Characterization of Plasma Discharge in a Multi Dipole Line Cusp Magnetic Field Created by an RF Source Coupled by a Spiral Antenna

A detailed characterization of RF–plasma discharge in the multi-cusp plasma device (MPD) having a multi-dipole line cusp magnetic field (MMF:
$B_{0}$
) has been experimentally demonstrated using the externally employed four turns high power spiral antenna. The experimentally measured input impedance (
$\sim $
0.37 +
$\text{j}80\,\Omega$
) of the complete antenna system along with the MPD is found to be in good validation with the CST–MWS simulated result (
$\sim $
0.3 +
$\text{j}88\,\Omega$
). The cusp magnetic field (
$B_{0}$
) along the MPD chamber is also validated and has a good agreement with the simulated results for the magnet current of
$\sim $
150 A. The antenna is then made to resonate at 13.56 MHz using an external L-type matching network (MN) along with an RF source. It is found that the plasma density shifts to a maximum (
$n_{e} \sim 3.2 \times 10^{17}/\text{m}^{3})$
value at the argon-filled pressure of
$2\times 10^{-3}$
mbar for large
$B_{0}$
and RF power of 1 kW. Further, the input resistances of the antenna with a vacuum (
$R_{v} \sim 0.27\,\Omega$
) and plasma (
$R_{p} \sim 0.55\,\Omega$
) inside the MPD under the matched condition are also measured experimentally using the Rogowski coil. This concluded that the RF power coupling efficiency (
$\eta$
) with the Argon plasma is
$\sim $
68%. A plasma with nearly a uniform density of
$\sim 2.7\,\times \, 10 ^{17}/\text{m}^{3}$
is obtained up to a radial distance of
$\sim $
5 cm from the MPD center at the constant RF power of 800 W for the Argon-filled pressure and magnet current of
$4\times 10^{-3}$
mbar and 100 A respectively.