Magnet Configuration and Experimental Analysis of Helicon Source for Space Magnetoplasma Propulsion

The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is one of the high performance electric propulsion devices for future interplanetary applications. Helicon sources can produce high-density plasmas with high-ionization efficiency suitable for VASIMR, which usually use two electromagnets to produce the required magnetic field configuration. How to optimal design the solenoids and how to create the requisite B-field are the key factors to affect the characteristics and performance of the helicon plasma. In this paper, the magnets were designed and fabricated, and an experimental helicon source was presented. Two solenoids situated around the cylindrical quartz tube were used to create an expanding magnetic field of about 250 G in the center decreasing to a few tens of Gauss in the downstream diffusion region. The antenna was powered by a radio-frequency (RF) system of 13.56 MHz, which maximum changeable power is 500 W. Our helicon device was installed with vacuum chamber that is pumped down to a base pressure of about 0.001 Pa using cryopumps. Langmuir probe is mounted on to measure the plasma parameters. It is found that, when increasing the radio-frequency power or varying the magnetic field, both the plasma density and operating mode of helicon-wave ion are also changed. Permanent magnets (PM) and High temperature superconducting (HTS) magnets are also considered to use in the helicon source, and relative analyses are discussed. The details of further research are to investigate the relationship that the applied magnets affect on the efficiency and performance of the helicon plasma.