Abstract
The target parameters of negative ion sources regarding the current of extracted negative ions, the current of co-extracted electrons, the pulse duration, the duty cycle, and the availability of the system can be rather strict. Knowledge of plasma parameters such as the electron temperature and the electron density and also properties of molecules or photon fluxes can provide essential insights into the ion source physics needed for reaching the target parameters. Emission spectroscopy is a non-invasive tool enabling access to line-of-sight averaged values of plasma parameters. This paper gives an overview of the application of emission spectroscopy in the visible range, extended for long wavelengths to the near-IR and for short wavelengths to the vacuum ultraviolet (VUV)/UV range. The amount of information to be gained from measured emission spectra is directly correlated with the effort invested for calibrating the system. Examples are given, ranging from simple monitoring to the complex evaluation of molecular spectra and the determination of highly energetic photon fluxes in the VUV/UV range. Additional emphasis is laid on the population models needed for the interpretation of measured spectra.
Highlights
Ion sources for negative hydrogen ions (H− and D−) are commonly used for different applications, most prominent being the source for producing brilliant proton beams in accelerator facilities or the source for producing energetic neutral particles for neutral beam injection systems of fusion devices
One of the most prominent and easy-to-use diagnostics being non-invasive is emission spectroscopy, covering the wavelength range from the vacuum ultraviolet range (VUV) range to the infrared range
Optical emission spectroscopy is a versatile diagnostic tool routinely applied in negative hydrogen ion sources
Summary
Ion sources for negative hydrogen ions (H− and D−) are commonly used for different applications, most prominent being the source for producing brilliant proton beams in accelerator facilities or the source for producing energetic neutral particles for neutral beam injection systems of fusion devices (for an overview, see, for example, Ref. 1). In plasmas for negative hydrogen ion sources, this effect can be relevant only for resonant atomic emission lines.
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