Development of A Compact High-Density Blue-Core Helicon Plasma Device under Strong Magnetic Field of Ring Permanent Magnet

Due to the high density and high ionization rate of helicon plasma, there is a keen interest in the application of helicon plasma, and efforts as been done to broaden their operatable parameter range, particularly with miniaturization of such devices [1,2]. Helicon plasmas are commonly generated in a cavity with a relatively large diameter or a relatively long plasma length[1], this comes from the consideration of the dispersion relation of the helicon waves and the basic consideration that the cavity length of the device is generally longer than at least one wavelength of helicon wave in order for helicon waves to be excited. But, in this paper, a bule-core helicon plasma device, seemingly more compact than allowed by the helicon dispersion relation, has been developed. The construction of this apparatus along with the experimental results are described. We have successfully produced high-density blue-core plasma using quartz tubes with small diameters of 26mm and length of 40cm, with the effective length of the plasma further limited by the magnetic fields of the permenant magnets. Blue-core transition is preliminarily found possible with a radio frequency power ~580 W and RF frequency 13.56 MHz, under the magnetic field strength ~2kG generated by a set of ring permanent magnet with a length of 20.8cm, in low pressure less than 1 Pa.