Effect of external magnetic field on helix plasma plume

Abstract

<sec>Electric phenomena and magnetic phenomena are inseparable. The magnetic field affects the ionization balance and spatial distribution of the plasma. A new type of plasma discharges has been found in nitrogen gas under sub atmospheric pressure condition without external magnetic field. Because of its regular helical propagation pattern, it is called helical plasma (HP) plume. Although a great deal of research has been carried out on the key characteristics of the HP plume, the formation mechanism of it remains unclear, which affects its applications in materials and nanotechnology.</sec><sec>By applying magnetic field to HP with different chirality, the regulation behavior of the external magnetic field on HP is studied. It is found that the external magnetic field will make the HP shrink or stretch. With the magnetic field intensity increasing from 0 mT to 200 mT, the left-handed HP plume stretches under the magnetic field of S-pole. Conversely, the left-handed chiral HP plume contracts when the magnetic pole changes to N-pole. However, when the chirality of HP plume is changed to being right-handed by adjusting voltage, phenomenon opposite to the previous one is observed. Moreover, the applied magnetic field also affects the divergence of HP. With the increase of S-pole external magnetic field, the HP plume stretches until the external magnetic field reaches to 80 mT. When the magnetic field intensity is 80 mT, the HP disappears. The plasma in the quartz tube appears in the divergent form. With the magnetic field intensity increasing to 160 mT, the plasma in the form of a helix appears again. Finally, in the process of changing the intensity of the magnetic field, the clarity of the HP plume will also change.</sec><sec>The radial electric field of HP is calculated by electromagnetic wave theory, and the mechanism of the influence of external magnetic field on the behavior of HP is clarified. It is found that the magnetic field force component of Lorentz force is responsible for the external magnetic field regulating the HP behavior. This study lays a theoretical foundation for understanding the motion behavior of HP, which is conducive to the practical applications in the field of materials and nanotechnology.</sec>