Effect of collisional quenching on the measurement of ion species mix in neutral beam injectors

Abstract

A corona model is used in analyzing the Doppler shifted spectroscopy (DSS) data for estimating the ion species mix and beam species fractions in positive ion based neutral beam injectors. In this model the excited neutral atom is assumed to decay solely by a spontaneous radiative process. However, at the beam energies of 20–60 keV/amu, collisional quenching of the excited neutrals affects these estimations when background pressure exceeds 1 mTorr. We present here a modified corona model that takes into account the effects of collisional quenching. We also describe the results of application of the present model to a typical DSS data obtained in the first phase of operation of the SST-1 neutral beam injector.

Spectroscopic determination of the composition of a 50 kV hydrogen diagnostic neutral beam

“…We determined the dependence of the ion source electron density under various conditions by measuring the Stark broadening of the H β line 4 and the ions species fractions via the Doppler shifted H α line. [5][6][7][8][9][10] Figure 1 shows the experimental setup for the ion source electron density and beam components measurement. The axial view is used to measure the ion source density and the view through a side port is used to measure the Dopplershift spectrum.…”

Effect of sublevel population mixing on the interpretation of doppler-shift spectroscopy measurements of neutral beam content

“…This value sufficiently exceed estimated cross-section of l-mixing in collisions with molecular hydrogen ( [13,14]). Based on this relation, Bharathi and Prahlad [15] argued that effect of collisional l-mixing can be neglected. At the same time apart from collisions with hydrogen molecules there are several another processes that cause l-mixing and satisfy mentioned conditions.…”

Study on production and extraction of negative impurity ions in a caesiated negative ion source

“…Since the inception of neutral beam injectors, spectroscopy-based diagnostics, often referred as Doppler shift spectr oscopy diagnostics (DSS), has proved to be an indispensable tool for characterizing energetic neutral beams. Estimation of many important beam parameters is routinely carried out using this diagnostics [7][8][9]. In this technique, the emissions from excited fast neutral atoms (produced via the neutralization of charged particles and the impact excitations of neutrals) are observed at an angle to the axis of the beam.…”

“…Additionally, if there are extracted molecular ions then they dissociate during the neutralization process and produce fast atoms corresponding to their equally partitioned kinetic energies. However, the emissions from these atoms are now Doppler shifted by different magnitude and the resultant spectra show a series of resolved peaks [8,9]. In ROBIN, Doppler shift spectroscopy diagnostics is performed in the drift region, to measure the beam divergence, beam inhomogeneity and stripping losses.…”

“…In these studies, it was found that the magnitude of the Doppler shift showed a value corresponding to ~E/18. For an energy of ~E/18 to be observed, an impurity ion with a mass of 18 amu is required [9][10][11][12]. This peak is attributed to the photons emitted by fast neutrals which are produced from the dissociation of hydrogen-bearing impurity ions such as H 2 O + /H 3 O + /OH + , extracted with an energy E. However, it is important to note that in experiments based on negative ion sources, no specific study on this peak is reported in the literature.…”