Volumetric Recombination in the Linear ECR Plasma Device NUMBER

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A plasma recombination experiment was carried out using the linear electron cyclotron resonance (ECR) plasma device NUMBER as a preliminary step for forming a detached plasma. The electron density measured by an electrostatic probe in a divertor-simulated region was successfully increased up to approximately 6×10¹⁷ m⁻³. This increase was realized by installing an additional gas feed system to the region and using a circular polarizer to control the microwave polarization. Passive spectroscopic measurements performed on the high-density plasma yielded line spectra of He I 2³P−n³D for the principal quantum number n ≤13, which are characterstic of helium recombining plasma. The line spectra were used to calculate an electron temperature of approximately 0.055 eV and an electron density of approximately 1.33 × 10¹⁸ m⁻³ by the Boltzmann plot method and Saha–Boltzmann equation, respectively.