Diagnostics of the cesium amount in an RF negative ion source and the correlation with the extracted current density

The formation of negative ions in plasma sources by the surface process requires covering the extraction grid with a material of low work function. This can be achieved by cesium evaporation but for operational reasons the consumption of cesium should be minimised. In order to quantify the amount of cesium in the RF discharge optical emission spectroscopy is used as diagnostic tool. Suitable diagnostic lines and their analysis to obtain particle densities and particle fluxes are described. Influences of argon admixtures to hydrogen and deuterium discharges on cesium emission are shown. A correlation of the cesium emission with the extracted negative ion current density is discussed.