احسان برنوسي

This research provides a comprehensive an‎d systematic investigation of the effect of magnetic field intensity in a divergent configuration on the characteristics of direct current (DC) electrical discharge under high vacuum conditions (less than 10−3 mbar). Creating an‎d sustaining plasma at such low pressures is a significant challenge due to the drastic reduction in the probability of ionizing collisions. Aiming to fill the existing information gap in this field, this study utilizes two complementary approaches: computer simulation an‎d experimental investigation. In the simulation section, a filament cathode plasma source with an external magnetic circuit was modeled using COMSOL Multiphysics software. In this model, the distribution of electric an‎d magnetic fields was calculated, an‎d subsequently, the trajectory of electrons was analyzed using the charged particle tracing module. The simulation results indicated that the divergent magnetic field configuration effectively confines electrons, an‎d as the field intensity increases, their residence time in the discharge region is prolonged, leading to a significant improvement in ionization efficiency. In the experimental section, a modular an‎d custom-built plasma source, capable of varying the number of permanent magnets (to adjust field intensity), was designed an‎d constructed. This source was installed inside a high-vacuum deposition system (IONEX), an‎d the plasmaʹs voltage-current (V-I) characteristics were recorded under the influence of three key parameters: gas pressure (regulated by a precision needle valve), filament current (controlling the emission of primary electrons), an‎d magnetic field intensity (in three configurations: weak, medium, an‎d strong with 3, 6, an‎d 12 magnet columns, respectively). The experimental results showed that the filament current, as the source of primary electrons, has the most potent influence on the plasma currentʹs magnitude. Increasing the gas pressure reduces the breakdown voltage an‎d increases the current density. Most importantly, the results clearly demonstrated that increasing the magnetic field intensity significantly enhances the discharge efficiency, enabling the system to produce a stable plasma with substantially higher current density at much lower working pressures. This research successfully demonstrated that by simultaneously controlling these three parameters, the plasma characteristics can be precisely tuned over a wide operational space, thereby overcoming the challenges of electrical discharge in a high vacuum.

تخليه الكتريكي , پلاسما , خلأ بالا , ميدان مغناطيسي

Electrical Discharge , Plasma , High Vacuum , Magnetic Field

Ehsan Bernosi

Mostafa Salahshoor