Characteristics of inductively coupled plasma (ICP) and helicon plasma in a single-loop antenna

Large area uniform plasma sources, such as high-density magnetized inductively coupled plasma (ICP) and helicon plasma, have broad applications in industry. A comprehensive comparison of ICP and helicon plasma, excited by a single-loop antenna, is presented in this paper from the perspectives of mode transition, hysteresis behavior, and density distribution. The E-H mode transition in ICP and the E-H-W mode transition in helicon plasma are clearly observed in the experiments. Besides, the considerable variation of hysteresis behavior from inverse hysteresis to normal hysteresis by the influence of the magnetic field is explored. The bi-Maxwellian and Maxwellian electron energy distribution functions in each discharge are used to explain this phenomenon, which is essentially related to the transition from a nonlocal kinetic property to a local kinetic property of electrons. In addition, we notice that the plasma density, in the radial direction, is peaked in the center of the tube in ICP, but a complicated distribution is formed in helicon plasma. In the axial direction, the maximum plasma density is still in the center of the antenna in ICP, whereas the highest plasma density is located downstream, far away from the antenna, in helicon plasma. It is believed that the reflected electrons in the sheath and pre-sheath by the upper metallic endplate and downstream propagated helicon wave will be responsible for this plasma density profile in helicon plasma. Due to the constrained electron motion in the magnetic field, an extremely uniform density distribution will be obtained with an appropriate axial magnetic field in the wave discharge mode.