Experimental measurements of shifts and asymmetries of He II P_αand P_βspectral lines

Abstract

Red shifts and asymmetries of He II Pα 468.5682 nm and Pβ 320.3104 nm lines were measured in a pulsed plasma at an electron density measured by two-wavelength interferometry which ranges from 5.54 × 1022 m−3 to 7.48 × 1022 m−3 with uncertainty of 10%. Temperature ranges from 1.70 to 1.83 eV, and has been determined from intensities ratio of Pα and Pβ lines. Shifts for these lines were obtained using as reference lines Cd I 467.8149 nm and He I 318.7745 nm respectively. Measurements of asymmetries have been represented using reduced wavelength units. All results have been compared with previous experimental and theoretical data.

NeiiStark Width and Shift Regularities

“…The spectroscopic beam was limited by two diaphragms (D1, D2) 3 mm in diameter, and focused by a concave mirror ( M6) of 150 mm focal length onto the entrance slit (70 m width) of a Jobin-Yvon monochromator (1.5 m focal length, 2400 lines mm À1 holographic grating). The positions and diameters of diaphragms D1 and D2 ensure the observation of a homogeneous part of the plasma with variations in n e and T e less than 5% (Peláez et al 2005), due to the high cylindrical symmetry observed in the electron density and temperature spatial distributions .…”

“…All measurements were performed in second-order diffraction, with an exposure time of 5 s. In this configuration, the spectrometer has an inverse linear dispersion of 2.27 pm per channel at 295.0 nm and 1.8 pm per channel at 339.0 nm, with an uncertainty of about 0.6% (Peláez et al 2005).…”

Stark parameters of neutral helium 318.8 nm line

“…The algorithm used to obtain isolated profiles for these lines has been extensively explained in previous works (Rodríguez et al 2003;Peláez et al 2005). In our work, differences between experimental profiles and best fits are lower than 10%.…”

“…Therefore, these broadening mechanisms are shown to be negligible for this spectral line and these plasma conditions. To estimate shift, as in previous works (Peláez et al 2005), it was assumed that the centre of the line is the average of the middle points at heights between 25% and 75% of the maximum intensity. In order to obtain the relative shift, centres of He I 318.8 nm lines for different instants along the plasma life were fitted to a straight line, which takes null value when the electron density is zero.…”

“…Spectroscopic and interferometric end-on measurements were made on the lamp at two different plasma columns 3 mm in diameter and placed 2 mm off the lamp axis in the symmetrical positions relative to it. The validity of this method has already been proved (del Val et al 1998;Peláez et al 2005).…”