Characterization of a new variable magnetic field linear plasma device

Abstract

A radio frequency plasma device is presented in which the regions of plasma creation and maximum plasma magnetization can be separated along a 1.5-m tube. Measurements of the plasma density, plasma potential, and electron temperature in the device successfully reproduce previously reported plasma features. These validate the ability of the experiment to continue the investigation of a regime of operation in which the axial plasma density follows the profile of the applied magnetic field, as long as the ions are magnetized under the antenna. The density is shown to increase on axis owing to the decreasing cross section of the converging magnetic funnel connecting the antenna region to the solenoids. When the funnel pinching is increased, stronger magnetic fields are required to inhibit cross-field diffusion and to bring the density on axis in the expected 1012 cm−3 range. Collisionless transport of hot electron populations is observed along the field lines which intersect the area under the antenna and coincides with the presence of high-density conics more than 0.5 m away from the antenna for magnetic fields ≥600 G.

Helicon waves in a converging-diverging magnetoplasma

“…using a single-loop antenna at 27.12 MHz. While the new experiment closely reproduced the plasma parameters obtained in the former [28], rf magnetic waves identified as m = 0 helicon modes were detected with the B-dot probe. These measurements are presented and characterised here.…”

Data Processing Techniques for Ion and Electron Energy Distribution Functions

“…The data used in this study has been acquired using Moa 31 , a radio-frequency plasma reactor that is an expansion of Huia 32,33 . It consists of a 150 cm long, 9 cm inner diameter borosilicate glass tube plasma source connected to a 70 cm long, 50 cm diameter steel expansion chamber hosting the pumping system and the pressure gauges.…”

“…11 for more details). For this purpose a grounded aluminium sleeve of adequate surface area was inserted inside the dielectric plasma source tube at the end opposite to the diffusion chamber 32 . With the loop antenna capacitive coupling to the plasma, oscillations of the plasma potential at the applied radio-frequency and its harmonics are known to cause severe distortions to LP I-V characteristics 11,37 .…”

“…The Langmuir probe is mounted on a movable doglegged eccentric dielectric shaft which can span the entire length of the plasma source tube 32 . The RFEA is mounted on a movable (rotation and translation) 6.35 mm diameter steel shaft introduced in the top port of the expansion chamber, with the probe orifice facing the plasma source exit to detect any possible directional ion beam.…”

“…5. tions create an inductively coupled plasma exhibiting a symmetrical single peaked axial plasma density gradient ranging from 10 12 cm −3 under the solenoids to 10 10 cm −3 at the extremities of the glass tube 32,33,53 . The LP was placed on axis halfway between the antenna and the solenoids.…”