The anomalous currents in the front foils of the JET lost alpha diagnostic KA-2

F.E. Cecil, V. Kiptily, Antti Salmi, JET EFDA Contributors

    Research output: Contribution to journalArticleScientificpeer-review

    5 Citations (Scopus)

    Abstract

    We have examined the observed currents in the front foils of the JET Faraday cup lost alpha particle diagnostic KA-2. In particular, we have sought to understand the currents during Ohmic plasmas for which the ion flux at the detectors was initially assumed to be negligible. We have considered two sources of this current: plasma ions (both deuterium and impurity) in the vicinity of the detector (including charge exchange neutrals) and photoemission from scattered UV radiation. Based upon modeling and empirical observation, the latter source appears most likely and, moreover, seems to be applicable to the currents in the front foil during ELMy H-mode plasmas. A very thin gold or nickel foil attached to the present detector aperture is proposed as a solution to this problem, and realistic calculations of expected fluxes of lost energetic neutral beam ions during TF ripple experiments are presented as justification of this proposed solution.
    Original languageEnglish
    Article number10D326
    JournalReview of Scientific Instruments
    Volume81
    Issue number10
    DOIs
    Publication statusPublished - 2010
    MoE publication typeA1 Journal article-refereed

    Keywords

    • deuterium
    • gold
    • nickel
    • plasma diagnostics
    • plasma impurities
    • plasma toroidal confinement
    • plasma transport processes
    • Tokamak devices

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