Experimental study of charge composition of diffuse vacuum arc in axial magnetic field by optical spectra

One of the issues of plasma technologies is the design of a high-performance plasma source. Due to its properties, a diffuse vacuum arc discharge may be one of the promising options. In this study, the dependence of the charge composition of a diffuse vacuum arc plasma with a hot cathode on the value of the external axial magnetic field and discharge voltage was investigated. The study was conducted with a thermionic gadolinium (Gd) cathode. Monitoring the charge composition was done by analyzing the emission spectra of the plasma. Steady states of arc discharge were obtained for a range of parameters. The arc currents were 30 and 40 A, the arc voltage was up to 29 V and the external magnetic field was varied from 0 to 20 mT. It was found that in the presence of the eternal magnetic field the defining factor of the charge composition was the arc voltage. Moreover, for a fixed arc voltage, an increase in magnitude causes an increase in intensities of all atomic and ionic plasma components (Gd, Gd⁺, Gd⁺⁺). The potential causes of this effect were discussed. It was established that in an axial magnetic field it is possible to implement discharge modes with predominance of single-charge ions by increasing the magnitude of the external magnetic field. Potentially, these discharge modes will be of use for the implementation of plasma methods for reprocessing spent nuclear fuel.