Using the Radiation of Hydrogen Atoms and Molecules to Determine Electron Density and Temperature in the Linear Plasma Device PSI-2

In this work we investigate the applicability of several optical emission spectroscopy methods to measure the electron density and temperature in deuterium plasma in the linear plasma generator PSI-2. The spectroscopy measurements are realized by an imaging spectrometer which delivers radial profiles of the emission lines. With the application of an inverse Abel transformation, spatially resolved measurements are obtained.

The spectroscopy methods divide into two groups: The measurement of n_e by Balmer line ratios and by the rotational temperature of molecules is only suitable for ionizing plasmas; the measurement of n_e by the Stark broadening of Paschen lines and of T_e by Paschen line ratios is only applicable for recombining plasmas.

For the evaluation of these methods, different plasma conditions are produced in PSI-2. The plasma generator is capable of producing deuterium plasmas with electron densities of up to 10¹³ cm^-3 and electron temperatures of up to 20 eV. Additional measurements with a Langmuir double probe are conducted for comparison with the spectroscopy measurements.

A collisional-radiative model in the Yacora code is used to compare measured Balmer line emissions with the calculation and to investigate which reaction channels influence the recombination in PSI-2.