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The designs of a 220 GHz folded waveguide traveling wave tube (FWTWT) have been reviewed and studied systematically via 3-D electromagnetic particle-in-cell (EM PIC) simulations. 3-D Cold test simulations using both the CFDTD and FEM methods have been carried out and compared with each other as basis for the hot test simulations. The hot test simulation results show that the gain-bandwidth features...
For higher order mode excitation in a system with a cylindrical symmetry such as a cylindrical waveguide, a higher order Bessel function is required and numerically an expansion of this function in terms of a series is mostly used. However, the accuracy of mode pattern excited is getting worse when one pushes it to higher and higher order mode with a limited number of expansion series. This inaccuracy...
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.
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