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arXiv · 1807.04332

Submacropulse Electron-Beam Dynamics Correlated With Higher-Order Modes In Tesla-Type Superconducting RF Cavities

A. H. Lumpkin·R. Thurman-Keup·D. Edstrom·J. Ruan·N. Eddy·P. Prieto·O. Napoly·B. E. Carlsten·K. Bishofberger
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Abstract

We report the direct observations of sub-macropulse beam centroid oscillations correlated with higher order modes (HOMs) which were generated by off-axis electron beam steering in TESLA-type superconducting RF cavities. The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility using its unique configuration of a photocathode rf gun injecting beam into two separated 9-cell cavities in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. Oscillations of ~100 kHz in the vertical plane and ~380 kHz in the horizontal plane with up to 600-μm amplitudes were observed in a 3-MHz micropulse repetition rate beam with charges of 100, 300, 500, and 1000 pC/b. However, the effects were much reduced at 100 pC/b. The measurements were based on HOM detector circuitry targeting the first and second dipole passbands, rf BPM bunch-by-bunch array data, imaging cameras, and a framing camera. Calculations reproduced the oscillation frequencies of the phenomena in the vertical case. In principle, these fundamental results may be scaled to cryomodule configurations of major accelerator facilities.

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A. H. Lumpkin, R. Thurman-Keup, D. Edstrom, J. Ruan, N. Eddy, P. Prieto, O. Napoly, B. E. Carlsten, K. Bishofberger. 2018-07-11. Submacropulse Electron-Beam Dynamics Correlated With Higher-Order Modes In Tesla-Type Superconducting RF Cavities. https://doi.org/10.1103/physrevaccelbeams.21.064401

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