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Direct large-area observation of subsurface plastic activity in conditioned copper electrodes

Y. Ashkenazy1,2,*, I. Popov2, V. M. Bjelland3,4, W. L. Millar3, and W. Wuensch3

  • *Contact author: yinon.ash@mail.huji.ac.il
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Phys. Rev. Accel. Beams 29, 103503 – Published 28 October, 2026

DOI: https://doi.org/10.1103/stzb-pjd8

Abstract

High-field conditioning is the process by which radio-frequency structures in particle accelerators and other high-gradient devices reach their operating fields, yet the underlying physical mechanism remains an open question. Models and indirect measurements point to subsurface dislocation dynamics, but large-area structural measurements have been missing. We present electron backscatter diffraction measurements spanning millimeter-scale regions on a copper cathode conditioned at pulsed direct-current fields up to ∼80  MV/m in a sloped-anode geometry, which imposes a known gradient of field exposure across a single electrode. Across nine regions of interest spanning this exposure range, the mean intragrain misorientation of field-exposed regions exceeds that of unexposed references by ∼75%; the difference is reproduced by three independent misorientation metrics and confirmed by Kolmogorov-Smirnov tests. To our knowledge, this is the first large-area observation of structural differences between conditioned and unconditioned regions of a high-field electrode. The misorientation separates into three tiers (high-field center and edge, low-field periphery, and unexposed reference) that match the spatial profile of the conditioning-state variable ES predicted by Monte Carlo simulations. These observations point to the evolving subsurface dislocation population as a candidate physical basis of conditioning.

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Phys. Rev. Accel. Beams 29, 103503– Published 28 October, 2026
  • Received 23 June 2026
  • Accepted 16 October 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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