2019/12/10 by I. V. Izotov, O. Tarvainen, Izotov, Ivan +13
Engineering · Physics and Astronomy · #FOS: Physical sciences #Magnetic confinement fusion research #Particle accelerators and beam dynamics #Plasma Diagnostics and Applications #Plasma Physics (physics.plasm-ph)
paper · pdf · doi:10.48550/arxiv.1912.04562
openalex publication_date 2019/12/10 · openalex created_date 2022/07/26 · openalex updated_date 2026/07/28
Further progress in the development of ECR ion sources (ECRIS) requires\ndeeper understanding of the underlying physics. One of the topics that remains\nobscure, though being crucial for the performance of the ECRIS, is the electron\nenergy distribution (EED). A well-developed technique of measuring the EED of\nelectrons escaping axially from the magnetically confined plasma of an ECRIS\nwas used for the study of EED in unstable mode of plasma confinement, i.e. in\nthe presence of kinetic instabilities. The experimental data were recorded for\npulsed and CW discharges with a room-temperature 14 GHz ECRIS at the JYFL\naccelerator laboratory. The measurements were focused on observing differences\nbetween the EED escaping from a stable and unstable plasmas. It was found that\nnonlinear phenomena alter the EED noticeably. The electron losses are enhanced\nin both unstable regime and with two-frequency heating suppressing the\ninstabilities. It has been shown earlier that two-frequency heating boosts the\nECRIS performance presumably owing to the suppression of instabilities. We\nreport the observed changes in EED introduced by the secondary frequency in\ndifferent regimes, including an off-resonance condition where the secondary\nfrequency is lower than the minimum frequency satisfying the resonance\ncondition for cold electrons at the magnetic field minimum. Finally, we suggest\nan experimental method of qualitative evaluation of the energy distribution of\nelectrons confined in the magnetic trap using a method of measuring energy\ndistribution of lost electrons during the plasma decay in pulsed operation of\nthe ion source.\n