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Sawant, Ashwini,Yu, Dongho,Kim, Dongsung,Choe, Mun Seok,Choi, EunMi IEEE 2017 IEEE transactions on terahertz science and technol Vol.7 No.2
<P>We present a phase coefficient optimization technique for determining the vortex charge of a high-power orbital angular momentum beam. This high-power vortex beam is generated by transmitting a Gaussian-like beam emitted by a gyrotron with an output power of 25 kW through a spiral phase plate (SPP), which introduces a vorticity at the center of the beam characterized by the geometrical parameters of the SPP. One rigorous, intensity-measurement-based, phase retrieval technique, known as the Gerchberg-Saxton algorithm, does not converge to a correct solution because of the presence of a phase singularity in the high-power vortex beam. Here, we introduce a new phase retrieval algorithm that chooses an appropriate initial phase estimate. This technique yields successful vortex charge determination for both low- and high-power vortex beams. The retrieved intensity profiles show 99.51% and 99.27% intensity regeneration at measurement planes with optimized initial phase estimates for the low- and high-power beams, respectively.</P>
Development of the Full Package of Gyrotron Simulation Code
Ashwini Sawant,EunMi Choi 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.11
A complete code-package for gyrotron simulation to analyze its performance is under development in UNIST, Korea. We first time report the present status of the code-package named as UNIST Gyrotron Design Tool (UGDT). It can perform design simulations for gyrotron's interaction cavity, RF window, and the essential mode calculations including the study of mode competition. We will discuss about its salient features, theory, numerical implementation, and its calculation result for 95 GHz UNIST Gyrotron. Moreover, we will validate its capability to perform the mode competition calculation for fundamental and second harmonic modes.
Sawant, Ashwini,Sung Gug Kim,Ming-Chieh Lin,Jung Ho Kim,Yongjun Hong,Joonho So,EunMi Choi IEEE 2014 IEEE transactions on plasma science Vol.42 No.12
<P>This paper evaluates the performance and reliability of a commercially available 3-D conformal finite-difference time-domain particle-in-cell (PIC) code, VSim, for cold test simulations of a gyrotron cavity. An interaction cavity for a 95-GHz gyrotron is simulated and optimized using the VSim PIC code to achieve TE6,2 mode excitation. The optimized cavity design is also studied and compared using the commercially available numerical code, CASCADE, and PIC code, MAGIC. A rigorous analysis of the simulation results obtained through VSim and MAGIC is performed using the CASCADE results as a reference. The performance of VSim is also compared with MAGIC based on its accuracy for calculating the resonant frequency and quality factor. Finally, the optimized cavity is fabricated and experimentally tested to measure the resonant frequency and the quality factor. The experimental results confirm the reliability and accuracy of the VSim cold cavity results.</P>