Generation of High-Power, Reversed-Cherenkov Wakefield Radiation in a Metamaterial Structure

Abstract

We present the first demonstration of high-power, reversed Cherenkov wakefield radiation by electron bunches passing through a metamaterial structure. The structure supports a fundamental TM-like mode with a negative group velocity leading to reversed Cherenkov radiation, which was clearly verified in the experiments. Single 45 nC electron bunches of 65 MeV traversing the structure generated up to 25 MW in 2 ns pulses at 11.4 GHz, in excellent agreement with theory. Two bunches of 85 nC with appropriate temporal spacing generated up to 80 MW by coherent wakefield superposition, the highest RF power that metamaterial structures ever experienced without damage. These results demonstrate the unique features of metamaterial structures that are very attractive for future high-gradient, wakefield accelerators, including two-beam and collinear accelerators. Advantages include the high shunt impedance for high power generation and high gradient acceleration; the simple and rugged structure; and a large parameter space for optimization.

Nonlocality Induced Cherenkov Threshold

“…Recently, a wealth of artificial structures including plasmonic waveguides and hyperbolic metamaterials are investigated to reduce the Cherenkov threshold. [ 28–34 ] With a proper design, effective refractive indices of eigenmodes in these structures go to infinity (i.e., ) under the classical local approximation. Consequently, Cherenkov radiation can be made threshold‐free under the local approximation, i.e., .…”

Energy loss reduction of a charge moving through an anisotropic plasma-like medium

“…Unfortunately, the latter structure possesses parasitic spatial dispersion which, however, can be suppressed [19]. In recent years, metamaterials has attracted an essential interest in the context of their implementation in particle beam physics, including wakefield generation for particle detector design [20] and modern high-gradient accelerators [21,22].…”

Radiation field of an ideal thin Gaussian bunch moving in a periodic conducting wire structure

“…This fact allows considering such sources as a new type of free electron laser-volume free electron laser [21][22][23]. Moreover, waveguides loaded with artificial metamaterials (including specific THz wire crystals) are considered nowadays as prospective candidates for the development of high-power and highgradient accelerators [24,25].…”