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ABSTRACT The light curves of radioactive transients, such as supernovae and kilonovae, are powered by the decay of radioisotopes, which release high-energy leptons through $$\beta ^+$$ and $$\beta ^-$$ decays. These leptons deposit energy into the expanding ejecta. As the ejecta density decreases during expansion, the plasma becomes collisionless, with particle motion governed by electromagnetic forces. In such environments, strong or turbulent magnetic fields are thought to confine particles, though the origin of these fields and the confinement mechanism have remained unclear. Using fully kinetic particle-in-cell (PIC) simulations, we demonstrate that plasma instabilities can naturally confine high-energy leptons. These leptons generate magnetic fields through plasma streaming instabilities, even in the absence of pre-existing fields. The self-generated magnetic fields slow lepton diffusion, enabling confinement, and transferring energy to thermal electrons and ions. Our results naturally explain the positron trapping inferred from late-time observations of thermonuclear and core-collapse supernovae. Furthermore, they suggest potential implications for electron dynamics in the ejecta of kilonovae. We also estimate synchrotron radio luminosities from positrons for Type Ia supernovae and find that such emission could only be detectable with next-generation radio observatories from a Galactic or local-group supernova in an environment without any circumstellar material.
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A particle-in-cell study of electrostatic potential well formation in an edge-confined non-neutral plasma
An edge-confined single-species plasma will relax to create a potential energy hill that climbs from the boundary. This hill represents a potential well for species of the opposite sign and can be a means to confine the second species. With this ultimate application in mind, we have studied the relation between the plasma temperature, the number of confined particles, and the electrostatic potential well that forms in a fully non-neutral plasma of electrons in a trapping volume with an artificially structured boundary (ASB). An ASB is a structure that produces periodic short-range static electric and magnetic fields for confining a plasma. To perform a detailed analysis on this topic, simulations using a particle-in-cell code have been performed. By varying the configurational elements of the ASB, such as the bias on the boundary electrodes and the internal radius of the structure, coupled with a course thermalization process and a prescribed threshold for particle leakage, potential well values were determined for a range of plasma temperatures and confinement conditions. Maximum well depths were observed below a threshold plasma temperature in each configuration. This study gives insight into the limitations of primary particle confinement with this type of structure and optimal conditions for the formation of a potential well that might be utilized to confine a second species.
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- Award ID(s):
- 1803047
- PAR ID:
- 10538202
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- AIP Advances
- Volume:
- 14
- Issue:
- 8
- ISSN:
- 2158-3226
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1063/5.0219656
