The first plasma in a newly constructed linear device for plasma turbulence research

Abstract

Parameters of the first plasma in a newly built middle-size multi-functional linear plasma device named LEAD (Linear Experimental Advanced Device) were presented. The LEAD device is built to serve as a multi-purpose laboratory plasma experiment platform for various topics, including plasma turbulence, plasma-material interaction, and other fundamental plasma physics. This device is also useful for testing new diagnostic systems. It will be complementary to the HL-2A/HL-3 tokamaks in Southwestern Institute of Physics. The plasma was generated by a large-area helicon plasma source with a multi-ring antenna driven by a 13.56 MHz, 5 kW radio frequency (RF) power source. Argon plasma parameters were measured by a Langmuir probe in different external parameters including RF power, axial magnetic field, and neutral pressure. The threshold power for helicon mode transition is empirically confirmed to be 180 W. Steady-state argon plasma with a density of higher than 1019 m-3 was generated when RF power reached 3 kW. Plasma parameters are crucially influenced by the axial magnetic field. With a weak magnetic field, the radial density profile is Gaussian-like. However, with a stronger magnetic field, shear and reversion of azimuthal rotation velocity reversion appear, resulting in a hollow-shaped density profile. When further increasing the magnetic field, plasma density decreases. Steady-state plasma discharges were achieved under a wide range of argon neutral pressure from 0.1 Pa to over 10 Pa. With increasing neutral pressure, plasma density increases to its maximum at 2.5 Pa and then drops, while electron temperature drops monotonically.