Upgraded millimeter-wave interferometer for measuring the electron density during the beam extraction in the negative ion source

T Tokuzawa; M Kisaki; K Nagaoka; K Tsumori; Y Ito; K Ikeda; H Nakano; M Osakabe; Y Takeiri; O Kaneko

doi:10.1063/1.4959841

Upgraded millimeter-wave interferometer for measuring the electron density during the beam extraction in the negative ion source

Rev Sci Instrum. 2016 Nov;87(11):11E105. doi: 10.1063/1.4959841.

Authors

T Tokuzawa¹, M Kisaki¹, K Nagaoka¹, K Tsumori¹, Y Ito¹, K Ikeda¹, H Nakano¹, M Osakabe¹, Y Takeiri¹, O Kaneko²

Affiliations

¹ National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan.
² National Institutes of Natural Sciences, 4-3-13 Toranomon, Minato-ku, Tokyo 105-0001, Japan.

PMID: 27910614
DOI: 10.1063/1.4959841

Abstract

The upgraded millimeter-wave interferometer with the frequency of 70 GHz is installed on a large-scaled negative ion source. Measurable line-averaged electron density is from 2 × 10¹⁵ to 3 × 10¹⁸ m^-3 in front of the plasma grid. Several improvements such as the change to shorter wavelength probing with low noise, the installation of special ordered horn antenna, the signal modulation for a high accuracy digital phase detection, the insertion of insulator, and so on, are carried out for the measurement during the beam extraction by applying high voltage. The line-averaged electron density is successfully measured and it is found that it increases linearly with the arc power and drops suddenly at the beam extraction.