Studies of pure and nitrogen gas mixed xenon ECR plasma: Signature of abundance dependent unusual trends in isotope anomaly

We report the effect of N-2 gas-mixing in the xenon electron cyclotron resonance (ECR) plasma, and abundance-dependent novel, exciting and unusual trends of the isotope anomaly. The xenon plasma was produced using a 10 GHz all-permanent-magnet NANOGAN ECR ion source, and the charge state distributions of naturally abundant six stable xenon isotopes with and without N-2 gas-mixing (at 25%, 50%, and 75%) were recorded. The intensity ratio of the heavier to lighter isotope, where the heavier isotope is less abundant, showed a clear signature of the isotope anomaly as explained by the linear Landau wave damping theory. Contrary to the theoretical prediction that the isotope anomaly should vanish with a relatively large fraction of the heavier isotope in mixed plasmas, the trends of intensity ratios observed in such cases are very unusual and have almost the mirror-symmetrical shapes of those trends recorded with less abundant heavier isotope. Further, the effect of relative mass difference on the isotope anomaly was also evidenced. The N-2 gas-mixing of the xenon plasma at 25% and 50% shifted the entire charge state distribution toward the higher intensity side owing to the supply of additional electrons that caused high ionization efficiency. However, a prominent gas-mixing effect was observed at 75% of N-2 mixing in the xenon plasma beyond the +7 charge state. The abundance-dependent unusual trends in isotope anomaly have been explained by considering different ionic temperatures, ion heating by the wave damping, and Coulomb scattering in the core of the plasma.

Automated summary

In this study, we investigated the effect of N-2 gas-mixing on xenon electron cyclotron resonance (ECR) plasma and discovered novel and unusual trends in the isotope anomaly. By recording the charge state distributions of six stable xenon isotopes with and without N-2 gas-mixing, we found clear signatures of the isotope anomaly. Contrary to theoretical predictions, the unusual trends in intensity ratios observed in mixed plasmas with a large fraction of the heavier isotope support the presence of the isotope anomaly.