DOI: 10.5281/zenodo.4383404
title: Signature of gas mixing and isotope anomaly in neon ECR plasma

description: Figure 1: The schematic view of the experimental set up (A subsection of the LEIBF). Figure 2: A typical beam profile; the beam before analysis (left), <sup>20</sup>Ne<sup>+4</sup> after analysis (right). The peak height and peak width govern the beam intensity and beam size, respectively. The analyzed beam spot was ~ 3 mm in the diameter Figure 3: At E/q = 100, 200 and 300 kV; the charge state distribution of <sup>20</sup>Ne (top), the charge state distribution of <sup>22</sup>Ne (middle) and the intensity ratio of <sup>22</sup>Ne to<sup>20</sup>Ne for various charge states (bottom). Figure 4: At E/q = 200 kV, the intensity ratio of <sup>22</sup>Ne to <sup>20</sup>Ne as a function of charge states for pure natural and oxygen mixed (at 25, 50 and 75 %) ECR plasma Figure 5: At E/q = 200 kV, the intensity ratio of <sup>22</sup>Ne to <sup>20</sup>Ne as a function of charge states for pure natural and helium mixed (at 25, 50 and 75 %) ECR plasma Figure 6: At E/q = 200 kV, the charge state distribution of pure <sup>20</sup>Ne plasma and its comparison with that of mixed with O<sub>2</sub> and He; with 25 % mixing (top), with 50 % mixing (middle) and with 75 % mixing (bottom) Figure 7: At E/q = 200 kV, the charge state distribution of pure <sup>22</sup>Ne plasma and its comparison with that of mixed with O<sub>2</sub> and He; with 25 % mixing (top), with 50 % mixing (middle) and with 75 % mixing (bottom) Figure 8: The dependence of neon isotope anomaly as a function of the charge state. A polynomial of degree 2 fits the experimental data well. We have reported the isotope anomaly and the gas mixing (He & O<sub>2</sub>) effects in Ne ECR plasma populated with maximum charge state of +7 using a 10 GHz all-permanent-magnet NANOGAN ECR ion source. The ion intensity ratio of <sup>22</sup>Ne to <sup>20</sup>Ne in pure plasma condition showed clear signature of the anomalous effect, which starts quenching with increasing the fraction of mixing gases. The charge state dependence of the isotope anomaly follows a polynomial of degree 2. Compared to O<sub>2</sub>, the insertion of helium gas in the neon plasma has strong impact on deterioration of the isotope anomaly. The measured beam intensities of different charge states of both highly abundant neon isotopes (<sup>22</sup>Ne & <sup>20</sup>Ne) were high at high E/q (300 kV). However, the anomalous effect was prominent at E/q = 200 kV owing to mass dependent focusing properties of the ion optical lenses. In comparison to helium, O<sub>2</sub> gas mixing was noticed to be more effective for neon plasma. The mixing effect increases with increases fraction of O<sub>2</sub> in the plasma. Further, <sup>20</sup>Ne showed mixing effect at charge state lower than that of <sup>22</sup>Ne. Contrary to previous study on Kr plasma which could only be explained considering nonlinear effects, the observed trends in the isotope anomaly of Ne plasma are in good agreement with the prediction of linear Landau damping theory. The previous studies with Xe and Kr plasma and present results further confirm the strong influence of the relative mass difference on the isotope anomaly. The establishment of generalized selective ion heating mechanism in the plasma still requires enough experimental results on several isotopes with different mixture ratio.