Abstract
Experiment showing a strong reduction of undulator emission for a `quiet' beam which represents the first demonstration of Dicke's subradiance of dipole radiation in the context of free electrons.
Highlights
Dicke’s seminal work on superradiance [1] describes the process of controlling radiation through a system’s collective properties; in Dicke’s superradiance the cooperative emission of e.g., dipoles radiating in phase increases the total radiation, while in subradiance, antiphasing of the dipoles leads to cancellation between the radiation fields and reduced radiation
In this paper we present experimental observation of a strong reduction in undulator radiation, demonstrating the feasibility of noise suppression as a practical tool in accelerator physics
Dicke’s results have received most attention from the field of atomic physics [3,4,5], but subradiance is directly applicable to relativistic free electrons; e.g., a microbunched electron beam emits superradiantly when oscillating transversely in a magnetic undulator, with the intensity enhanced relative to spontaneous radiation by the number of coherent electrons [6,7]
Summary
Dicke’s seminal work on superradiance [1] describes the process of controlling radiation through a system’s collective properties; in Dicke’s superradiance the cooperative emission of e.g., dipoles radiating in phase increases the total radiation, while in subradiance, antiphasing of the dipoles leads to cancellation between the radiation fields and reduced radiation. The experimental scheme follows the dispersive method of [10]: space charge (Coulomb) interaction occurs in a region of length La, creating an energy modulation, and a subsequent magnetic chicane of dispersive strength R56 generates a corresponding density modulation. Note that this model is identical to that of MBI (see e.g., [29] for an overview). R56, to the interaction strength, n0A, produces Υ 1⁄4 1 and sends the noise factor FðkÞ → 0, generating a “quiet” beam When this quiet beam passes through an undulator, we expect a corresponding decrease in undulator radiation, i.e., subradiance
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