Gamma diagnostics for the APEX collaboration
POSTER
Abstract
Annihilation gamma rays will be a primary means of diagnosing the low-temperature, e+e- pair plasmas that the APEX collaboration is working toward creating and studying -- both in a compact levitated dipole trap (APEX-LD) and in an optimized stellarator (EPOS). Even when positrons are below plasma densities (i.e., they have no collective interactions among themselves), they represent a sensitive probe for particle dynamics & transport -- whether in vacuum magnetic fields or through interactions with electrons, ions, or neutrals. An array of BGO detectors has been assembled and commissioned. A subset of the array was used to study the injection, confinement (including toroidal dynamics – due to spatial and velocity spreads), and loss mechanisms of positron bunches in a supported dipole trap (based on a permanent magnet). Measurements with the full array have been benchmarked with radioactive sources. Modeling of full-orbit e+ trajectory simulations and gamma ray scattering yields very good agreement with the experiments.
*The APEX Collaboration gratefully acknowledges support from the Helmholtz Association; the Federal Ministry of Research, Technology and Space (BMFTR); the Deutsche Forschungsgemeinschaft (DFG); the Alexander von Humboldt Foundation; the UC San Diego Foundation; the Deutscher Akademischer Austauschdienst (DAAD) RISE program; the United States Department of Energy; the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme; the Japan Society for the Promotion of Science (JSPS); and the National Institute for Fusion Science (NIFS).
Presenters
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Stefan Nissl
- Max Planck Institute for Plasma Physics