Direct large-area observation of subsurface plastic activity in conditioned copper electrodes
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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BibTeX
@misc{ashkenazy2026direct,
title = {{Direct large-area observation of subsurface plastic activity in conditioned copper electrodes}},
author = {Yinon Ashkenazy and Inna Popov and Victoria M. Bjelland and William L. Millar and Walter Wuensch},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.19192},
eprint = {2606.19192},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.19192},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Direct large-area observation of subsurface plastic activity in conditioned copper electrodes
AU - Yinon Ashkenazy
AU - Inna Popov
AU - Victoria M. Bjelland
AU - William L. Millar
AU - Walter Wuensch
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2606.19192
UR - https://arxiv.org/abs/2606.19192
AB - 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 E_S predicted by Monte Carlo simulations. These observations point to the evolving subsurface dislocation population as a candidate physical basis of conditioning.
ER -