The Effect of Magnetic Field and Pressure on the Threshold Power for Entering Helicon Wave Mode

Helicon wave discharges exhibit high coupling efficiency and can effectively generate high-density, high-ionization plasma. However, the radio frequency power, magnetic field, and pressure conditions for achieving wave coupled modes in helicon plasma are not the same. In this work, we used a right-helical antenna to study the effects of magnetic field and gas pressure on the threshold input power for entering helicon wave mode. The results indicate that within a wider range of magnetic fields (300-900 Gauss) and pressures (0.1-1.6 Pa), the threshold power does not change monotonically with the magnetic field strength, but shows a trend of increase-decrease. While the threshold power decreases with the increased pressure. At higher pressure (>0.8 Pa), the discharge is more likely to enter directly higher-order wave modes.