Resumen de Optimization of remote inductively coupled plasma for the cleaning of different optical surfaces
The main goal of this research project was to further develop an in-situ plasma process – inductively coupled plasma (ICP) – in order to clean a variety of different optical coatings and components subject to carbon contaminations. These optics are typically used in accelerator-based light sources, therefore specific plasma requirements need to be fulfilled in order to preserve the performance and the quality of the optical coatings as well as their ultra-high vacuum (UHV) environment.
The reason for choosing the inductively coupled plasma (ICP) was to explore a new technique based on an already known concept.
Thus, the first three chapters of this thesis give an introduction to the plasma fundamentals focused on ICP as used in cleaning applications. Also, a brief introduction on the basis of accelerator-based light sources facilities is given, showing the different types of optical components and optical coatings typically used in these facilities. This first part of the thesis is concluded with a detailed description of the experimental setup and the different techniques used to characterize the optical components before and after the plasma treatments Chapter four presents a study regarding the low-pressure RF plasma cleaning of carbon contaminated B4C test samples via inductively coupled O2/Ar, H2/Ar, and pure O2 RF plasma. In addition, chapter five shows the results from cleaning processes performed on three different materials such as Ni, Rh, and Al by using two different gas mixtures N2/O2/H2 and N2/H2 plus a subsequent cleaning of Al EUV filters previously used at the FERMI FEL by using an N2/H2 plasma.
In chapter six entitled "Plasma Diagnostics", a further experimental part is presented, which focuses on a series of measurements on different plasma feedstock gas configurations by means of Langmuir Probe (LP) and Mass Spectrometry (MS). At the end of this chapter a series of conclusions, concerning the analysis and the results obtained are drawn, which lay the foundation for a better understanding of the carbon cleaning process.
Finally, the Ph.D. thesis ends with chapter seven, in which information from the cleaning process performed on an Au test mirror with identical characteristics than the M1 front mirror at the CIRCE beamline is given and further plasma chemistry aspects are developed.
