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Evaluation of Hydrogen Radical Production Using the Hydrogen Balmer-α Absorption Spectrum

Yuya INOKUCHI¹⁾, Kazutaka MITSUI²⁾, Toshiro KASUYA¹⁾, Hidenori TAKAHASHI²⁾, Yoshihiro YAMADA²⁾, Takahiro KENMOTSU¹⁾, Shinichi IWAMOTO²⁾, Koichi TANAKA²⁾, Motoi WADA¹⁾

1)

Doshisha University, Kyotanabe, Kyoto 610-0321, Japan

2)

Shimadzu Corporation, Nakagyoku, Kyoto 604-8442, Japan

(Received 13 May 2025 / Accepted 17 September 2025 / Published 5 December 2025)

Abstract

An ECR (Electron Cyclotron Resonance) discharge can serve as an efficient atomic hydrogen beam source for a bio-molecule mass analysis system through detecting fragment ions produced from the HAD (Hydrogen Attachment/Abstraction Dissociation) process. A simple diagnostics system that measures the absorption of photons from a light emitting diode located at the opposite side of the ECR plasma is coupled to a 4 mm inner diameter glass tube discharge source driven by a 2.45 GHz microwave. The obtained result for a fixed microwave input power shows a simple linear correlation between the duty cycle and the absorption indicating the production rate of atomic hydrogen is constant over the discharge duration. The dependence of absorption rate upon the discharge power and that upon pressure indicated that the efficiency of the atomic hydrogen production rate tend to saturate at higher power and higher pressure. The wavelength spectrum of Balmer-α light emission showed a possibility that high-speed atomic hydrogen may exist in an intense ECR discharge.

Copyright (c) 2025 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

optical emission spectroscopy, ECR plasma, atomic source, absorption spectroscopy

DOI: 10.1585/pfr.20.1406051

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