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We have found an improved form of a Bessel function for accurate and efficient numerical computation. This approximation is good for used in studying a higher order mode in a cylindrical system such as an overmoded waveguide or a fusion gyrotron cavity. The approximated solution is a fine tuned combination of a series expansion and an asymptotic form.
We have performed a detailed benchmark of a conformal finite difference time domain (CFDTD) method for applications in fusion gyrotron study. The accuracy and efficiency of simulations are the main concerns as a fusion gyrotron cavity is a computationally large scale model. Therefore, the validation of a simulation method is important for us to adopt it for the future study. Here we use a simple circular...
Modeling a gyrotron cavity in 3D and timedomain is very challenging due to the open-end features of cavity structure and higher-order mode excitation employed to achieve high efficiency. In this work, a conformal finite-difference time-domain (CFDTD) method is proposed to simulate a gyrotron cavity and a particle-in-cell (PIC) algorithm is used to describe a gyro electron beam. Our preliminary result...
Low frequency oscillations (LFOs) have been obtained in a 3D time domain simulation for the first time. From our preliminary simulation studies, it is found that not only magnetic compression profile but initial velocity or velocity ratio play an important role in the operation of a MIG electron gun. In addition, the secondary emission effects on the LFOs are also studied. The frequency of LFOs has...
Low frequency oscillations (LFOs) have been obtained in a 3D time domain simulation for the first time. From our preliminary simulation studies, it is found that not only magnetic compression profile but initial velocity or velocity ratio play an important role in the operation of a MIG electron gun. In addition, the secondary emission effects on the LFOs are also studied. The frequency of LFOs has...
Low-frequency oscillations (LFOs) have been observed in a high average power gyrotron and the trapped electron population contributing to the oscillation has been measured. However, understanding of the LFOs remains incomplete and a full picture of this parasitic phenomenon has not been seen yet. In this work, we use a 3D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) method...
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