Sung Gug Kim

Observation of trapped-modes excited in double-layered symmetric electric ring resonators

We report on experimental observations of trapped-mode resonances in double-layered symmetric electric ring resonators separated by dielectric inserts. The resulting metamaterial introduces trapped-mode resonances that were thought to be produced only by asymmetric metamaterial unit cells. Experimental verification of the newly observed trapped modes, along with the analysis of the stacked metamaterial geometry reported in this paper, opens an alternative way of forming sharp resonances in a symmetric metamaterial structure extended in all three dimensions.

Direct Real-Time Power Measurement of a High-Power Electron Cyclotron Maser by a Simple One-Point Schottky Detector Signal

Measurements of the absolute power of high-power millimeter/THz wave generators have been considered to be highly variable and to occasionally produce faulty results owing to experimental difficulty. In this study, we propose a calibration-free method for real-time power measurement of an electron cyclotron maser system, a so-called gyrotron. We demonstrate the feasibility of the method by using a recently developed W-band gyrotron with a peak power of tens of kilowatts. The technique is based on transmitter antenna power measurement by using the Friis transmission equation with a defined gyrotron antenna gain. The new technique will allow extremely simple and accurate real-time measurement of output power over a wide dynamic range ( dB) for continuous wave sources to high-power millimeter/THz wave sources with nanosecond pulse lengths.

Remote Detection of Radioactive Material using High-Power Pulsed Electromagnetic Radiation

Remote detection of radioactive materials is impossible when the measurement location is far from the radioactive source such that the leakage of high-energy photons or electrons from the source cannot be measured. Current technologies are less effective in this respect because they only allow the detection at distances to which the high-energy photons or electrons can reach the detector. Here we demonstrate an experimental method for remote detection of radioactive materials by inducing plasma breakdown with the high-power pulsed electromagnetic waves. Measurements of the plasma formation time and its dispersion lead to enhanced detection sensitivity compared to the theoretically predicted one based only on the plasma on and off phenomena. We show that lower power of the incident electromagnetic wave is sufficient for plasma breakdown in atmospheric-pressure air and the elimination of the statistical distribution is possible in the presence of radioactive material.

Validation of 3-D Time Domain Particle-in-Cell Simulations for Cold Testing a W-Band Gyrotron Cavity

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.

Study on statistical breakdown delay time in argon gas using a W-band millimeter-wave gyrotron

In this study, we investigated plasma initiation delay times for argon volume breakdown at the W-band frequency regime. The threshold electric field is defined as the minimum electric field amplitude needed for plasma breakdown at various pressures. The measured statistical delay time showed an excellent agreement with the theoretical Gaussian distribution and the theoretically estimated formative delay time. Also, we demonstrated that the normalized effective electric field as a function of the product of pressure and formative time shows an outstanding agreement to that of 1D particle-in-cell simulation coupled with a Monte Carlo collision model [H. C. Kim and J. P. Verboncoeur, Phys. Plasmas 13, 123506 (2006)].

Frequency splitting of a multi-layered electric ring resonator

We present experimental results on the multilayering effects of an electric ring resonator. The electromagnetic response of the electric ring resonator is measured via a scattering matrix using a vector network analyzer at the X-band frequency. Structures of the electric ring resonator with up to four layers were tested and analyzed using commercial software. We demonstrate that, in an electric ring resonator, the electric and magnetic dipole polarization effect gives rise to resonance frequency splitting when the cell is multilayered.

Feasibility study on performance test of a quasi-optical mode converter using a linear, simple higher order mode generator

In this paper, we introduce a new test scheme to verify the design of a quasi-optical internal mode converter. A simple, novel higher order mode generator has been designed and used for the cold-test of the quasi-optical mode converter. The mode generator excites a linearly polarized TE6,2 mode. The paper demonstrates that the new cold-test scheme using the linear mode generator is proven to be an excellent method for the performance check of a designed quasi-optical mode converter.

Design study of MIG for dual-band gyrotron

The paper presents the design study of a diode type Magnetron Injection Gun (MIG) operating at W-band and Y-band. The design study has been done by two different simulation codes, EGUN code and CST Particle studio. We will present crucial design parameters for optimizing geometry of MIG and the simulation results with respect to dual band.

Sensing a radioactive material remotely using a high power THz gyrotron

Recent progress in vacuum electronics based high power THz source allows realization of technically unreachable regime in human society. In this talk, I present detecting scheme on remotely present radioactive material using a high power THz source.