Ingeun Lee

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.

In situ endoscopic observation of higher-order mode conversion in a microwave mode converter based on an electro-optic probe system.

Visualizing the electromagnetic field transformation inside a microwave mode conversion region has been considered to be only realizable by simulation studies. For the first time, we present a comprehensive experimental observation of the electric field transformation occurring inside a metallic waveguide TE(01)-to-TE(02) mode converter. An efficient electro-optic (EO) probe and its associated probing system were used for measuring the electric field pattern in the external near-field region as well as in the internal and penetrated region of the mode converter. Utilizing the optically measured field patterns at the aperture of the mode converter, the conversion performance from the TE(01) mode to the TE(02) mode can be also evaluated. Experimentally measured field patterns near the apertures show excellent agreement with simulation data. The mode conversion to the next higher-order mode (TE(01) to TE(02)) was experimentally demonstrated with phase-stabilized and field-animated post processing. The presented in situ endoscopic photonic measurement technique for the field evolution inside a semi-enclosed structure could be used for visually inspecting manufacturing errors in fabricated structures, and could be of great interest for research on higher-order mode formation and transmission.

Accurate identification of whispering gallery mode patterns of gyrotron with stabilized electro-optic imaging system

The precise field pattern measurement and analysis of a typical whispering gallery mode excited in a gyrotron are important to understand the interaction physics of the gyrotron. We precisely analyzed the characteristic of a whispering gallery mode, rotating TE6,2 mode, by a photonic-assisted W-band (75–110 GHz) electro-optic imaging measurement system. The whispering gallery mode in the W-band region diverges fast in free space as it propagates from the radiation port. Therefore, scanning the field patterns of a device-under-test should be performed as close as possible to identify the devices characteristics. We successfully accomplished visualizing highly accurate field patterns of a rotating and mixed whispering gallery mode based on the measured electric field magnitude and phase by using dual optical fiber-scale electro-optic (EO) probes. We observed the distorted fields when the typical open-ended waveguide and a general EO probe were used in the extremely near-field zone, whereas a very precise f...

Design and Fabrication of a 300 GHz Modified Sine Waveguide Traveling-Wave Tube Using a Nanocomputer Numerical Control Machine

The sine waveguide slow-wave structure is a promising interaction circuit for traveling-wave tubes in the terahertz region because it possesses advantageous properties such as high transmission, easy fabrication, and elimination of the electron beam tunnel. These waveguides could be fabricated by nanocomputer numerical control (CNC) machining, a fabrication method capable of fabricating microscale components. In our study, we evaluate the practical feasibility of manufacturing 300-GHz sine waveguides with the ideal design, using nano-CNC machining. It is found that the ideal sine waveguide circuit must be modified, because of the limitations imposed by the actual tool size of the nano-CNC machine. Simulations of cold- and hot-tests of the circuit—including the electron beam effect—were conducted for both the ideal and the modified sine waveguide circuits. A modified sine waveguide was successfully machined using a nano-CNC machine with a 0.12-mm diameter tool tip. The S-parameters of the fabricated circuit were measured and compared to simulation data. A detailed analysis of the measured transmission loss was performed, and this loss was found to be attributable to a gap left by the assembly process between the two copper plates.

Design study of an energy-recirculating G-band self-driving folded waveguide traveling-wave tube

We present a design study on a self-driving folded waveguide traveling-wave tube (FWTWT). This device is an energy-recirculating hybrid vacuum tube which has a G-band FWTWT and a folded waveguide (FWG) structure backward-wave oscillator (BWO) as a self-driving source for the FWTWT. The microfabrication of the proposed circuit has been tried using a computer numerical control (CNC) machine and a super-drill. The detailed circuit simulations based on the analytic equations were compared with the CST Studios™ results, and demonstrated considerably good agreement to each other.

Precise measurement of field patterns from a TE 02 mode converter using the electro-optic probe scanning system

This paper presents electric field pattern measurements by an excellent field scanning system using a stable electro-optic (EO) field probe. It provides higher resolution and less field distortions than a metal based probe. We simulated a TE02 gyrotron mode converter by CST Microwave Studio and estimated the mode converter field pattern at 28 GHz. The field-calibrated EO sensor demonstrated up to 60 dB of Signal to Noise Ratio (SNR). Finally, we compared both results using the Cross Correlation Function (CCF). The schematic of the EO probe scanning system and estimation results are provided.

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.