Volumetric Recombination in the Linear ECR Plasma Device NUMBER

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.