Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

Othman, Mohamed A. K.; Veysi, Mehdi; Figotin, Alexander; Capolino, Filippo

doi:10.1063/1.4942791

Cited by 43 publications

(72 citation statements)

References 49 publications

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“…[10][11][12][13][14][15][16][17][18] However, a very few experiments have been carried out to actually generate high power microwaves with an electron beam passing through an MTM structure. [19][20][21][22][23] At MIT, in our previous experiment, 19 we built a structure with two MTM plates loaded in a waveguide with dimensions below the cut-off of the TM 11 mode.…”

Section: Introductionmentioning

confidence: 99%

High power long pulse microwave generation from a metamaterial structure with reverse symmetry

Stephens

Mastovsky

et al. 2018

Physics of Plasmas

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Experimental operation of a high power microwave source with a metamaterial (MTM) structure is reported at power levels to 2.9 MW at 2.4 GHz in full 1 μs pulses. The MTM structure is formed by a waveguide that is below cutoff for TM modes. The waveguide is loaded by two axial copper plates machined with complementary split ring resonators, allowing two backward wave modes to propagate in the S-Band. A pulsed electron beam of up to 490 kV, 84 A travels down the center of the waveguide, midway between the plates. The electron beam is generated by a Pierce gun and is focused by a lens into a solenoidal magnetic field. The MTM plates are mechanically identical but are placed in the waveguide with reverse symmetry. Theory indicates that both Cherenkov and Cherenkov-cyclotron beam-wave interactions can occur. High power microwave generation was studied by varying the operating parameters over a wide range, including the electron beam voltage, the lens magnetic field, and the solenoidal field. Frequency tuning with a magnetic field and beam voltage was studied to discriminate between operation in the Cherenkov mode and the Cherenkov-cyclotron mode. Both modes were observed, but pulses above 1 MW of output power were only seen in the Cherenkov-cyclotron mode. A pair of steering coils was installed prior to the interaction space to initiate the cyclotron motion of the electron beam and thus encourage the Cherenkov-cyclotron high power mode. This successfully increased the output power from 2.5 MW to 2.9 MW (450 kV, 74 A, 9% efficiency).

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Section: Introductionmentioning

confidence: 99%

High power long pulse microwave generation from a metamaterial structure with reverse symmetry

Stephens

Mastovsky

et al. 2018

Physics of Plasmas

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“…Furthermore, applications featuring slow-light properties associated with the DBE has been proposed such as small/directive antennas [12], [20]- [23], lowthreshold switching [10], [13], pulse compression [24], and filters [11]. The theory of four mode degeneracy was furthermore utilized for the first time to show giant gain enhancement [10] in slow-wave structures with DBE, for high power amplifiers [17] and oscillators [18], [25], when interacting with an electron beam. Since DBE involves four degenerate modes, it requires sophisticated theoretical framework to reveal its unique properties; such as coupled transmission line theory developed in [3], [6], with a nondiagonalizable system matrix.…”

Section: Introductionmentioning

confidence: 99%

Experimental Demonstration of Degenerate Band Edge in Metallic Periodically Loaded Circular Waveguide

Othman¹,

Pan

Atmatzakis

et al. 2017

IEEE Trans. Microwave Theory Techn.

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Abstract-We experimentally demonstrate for the first time the degenerate band edge (DBE) condition, namely the degeneracy of four Bloch modes, in loaded circular metallic waveguides. The four modes forming the DBE represent a degeneracy of fourth order occurring in a periodic structure where four Bloch modes, two propagating and two evanescent, coalesce. It leads to a very flat wavenumber-frequency dispersion relation, and the finitelength structure's quality factor scales as N 5 where N is the number of unit cells. The proposed waveguide in which DBE is observed here is designed by periodically loading a circular waveguide with misaligned elliptical metallic rings, supported by a low-index dielectric. We validate the existence of the DBE in such structure using measurements and we report good agreement between full-wave simulation and the measured response of the waveguide near the DBE frequency; taking into account metallic losses. We correlate our finding to theoretical and simulation results utilizing various techniques including dispersion synthesis, as well as observing how quality factor and group delay scale as the structure length increases. Moreover, the reported geometry is only an example of metallic waveguide with DBE: DBE and its characteristics can also be designed in many other kinds of waveguides and various applications can be contemplated as high microwave generation in amplifiers and oscillators based on an electron beam interaction or solid state devices, pulse compressors and microwave sensors.Index Terms-Degenerate band edge (DBE), slow-wave structures, cavity resonators.

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“…At a fourth-order EPD, the transfer matrix becomes similar to a four-dimensional Jordan matrix, nde nd e nd e [22,70]. Similar to the second-order EPD, the wavenumber near a fourth-order EPD asymptotically follows the fractional power expansion…”

Section: I)mentioning

confidence: 83%

“…Note that the homogenous solutions of (3) are constructed from the four eigenvectors in (7) in the case where the matrix T can be diagonalized. When T is not diagonalizable, i.e., at an EPD, generalized eigenvectors are used instead of the regular eigenvectors in (7) [22]. The four eigenvalues of (7) are determined from…”

Section: A State Vector Evolution and Transfer Matrixmentioning

confidence: 99%

“…In particular, the "frozen-wave" regime associated with the DBE condition [5,12,16,[18][19][20][21][22] has been demonstrated to provide a better localization of light through large enhancement of the local density of states, as well as enhancement of gain in active configurations [16,22]. Moreover, several DBE implementations have been carried out in coupled silicon waveguides [15,21] or 2D photonic crystals [23], with potential applications to lasers [14,16], and more recently at microwaves [24], for low-threshold oscillations [25][26][27] and efficient high power generation [22,25,28].…”

Section: Introductionmentioning

confidence: 99%

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Exceptional points of degeneracy andPTsymmetry in photonic coupled chains of scatterers

2017

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We demonstrate the existence of exceptional points of degeneracy (EPDs) of periodic eigenstates in nonHermitian coupled chains of dipolar scatterers. Guided modes supported by these structures can exhibit an EPD in their dispersion diagram at which two or more Bloch eigenstates coalesce, in both their eigenvectors and eigenvalues. We show the emergence of a second-order modal EPD associated with the parity-time (PT) symmetry condition, at which each particle pair in the double chain exhibits balanced gain and loss. Furthermore, we also demonstrate a fourth-order EPD occurring at the band edge. Such degeneracy condition was previously referred to as a degenerate band edge in lossless anisotropic photonic crystals. Here, we rigorously show it under the occurrence of gain and loss balance for a discrete guiding system. We identify a more general regime of gain and loss balance showing that PT-symmetry is not necessary to attain EPDs. Moreover, we investigate the degree of detuning of the EPD when the geometrical symmetry or balanced condition is broken. Furthermore, we demonstrate a realistic implementation of the EPD in a coupled chain made of pairs of plasmonic nanospheres and active core-shell nanospheres at optical frequencies. These findings open unprecedented avenues toward superior light localization and transport with application to high-Q resonators utilized in sensors, filters, low-threshold switching and lasing.

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Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

Cited by 43 publications

References 49 publications

High power long pulse microwave generation from a metamaterial structure with reverse symmetry

High power long pulse microwave generation from a metamaterial structure with reverse symmetry

Experimental Demonstration of Degenerate Band Edge in Metallic Periodically Loaded Circular Waveguide

Exceptional points of degeneracy andPTsymmetry in photonic coupled chains of scatterers

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