京都大学 / 新制・課程博士 / 博士(理学) / 甲第23457号 / 理博第4751号 / 新制||理||1681(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 前里 光彦, 教授 北川 宏, 教授 竹腰 清乃理 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

A Penning-type surface-plasma negative hydrogen (H^-) ion source has been delivering beam at the ISIS pulsed spallation neutron and muon facility for over thirty years. It is one of the most powerful and well-renowned H^- sources in the world. Although long-term experience has allowed the source to be operated reliably and set up in a repeatable way, it is treated as something of a 'black box': the detailed plasma physics of why it works has always been unclear. A vacuum Vessel for Extraction and Source Plasma Analyses (VESPA) has been developed to understand the ISIS ion source plasma and improve the beam extracted from it. The VESPA ion source is operated in a completely new regime whereby the analysing sector dipole magnet housed inside a refrigerated 'cold box', presently used on ISIS, is replaced by an on-axis extraction system. The new extraction system incorporates a novel einzel lens with an elliptical aperture. This is the first demonstration of an elliptical einzel being used to focus an asymmetric H^- ion beam. With the dipole magnet removed, the ion source has been shown to produce 85 mA of H^- beam current at normal settings; of which 80 mA is transported through the new einzel lens system, with a normalised RMS emittance of 0.2 π mm mrad. Optical emission spectroscopy measurements have shown a plasma density of 10¹⁹ m^–3, an H₂ dissociation rate of 70%, an almost constant electron temperature of 3.5 eV and an atomic temperature which linearly increases above the electron temperature. In support of these principal measurements, rigorous particle tracking, electrostatic and thermal simulations were performed. In addition, a suite of new equipment was manufactured by the author. This includes a fast pressure gauge, a temperature controller, a high voltage einzel lens circuit, a fast beam chopper and a caesium detection system.