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Description
The intensity of the ion beam extracted from an electron cyclotron resonance ion source (ECRIS) depends on the production rate of ions and the efficiency of the ion beam formation and transport. The production of Ar$^{9+}$ ions in an ECRIS plasma and the beam formation of the resulting Ar$^{9+}$ ion beam have been studied with the JYFL $14~\mathrm{GHz}$ ECRIS by using optical emission spectroscopy and measuring the m/q analyzed beam current. The parametric dependence of the intensity of the $553.32650~\mathrm{nm}$ optical emission line resulting from a magnetic dipole transition between the metastable excited state $2\text{s}^22\text{p}^5~^2\text{P}^{\circ}_{1/2}$ and the ground state $2\text{s}^22\text{p}^5~^2\text{P}^{\circ}_{3/2}$ of Ar$^{9+}$ has been measured from a radial diagnostics port of the JYFL $14~\mathrm{GHz}$ ECRIS and compared to the intensity of extracted Ar$^{9+}$ ion beam current as a function of microwave power and neutral gas feed. The optical measurements have been done with high resolution ($31~\mathrm{pm}$ at FWHM) and high throughput Fastie-Ebert monochromator coupled with a photomultiplier tube detector with a phase-sensitive lock-in detection setup. The relative changes in both the optical emission and the beam have been compared and will be discussed. Microwave power dependency was confirmed with the transient measurements where the microwave power was adjusted rapidly. The results suggest that in case of Ar$^{9+}$ the production rate does not constrict the performance of the ECRIS at high microwave power but instead the beam formation could limit the extracted current.
