Simulation Of Traveling-wave Tubes Research Articles

有限电导率模块在THz折叠波导行波管模拟中的验证和确认

有限电导率模块在THz折叠波导行波管模拟中的验证和确认

Accurate Representation of Attenuation in Helix TWT Simulation Codes

We report on the results of a study that compares an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hoc</i> model of circuit attenuation used in helix traveling-wave tube (TWT) simulation codes with the exact small-signal theory of a beam interacting with a slow wave supported by a sheath helix in the presence of loss in order to ascertain whether attenuation is treated with sufficient accuracy by the model used in those codes. This study was motivated in part by the fact that losses in both dielectrics and metals generally increase with increasing operating frequency, making the accuracy of the model a potential concern for millimeter-wave helix TWT design. Our basic conclusion is that the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hoc</i> model is sufficiently accurate for attenuation rates up to a few decibels per pitch in cases that we have studied. For much larger attenuation rates, as may occur in a sever region, accuracy can be improved by taking into account the (quadratic) dependence of the cold circuit phase velocity on the attenuation rate.

Three-Dimensional Modeling of AC Space Charge for Large-Signal TWT Simulation

We describe a new model for calculating the ac space charge in a linear-beam traveling wave tube (TWT) large-signal simulation code when the true three-dimensional (3-D) geometry of the interaction circuit is taken into account. We use the 3-D electromagnetic simulation code CTLSS to characterize the ac space charge fields generated by a set of test currents placed inside the periodic interaction structure. This information, expressed in matrix form, is used by the large-signal simulation codes CHRISTINE-1D and CHRISTINE-3D to compute self-consistently the additional space charge field terms due to the structure in response to the beam evolution during the simulation. We present the formulation, and describe the implementation in both CTLSS and the large-signal codes. We validate the model by comparison with the analytical sheath helix model, and evaluate the importance of including this correction for modeling a number of helix and coupled-cavity TWT devices.