Study of Possibility of Quantification of the Cesium Deposition on the Plasma Grid Plate by Image Processing Techniques

Abstract

ROBIN is an inductively coupled Radio Frequency (100kW, 1MHz) based negative hydrogen ion source experiment facility at Institute for Plasma Research. Plasma production and experiments for extraction of negative ion beams are carried out in ROBIN. The facility incorporates cesium oven, grid and source component heating, cesium diagnostic system, inert gas-based source venting and Doppler shift spectroscopy diagnostic system. In surface mode of operation, Cesium (Cs) vapor is injected in the source to lower work-function of the grid surface and to enhance the negative ion production by surface process. Due to low melting point (near room temperature), cesium vapor gets condensed on unheated surfaces and makes cold spots either in the oven location or in the Cs vapor delivery tube or even inside the source chamber. After many iterations some Cs is deposited on the surface of plasma grid plate. Electron generation can be disrupted due to excessive amount of Cs on the surface. It is necessary to clean Cs deposit from time to time. The work was carried out to develop image processing techniques for the quan- tification of Cs deposition on surface of plasma extraction grid plate. It was found out that quantification of cesium layer, which is usually thick by few nanometers to few micrometers only, cannot be done using image processing techniques due to extremely thin layer. Three other possible techniques for quantification of the Cs layer: thermal Imaging, X-Ray difraction and LASER based measurement tech- nique were also explored. Image processing techniques based on texture analysis were studied and implemented to find the locations of cesium deposits. It was concluded that, such a thin layer cannot be quantified using image processing techniques due to layer being thick by few micrometers to few nanometers only. Image segmentation and texture analysis methods were used to identify the locations of cesium deposits.