Development and Performances Characterization of a Linear Mass Spectrometer for Diagnosis of High Energy Ion Beam

Vacuum is discharge, which is widely used in material surface modification, semiconductor doping and high-energy physics research in particle accelerator injection, the characteristics of vacuum arc discharge plasma, which are of great significance in practical application. Owing to characteristics of time-of-flight mass spectrometry (TOF), it is fast analysis, wide quality range and suitable for transient process, it has great advantage to availability of the information on the composition and charge distribution of the plasma. In our study，a linear time-of-flight mass spectrometer combined with vacuum arc ion source was developed using for diagnosis of high energy ion beam. The TOF analyzer mainly consisted of ion source, ion gate, lens system and MCP detector, the whole system was aligned coaxially with horizontal axis of the drift tube. Ions generated by vacuum arc discharge and accelerated by 30 kV DC high voltage were selectively passed through the ion-gate and then focused by lens system to reach the MCP detector. The effective distance of free-field flight region was 1.5 m. The mass resolution was higher than 90 FWHM by accurate intercepting of short-duration pulse ion gate，and the ion beam focusing effect was investigated by using ICCD high speed camera to improve sensitivity. The instrument could be used to analyze the ion compositions of plasma generated during discharge in various time. Rapid and accurate detection of plasma generated in the discharge process of vacuum arc discharge ion source was realized. Compositions of ionization in the initial stage of discharge (2 μs) were mainly gaseous ions, such as C⁺, O⁺, C²⁺ and O²⁺, and in the later stage of discharge (6 μs)，metal ion such as Fe⁺, Cu⁺ and their isotope peaks could be detected. At the same time, the information such as the species, charged state and relative content of ions produced by vacuum arc ion source discharge could be given, and the accurate diagnosis of the whole discharge process could be realized. Though this instrument was not yet able to achieve the quantitative analysis of the ionic components and the change of the plasma under different discharge voltages in this study, however, in similar studies, the research could be expanded on the basis of the results of the study, and carried out a more in-depth study of the vacuum arc discharge ionization performance by corresponding high-voltage and vacuum design and combining the actual ion source structure, such as the study of different acceleration voltages and different discharge voltages provide a new and reliable method for the research of vacuum arc discharge plasma in China, especially for high energy plasma detection.