Novel technique for the extraction of ionization profiles from spatial density measurements

Abstract

A method has been devised to extract the two-dimensional ionization profiles from spatially resolved ion density measurements made in a capacitively coupled argon rf plasma. This technique is valid if the production process is ionization and the loss process is ambipolar diffusion. As this procedure calculates the total production (ionization) term, processes such as two-step ionization and photoionization are included. The main benefit of this new technique is that it extracts ionization rates that pertain to the total ionization in the discharge. It follows that this technique could be used to determine when other ionization processes (e.g., photo- and two-step ionization) are important. On testing with experimental data, the inversion process was observed to reproduce the original source term, thereby verifying that the iteration process converges to a real solution. The calculated ionization rate using the integral method is in good agreement with the ionization profiles obtained from the density measurements. Hence, there is now a method of determining the ionization rate that is independent of electron energy probability function measurement and that includes all ionization processes, not just ground state ionization by electron–neutral collisions.