On the numerical scheme employed in gyrotron interaction simulations

Avramides, K.A.; Ram, A. K.; Dumbrājs, O.; Alberti, S.; Tran, T. M.; Kern, Stefan

doi:10.1051/epjconf/20123204017

Cited by 2 publications

(5 citation statements)

References 8 publications

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“…(3), boundary condition (4), and trajectory approach are well justified. However, in the simulated dynamic ACI cases, [13][14][15][16][17][18][19][20][21][22] the presence of two frequencies (dominant and parasitic) at the same mode leads to a beating appearing at the complex field envelope A, which broadens the spectrum of A and results in j@A/@tj/(x 0 jAj) $ 10 À1 . This weaker form of (2) may still permit the parabolic equation (3), but the validity of the simplified single-frequency boundary condition (4) and of the trajectory approach become questionable.…”

Section: Modeling Approaches and Numerical Codesmentioning

confidence: 99%

“…In order for this to be true, however, the possibility that the used PIC codes have some kind of inherent numerical dissipation that suppresses ACI in general (e.g., as discussed in Ref. 15), should be excluded. This is done in the next investigated case.…”

Section: -Mode Resonatormentioning

confidence: 99%

“…This was discussed in Ref. 15, where it was shown that COAXIAL can in fact predict dynamic ACI, provided an adequately small time step is used. Finally, the interaction code TWANG also became available to EGYC at a later stage and it also showed dynamic ACI, in agreement with the other codes.…”

Section: Introductionmentioning

confidence: 99%

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

Avramidis

Ioannidis

Kern³

et al. 2015

Phys. Plasmas

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Experimental observation of the effect of aftercavity interaction in a depressed collector gyrotron oscillatorThere are cases where gyrotron interaction simulations predict dynamic After-Cavity Interaction (ACI). In dynamic ACI, a mode is excited by the electron beam at a dominant frequency in the gyrotron cavity and, at the same time, this mode is also interacting with the beam at a different frequency in the non-linear uptaper after the cavity. In favor of dynamic ACI being a real physical effect, there are some experimental findings that could be attributed to it, as well as some physical rationale indicating the possibility of a mode being resonant with the beam at different frequencies in different regions. However, the interaction codes used in dynamic ACI prediction up to now are based on simplifications that put questions on their capability of correctly simulating this effect. In this work, the shortcomings of the usual simplifications with respect to dynamic ACI modeling, namely, the trajectory approach and the single-frequency boundary condition, are identified. Extensive simulations of dynamic ACI cases are presented, using several "in-house" as well as commercial codes. We report on the comparison and the assessment of different modeling approaches and their results and we discuss whether, in some cases, dynamic ACI can be a numerical artifact or not. Although the possibility of existence of dynamic ACI in gyrotrons is not disputed, it is concluded that the widely used trajectory approach for gyrotron interaction modeling is questionable for simulating dynamic ACI and can lead to misleading results.

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Section: Modeling Approaches and Numerical Codesmentioning

confidence: 99%

Section: -Mode Resonatormentioning

confidence: 99%

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

Avramidis

Ioannidis

Kern³

et al. 2015

Phys. Plasmas

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“…approximately 0.5-1 % as shown in [1,2] and references therein. The proper description of the wave-particle interaction in the commonly used gyro-averaged slow time scale models [3][4][5] requires to properly define the radiation boundary conditions at the extremities of the considered interaction space. Compared to the seminal paper by Ginzburg et al [6], in which the non-reflecting frequency-independent boundary condition was derived and used in the case of a simplified interaction space with constant radius, in this paper, the interaction space is extended such to include the real gyrotron cavity as well as the uptaper and a simplified launcher following the cavity.…”

mentioning

confidence: 99%

“…Fig 4. The reflection coefficient R(Ω) in the vicinity of Ω 1 = (ω 1 − ω 0 )/ω 0 = −0.06 for different time steps ω 0 Δt and k ⊥ /k 0 = 0.9…”

mentioning

confidence: 99%

Generalized Radiation Boundary Conditions in Gyrotron Oscillator Modeling

Alberti

Tran

Brunner

et al. 2015

J Infrared Milli Terahz Waves

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A numerical procedure to implement a frequency-independent generalized non-reflecting radiation boundary conditions, GNRBC, based on the Laplace Transform, is described in details and tested successfully on a simple 2 frequency test problem. In the case of non-stationary regimes occurring in gyrotron oscillators, it is shown that the reflection at frequencies significantly separated from the carrier frequency can be effectively suppressed by this method. A detailed analysis shows that this numerical approach can be consistently used only for models in which there is no assumed separation of time scales between the RF field envelope timeevolution and the electron time of flight across the interaction region. The GNRBC has been implemented in a nonlinear time-dependent self-consistent monomode model, TWANGpic, in which there is no time scale separation since the RF field envelope is updated at each integration time step of the electron motion. The illustration of the effectiveness of the GNRBC is made with TWANGpic on a gyrotron for which extensive theoretical and experimental results have been performed.

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On the numerical scheme employed in gyrotron interaction simulations

Cited by 2 publications

References 8 publications

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

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

Generalized Radiation Boundary Conditions in Gyrotron Oscillator Modeling

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