Trials of RF plasma production using different antenna geometries with magnetic field

Abstract

Plasma production studies excited by the radio frequency (RF) wave were carried out using various antenna configurations. Six types of side antennae, located outside the large cylindrical chamber, and two types of internal loop antennae were tested. The ion saturation current I is of a probe and the plasma emission were measured as a function of the filling pressure, the RF power and the magnetic field. With the increase in the power and the magnetic field, I is increased in most cases, while some of the antennae showed the maximum I is values under low magnetic field. Among the side antennae, a spiral antenna produced the highest value of I is in a wide operational window. For the case of the internal loop antennae, the electric field parallel to the magnetic field did not show a significant contribution to plasma production. These results suggest the importance of the loop-like RF-induced electric field. When an external magnetic field was applied, the uniformity of the plasma produced by the internal loop antennae in both the radial and axial directions was improved.

Plasma control by modification of helicon wave propagation in low magnetic fields

“…The magnetic field present at the maximum of these density peaks has been shown experimentally 9 and numerically 12 to be approximately proportional to the wave frequency, and for frequencies of 13.56 MHz, occur at around 2-3 mT. 6,8,11 Associated with the density peaks of these low field helicons are corresponding peaks in the antenna loading resistance, 4,9,12 showing that the power transfer efficiency between the antenna and the plasma increases. Chen 4 has suggested that the formation of these peaks for m = 0 antennas is caused by constructive interference between forward waves launched by the antenna and reflected waves from an end plate.…”

“…2,4 At low magnetic fields ͑Ͻ10 mT͒, however, this proportionality no longer holds, and density peaks occurring over a narrow range of field values have been reported by several researchers. [5][6][7][8][9][10][11] These low field peaks have been studied over a fairly wide range of power and pressure values, with the large majority of work done making use of uniform magnetic field geometries. The magnetic field present at the maximum of these density peaks has been shown experimentally 9 and numerically 12 to be approximately proportional to the wave frequency, and for frequencies of 13.56 MHz, occur at around 2-3 mT.…”

Helicon discharges and sources: a review

“…A large helicon machine was built in Japan by Shinohara et al [74,75] It is shown in figure 27. Properties of the plasma have been studied with changes in the B-field uniformity and endplate conductivity [76], different types of antenna [77], including flat spirals tapped at various points and arrays of m = 0 loop antennas [78][79][80], and different sizes and aspect ratios of the discharge column, including diameters as small as 1 cm [81]. By biasing concentric-ring antennas, the radial electric field and plasma profile can be changed to study instabilities [82][83][84].…”

Discharge modes and wave structures using loop antennae in a helicon plasma source

“…Here, R c (0.4-0.5 ) and R p indicate the vacuum (i.e. circuit loss) and plasma loading resistances, respectively [39]. In this expression, the antenna loading (=P in divided by the square of the effective antenna current) is expressed as R p + R c (R c ) in the presence (absence) of the plasma, and the power coupling efficiency can be defined as R p /(R p + R c ).…”