Submacropulse electron-beam dynamics correlated with higher-order modes in a Tesla-type cryomodule

TL;DR

This study investigates how higher-order electromagnetic modes in TESLA-type superconducting cavities influence electron-beam dynamics, revealing correlated submacropulse centroid shifts and oscillations, with implications for accelerator commissioning.

Contribution

It provides new experimental insights into the effects of long-range wakefields and HOMs on beam stability in cryomodules, aiding machine learning applications for accelerator optimization.

Findings

Observed submacropulse centroid slews of a few hundred microns.

Detected centroid oscillations at approximately 240 kHz.

Results will inform machine learning models for linac commissioning.

Abstract

Experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility to elucidate the effects of long-range wakefields (LRWs) in TESLA-type superconducting rf cavities. In particular, we investigated the higher-order modes (HOMs) generated in the eight cavities of a cryomodule (CM) due to off-axis steering with correctors located ~4 m upstream of the CM. We have observed correlated submacropulse centroid slews of a few-hundred microns and centroid oscillations at ~240 kHz in the rf BPM data after the CM. The entrance energy into the CM was 25 MeV, and the exit energy was 100 MeV with 125 pC/b and 400 pC/b in 50-bunch pulse trains. These experimental results were evaluated for machine learning training aspects which will be used to inform the commissioning plan for the Linac Coherent Light Source-II injector CM.