This slow-motion simulation animation shows electromagnetic wakefields an electron “bunch” generates as it travels through a cryomodule of the planned International Linear Collider. Yellow and red indicate a strong wakefield; green and blue indicate weaker fields. Top: The full cryomodule. Middle: Expanded views of the power couplers and higher-order mode (HOM) couplers at the cavity ends. Bottom: Cryomodule closeup.