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

A method has been devised to extract the two-dimensional ionization profile s from spatially resolved ion density measurements made in a capacitively c oupled argon rf plasma. This technique is valid if the production process i s ionization and the loss process is ambipolar diffusion. As this procedure calculates the total production (ionization) term, processes such as two-s tep ionization and photoionization are included. The main benefit of this n ew 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 ion ization) are important. On testing with experimental data, the inversion pr ocess was observed to reproduce the original source term, thereby verifying that the iteration process converges to a real solution. The calculated io nization rate using the integral method is in good agreement with the ioniz ation 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 p rocesses, not just ground state ionization by electron-neutral collisions. (C) 2001 American Institute of Physics.