The effect of radial inhomogeneity on the collisional power absorption in helicon plasma sources

Abstract

The paper reports on the effects of plasma radial inhomogeneity on the power absorption in a helicon plasma source, which are computationally investigated by the CST Microwave Studio code. RF (13.56 MHz) power deposition was studied using three designs of antennas, namely, the Nagoya type-III, the fractional helix, and the single loop. Argon was used as the plasma working gas at the operating pressure of 15 mTorr. We have focused on the collisional power absorption utilizing WKB approximation to describe the plasma inhomogeneity. The obtained results show that the radial inhomogeneity has different effects on the power absorption at the low and the high magnetic fields. It is found that at low magnetic fields (i.e., B0=0.01 T), there is a specific density (nc) ranging from 5×1018 m−3 to 1×1019 m−3, before and after which the radial inhomogeneity decreases and increases the absorbed power, respectively. On the other hand, at high magnetic fields (i.e., B0=0.1 T), the inhomogeneity has no regular effect on the power absorption in various plasma densities. In addition, for a given plasma density (e.g., n=1018 m−3), as the magnetic field increases, the radial inhomogeneity effect on the power absorption would decrease for the Nagoya type-III and the fractional helix designs. However, for the single loop antenna design, this effect is negligible.

Coupling of RF antennas to large volume helicon plasma

“…Therefore, for low-density plasma, parabolic density profile is better than Gaussian density profile in terms of coupling efficiency, whereas for high-density plasma the latter is better. The variation profile of power absorption with Gaussian plasma density resembles the result obtained by others [31].…”

“…Overall, the relative power absorption for parabolic density profile is much bigger than that for Gaussian density profile, and the loop antenna results in higher relative power absorption than the other three antennas. This superiority of loop antenna was also observed before [31].…”

“…Overall, the relative power absorption for parabolic density profile is much bigger than that for Gaussian density profile, and the loop antenna results in higher relative power absorption than the other three antennas. This superiority of loop antenna was also observed before [31]. Figure 3 shows the stream plots of perpendicular wave magnetic field, wave electric field and perturbed current for half helix antenna and loop antenna, together with their comparisons in terms of magnitude.…”

The effect of Landau damping on the power absorption in a helicon plasma source driven by an m = 0 antenna

“…Note that the electron–neutral collision frequency is proportional to the electron temperature ( ν en ∝ T e ), whereas electron–ion collision frequency has an inverse affinity () . On the other hand, ν ei also increases with increasing electron density.…”

“…In spite of many 1D and 2D ( r , z ) models presented for wave propagation and absorption simulation in helicon plasma sources, , , only a few 3D simulations have been carried out . In our previous work, the effects of the plasma parameters on the collisional power absorption were investigated using the CST 3D simulation code . However, since collisionless power absorption is one of the main mechanisms in the helicon plasma source, the purpose of this investigation is to determine the effect of Landau damping on the power absorption by numerical calculation and simulation.…”