method was used to study plasma parameters between anode and cathode. Emission spectroscopy diagnosis platform was established. The emission spectrum of plasma produced by the ion source worked with60-100A were measured. The experimental results showed that the plasma in this region was far from thermal equilibrium, an electron excitation temperature was about0.5eV, electron density was about1015cm-3 level. Both of them were tended to increase with arc current.The freezing model was used to calculation the frozen plasma electron temperature and electron density. Lacking of the ion source mass spectrometry data, the CSD of titanium cathode vacuum arc discharge data which measured by I. G. Brown, A. Anders and so on were used to calculation. The electron temperature of freezing zone was about2.8eV to4.4eV. The Order of magnitude of electron density was1018cm-3to1020cm’3. The calculation showed that the mean ion charge state decreased with increasing particle density and increased with the electron temperature.The above results has positive significance to understanding the microsecond vacuum arc discharge process, also provides plasma parameters to assess the ion source performance.