Absolute ion density measurement (MAID) by evaluating ion acoustic waves in the plasma accompanied by modeling for ion identification

• Applicant: Dr. Torsten Gerling
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 466331904

Despite atmospheric pressure plasma discharges being investigated intensively since over a decade, the determination of absolute ion densities still proves a challenging topic in plasma diagnostics. The common approach with commercial mass spectrometers deliver relative values and actinometry as well as modelling deliver absolute ion densities while requiring specific boundary conditions.By evaluating self-excited ion acoustic waves (IAW) in the plasma, the proposed project addresses the determination of absolute ion densities by current signal measurement. Previous results and calculations show the existence of oscillations on the current signal once the ion densities cross a lower threshold. The evaluation of the oscillation frequency equal to the plasma ion frequency revealed the absolute ion density with a high time resolution within nanoseconds.The presented project addresses the following scientific questions:• Is there a correlation between occurrence of IAW and the ion polarity or gas composition; is it possible to observe IAW generated by negative ions• Is the nature of IAW excitation based on self excitation or an external excitation purely due to the fast rising current pulse of the transient spark• Is it possible to observe an IAW within a single filament of the DBD and which parameters can be determined• Is it possible to observe IAW within modeling results• Is an external excitation of IAW possible and could this allow a tuning of the detection limitAside from the application of the proposed diagnostic on the already successful transient spark discharge, the investigation of a dielectric barrier discharge (DBD) with a broader scientific database is targeted. The DBD allows the operation at different gases including admixtures. By accompanying modelling the expected ion densities and dominant ions will be calculated to support ion identification. At the end of the project the until now passive diagnostic shall be converted into an active diagnostic by coupling a high frequency excitation into the electrical system. An active diagnostic might allow the ion density measurement at any desired plasma setup.

• DFG Programme: Research Grants
• Co-Investigator: Privatdozent Dr. Detlef Loffhagen