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Space-Charge Effects in the Field-Assisted Thermionic Emission from Nonuniform Cathodes

Anna Sitek, Kristinn Torfason, Andrei Manolescu, and Ágúst Valfells
Phys. Rev. Applied 15, 014040 – Published 21 January 2021

Abstract

We use computational simulations to study the electron emission and propagation in planar vacuum diodes. We show how space charge affects thermionic emission from cathodes with two different values of work function that form a checkerboard pattern of finite extent on the cathode surface. We confirm that, for intermediate cathode temperature, the local current density from low work function regions can exceed the space-charge limit for the entire cathode. As the cathode temperature rises, space-charge effects lead to homogeneous current density from the interior of the emitting area and a higher current density from its periphery. We show how beam emittance and brightness are affected, and show that the operating temperature for optimal brightness is such that it corresponds to the transition region between source-limited and space-charge-limited emissions. Finally, we show how beam current and beam quality depend on how fine grained the structure of the cathode is.

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  • Received 29 September 2020
  • Accepted 14 December 2020

DOI:https://doi.org/10.1103/PhysRevApplied.15.014040

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Nonlinear DynamicsAccelerators & Beams

Authors & Affiliations

Anna Sitek1,2,*, Kristinn Torfason1, Andrei Manolescu1, and Ágúst Valfells1

  • 1Department of Engineering, Reykjavik University, Menntavegur 1, IS-102 Reykjavik, Iceland
  • 2Department of Theoretical Physics, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland

  • *anna.sitek@pwr.edu.pl

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Vol. 15, Iss. 1 — January 2021

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