Experimental and theoretical evaluation of the HeII6560.1 Å line contribution to the deuterium Dα spectral line shape in Tore Supra Ergodic Divertor plasmas

Abstract

The spectral profile of the deuterium Dα line (a common diagnostic of recycling particles in present tokamaks), emitted in front of an equatorial neutralizer plate in Ergodic Divertor Tore Supra plasmas, shows, in the presence of large helium contents, some features which have been interpreted as the contribution of the near-by hydrogen-like helium Brβ line intensity. In order to validate this interpretation, the intensities of several other He II lines have been measured, and their ratios compared to theoretical values calculated from a collisionalradiative model. These data have been used to estimate the brightness of the He II Brβ line. Although the effect of the He II Brβ line intensity on the Dα line profile shape is evaluated (and measured) to be non-negligible in these ad hoc plasmas (having a large helium content), it is concluded that it should be of no influence in usual fusion plasmas.

Analysis of asymmetric Dα spectra emitted in front of a neutralizer plate of the Tore-Supra ergodic divertor

“…It should be noted that in Tore-Supra, even in pure deuterium discharges, helium is present because of wall conditioning with helium glow discharges. In recent papers [10,18], we have shown, using a collisional-radiative model and measured intensities of hydrogen-like helium lines from the Brackett series, that the He + Brβ line does not affect the Dα line in usual discharges such as those considered in this paper. The second step is to identify all the mechanisms and effects contributing to the splitting and the broadening of the line.…”

“…Moreover, neutrals created with E 0 = 0.3 eV are released in the excited state n = 3 or in the ground state n = 1, whereas those created with E 0 = 1.5 eV are in state n = 3 [1]. For the time of flights obtained from equation (18), only one excitation in state n = 3 is expected. The collisionality parameter (νt) for cold neutrals is obtained from equation (5), in which we thus use p = 1 for atoms created in their ground state and p = 2 for those released in n = 3.…”

Atomic and molecular deuterium edge density evaluation from spectral analysis of the Dα line shape

“…Since wall conditioning of the Tore Supra tokamak is routinely performed with helium glow discharges, varying amounts of helium are often present in the plasma. However, a detailed study, based on a CR model and experimental measurements, has shown that the He II 6560 Å line brightness is negligible compared to Dα in normal deuterium plasmas (Guirlet et al 2001).…”

“…(x)n e (x) dx R 1 (x s )n e (x s )L χ (x) + R 2 (x)/r D (x)]n e (x) dx [R 1 (x s ) + R 2 (x s )/r D (x s )]n e (x s )L(14) …”

Neutral helium line emission for edge plasma conditions

“…Recombination processes are responsible for the plasma detachment and the spectroscopic investigation of the corresponding radiation emission is therefore of great interest [e.g., [1][2][3]]. However, molecular recombination processes involved are very complex (e.g., vibrationally excited hydrogen molecules) and it is desirable to avoid them as they are difficult to model.…”