A comparative study on the modeling of dynamic after-cavity interaction in gyrotrons

Avramidis, Konstantinos A.; Ioannidis, Zisis C.; Kern, Stefan; Samartsev, A.; Pagonakis, I.; Tigelis, I. G.; Jelonnek, John

doi:10.1063/1.4919924

Cited by 18 publications

(9 citation statements)

References 22 publications

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“…Note that a typical time of variations in the field axial structure (about 5-10 ns) is much greater than the electron transit time through the resonator (about 0.1 ns). Therefore, the assumption about the smallness of the electron transit time in comparison with the cavity fill time used in MAGY as well as in many other codes is valid in our case and, correspondingly, there is no reason to take into account field modifications during the electron transit time, which were considered in [37][38][39][40].…”

Section: Discussionmentioning

confidence: 95%

Field Formation in the Interaction Space of Gyrotrons

Nusinovich

Dumbrājs

2015

J Infrared Milli Terahz Waves

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For gyrotron applications in plasma installations, one of the most important factors is the gyrotron efficiency. To maximize the interaction efficiency, it is necessary not only to optimize such operating parameters as the magnetic field, beam voltage, and current but also the axial profile of the electromagnetic (EM) field in the interaction space. The present paper describes a study of the effect of the profile of an irregular waveguide serving as a resonator on the axial structure of the EM field. Specific attention is paid to the profile of the uptaper connecting the regular part of a resonator to the output waveguide. Conditions of applicability of the nonuniform string equation, which is widely used in gyrotron designs for finding the axial structure of the EM field, are discussed. Also discussed are the occurrence of reflections from a smooth uptaper and the analogy between the nonuniform string equation and the stationary Schrodinger equation.

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Section: Discussionmentioning

confidence: 95%

Field Formation in the Interaction Space of Gyrotrons

Nusinovich

Dumbrājs

2015

J Infrared Milli Terahz Waves

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“…On this gyrotron, nanosecond-pulses were observed, [22][23][24] which result in a very strong and fast variation of the field-profile. Another situation, in which the model of TWANG is no longer valid is in the case of dynamic After-Cavity-Interaction (ACI), [25][26][27] for which there are weak and unclear experimental evidences. 28 In order to be able to simulate these situations realistically, one has to relax the above-mentioned approximation.…”

Section: Code Description and Modelmentioning

confidence: 99%

“…Dynamic ACI has been predicted by different codes based on similar models as the one implemented in TWANG. [25][26][27] In these cases, a parasitic interaction, often with the same transverse mode, is predicted by trajectory-like codes as TWANG in the far uptaper-region or launcher region behind the cavity. The ACI-frequency is of the order of 5%-10% below the main frequency, close to the cutoff-frequency in the uptaper region, where the ACIoscillation is excited.…”

Section: -5mentioning

confidence: 99%

TWANG-PIC, a novel gyro-averaged one-dimensional particle-in-cell code for interpretation of gyrotron experiments

et al. 2015

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International audienceA new gyrotron simulation code for simulating the beam-wave interaction using a monomode time-dependent self-consistent model is presented. The new code TWANG-PIC is derived from the trajectory-based code TWANG by describing the electron motion in a gyro-averaged one-dimensional Particle-In-Cell (PIC) approach. In comparison to common PIC-codes, it is distinguished by its computation speed, which makes its use in parameter scans and in experiment interpretation possible. A benchmark of the new code is presented as well as a comparative study between the two codes. This study shows that the inclusion of a time-dependence in the electron equations, as it is the case in the PIC-approach, is mandatory for simulating any kind of non-stationary oscillations in gyrotrons. Finally, the new code is compared with experimental results and some implications of the violated model assumptions in the TWANG code are disclosed for a gyrotron experiment in which non-stationary regimes have been observed and for a critical case that is of interest in high power gyrotron development

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“…3]). The Fourier transform of (4) yields (8) The term comes from the normalization of the Fourier transform used in this paper; more details can be found in the Appendix. The spatial derivative of (8) is (9) Assuming that uniform waveguides are attached at the ends of the gyrotron cavity (i.e., at the ends of the simulated interaction region), we can substitute (9) and (8) into (2).…”

Section: A General Boundary Conditionmentioning

confidence: 99%

“…1) It has been already observed from numerical simulations, that nonstationary dynamic after-cavity-interaction (ACI) may cause the appearance of other frequencies [7], [8]. Furthermore, there are frequencies measured from the experiment using the system in [9], which are suspected to be the spectral lines caused by ACIs [10].…”

Section: Introductionmentioning

confidence: 99%

An Improved Broadband Boundary Condition for the RF Field in Gyrotron Interaction Modeling

Avramidis

Thumm

et al. 2015

IEEE Trans. Microwave Theory Techn.

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Gyrotrons are the only RF sources providing significantly high output powers at continuous-wave operation in the sub-terahertz frequency range. A prerequisite for a proper study of gyrotron behavior is the accurate time-dependent self-consistent simulation of the interaction between the electron beam and the RF wave inside the interaction region (cavity). That requires an accurate description of the RF fields at the boundaries of the interaction region. In this work, an improved broadband boundary condition is proposed. Based on polynomial series expansion of the load impedance and of the wavenumber, this boundary condition not only features a significantly improved broadband matching, but also allows a customizable frequency-dependent reflection coefficient at the boundaries. The boundary condition has a general formulation, i.e., it does not rely on a special numerical method. For the case of perfect matching, the new formulation is validated through comparing the numerically calculated reflection coefficients with those obtained by the state-of-the-art matched gyrotron broadband boundary condition, whereas the validation in the case of a given frequency-dependent reflection is done by comparing the numerically calculated reflection with the prescribed one. Although this concept is initially intended for the simulation of gyrotron cavities, it can be easily extended to any other open-cavity resonators, for which proper definition of the boundary conditions is required.

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A comparative study on the modeling of dynamic after-cavity interaction in gyrotrons

Cited by 18 publications

References 22 publications

Field Formation in the Interaction Space of Gyrotrons

Field Formation in the Interaction Space of Gyrotrons

TWANG-PIC, a novel gyro-averaged one-dimensional particle-in-cell code for interpretation of gyrotron experiments

An Improved Broadband Boundary Condition for the RF Field in Gyrotron Interaction Modeling

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