VitzroTech

Ansan, South Korea

VitzroTech

Ansan, South Korea
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Jung Y.,RISP | Joung M.,RISP | Lee M.,RISP | Lee J.,Vitzrotech | Seo J.,Vitzrotech
IPAC 2016 - Proceedings of the 7th International Particle Accelerator Conference | Year: 2016

Either organic or inorganic residues on the inner surface of the superconducting cavity can cause serious problems during the cavity operation. High pressure rinsing experiments was carried out to check out how a prototype HPR machine removes defects. HPR experiments were performed with a simplified cavity structure, and analyzed as a function of the pressure, the distance from a nozzle, and the sizes of defects on the niobium surface. In this presentation, we will discuss the performance of the prototype HPR machine. Copyright © 2016 CC-BY-3.0 and by the respective authors.


Joo Y.,Pohang Accelerator Laboratory | Kim S.-H.,Pohang Accelerator Laboratory | Hwang W.,Pohang Accelerator Laboratory | Ryu J.,VitzroTech | Roh S.,VitzroTech
Journal of the Korean Physical Society | Year: 2016

A new RF window is designed for high-power operation at the Pohang Light Source-II (PLSII) S-band linear accelerator (LINAC) RF system. In order to reduce the strength of the electric field component perpendicular to the ceramic disk, which is commonly known as the main cause of most discharge breakdowns in ceramic disk, we replace the pill-box type cavity in the conventional RF window with an overmoded cavity. The overmoded cavity is coupled with input and output waveguides through dual side-wall coupling irises to reduce the electric field strength at the iris and the number of possible mode competitions. The finite-difference time-domain (FDTD) simulation, CST MWS, was used in the design process. The simulated maximum electric field component perpendicular to the ceramic for the new RF window is reduced by an order of magnitude compared with taht for the conventional RF window, which holds promise for stable high-power operation. © 2016, The Korean Physical Society.


Joo Y.,Pohang Accelerator Laboratory | Park Y.,Pohang Accelerator Laboratory | Heo H.,Pohang Accelerator Laboratory | Heo J.,Pohang Accelerator Laboratory | And 7 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2017

In order to achieve beam acceleration to the beam energy of 10 GeV at the end of its 716 m-long linear accelerator (Linac), the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) is going to operate the Stanford Linear Accelerator Energy Doubler (SLED) at the maximum klystron output peak power of 80 MW, with a pulse length of 4 μs, and at a repetition rate of 60 Hz. The original SLED that had been used in Pohang Light Source-II (PLS-II) can no longer sustain such a high-power operation because excessive radiation caused by RF breakdown has been frequently detected even at the lower klystron peak power during the PLS-II operation. Therefore, a new SLED is designed by modifying both the 3-dB power hybrid and the waveguide-cavity coupling structure of the original SLED where the excessive radiation has been mainly detected. The finite-difference time-domain (FDTD) simulation in the CST Microwave Studio shows that the new SLED has a peak electric field and a surface current lower than those of the original SLED at the same level of the RF input peak power, which would secure stable high-power operation. All of the 42 SLEDs in the PAL-XFEL Linac are newly fabricated and installed. During the RF conditioning of the PAL-XFEL Linac, no significant vacuum and radiation issue was found in the new SLEDs. Finally, the accelerated electron beam energy of 10 GeV obtained at the end of the PAL-XFEL Linac verified that the RF performance of the new SLED is stable. © 2016 Elsevier B.V.


Joo Y.,Pohang Accelerator Laboratory | Lee B.-J.,Pohang Accelerator Laboratory | Kim S.-H.,Pohang Accelerator Laboratory | Kong H.-S.,Pohang Accelerator Laboratory | And 3 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2017

For stable high-power operation, a new RF window is developed in the S-band linear accelerator (Linac) RF systems of the Pohang Light Source-II (PLS-II) and the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL). The new RF window is designed to mitigate the strength of the electric field at the ceramic disk and also at the waveguide-cavity coupling structure of the conventional RF window. By replacing the pill-box type cavity in the conventional RF window with an overmoded cavity, the electric field component perpendicular to the ceramic disk that caused most of the multipacting breakdowns in the ceramic disk was reduced by an order of magnitude. The reduced electric field at the ceramic disk eliminated the Ti–N coating process on the ceramic surface in the fabrication procedure of the new RF window, preventing the incomplete coating from spoiling the RF transmission and lowering the fabrication cost. The overmoded cavity was coupled with input and output waveguides through dual side-wall coupling irises to reduce the electric field strength at the waveguide-cavity coupling structure and the possibility of mode competitions in the overmoded cavity. A prototype of the new RF window was fabricated and fully tested with the Klystron peak input power, pulse duration and pulse repetition rate of 75 MW, 4.5 μs and 10 Hz, respectively, at the high-power test stand. The first mass-produced new RF window installed in the PLS-II Linac is running in normal operation mode. No fault is reported to date. Plans are being made to install the new RF window to all S-band accelerator RF modules of the PLS-II and PAL-XFEL Linacs. This new RF window may be applied to the output windows of S-band power sources like Klystron as wells as the waveguide windows of accelerator facilities which operate in S-band. © 2017 Elsevier B.V.


Heo H.,Pohang University of Science and Technology | Joo Y.-D.,Pohang University of Science and Technology | Park Y.-J.,Pohang University of Science and Technology | Kang H.-S.,Pohang University of Science and Technology | And 4 more authors.
Journal of the Korean Physical Society | Year: 2015

We developed an S-band traveling-wave accelerating structure for the Pohang Accelerator Laboratory’s X-ray free-electron laser (PAL-XFEL), and we fabricated and tested a full-scale prototype. In order to reduce the field asymmetry inside the coupler cavity, we used the SUPERFISH code and the CST MWS electromagnetic field solvers to design the constant-gradient traveling-wave accelerator to use quasi-symmetric single-feed racetrack couplers. The RF measurement results indicate that the accelerating gradient of the prototype structure is as high as 27 MV/m for an input RF power of 65 MW. © 2015, The Korean Physical Society.


Joo Y.,Pohang Accelerator Laboratory | Park Y.,Pohang Accelerator Laboratory | Heo H.,Pohang Accelerator Laboratory | Hu J.,Pohang Accelerator Laboratory | And 8 more authors.
Journal of the Korean Physical Society | Year: 2014

The 3-dB power splitter to be used in the Pohang Accelerator Laboratory X-ay Free-electron Laser (PAL XFEL), which have been under construction since 2011, must operate at a peak power of 400 MW and a repetition rate of 120 Hz. For these operational conditions of the PAL XFEL, the old 3-dB power splitter that was originally designed to be used in the PLS LINAC will most suffer from RF breakdown. Therefore, for the new 3-dB power splitter, the original design has been modified to reduce the field gradient and the surface current. The new 3-dB power splitter is designed by using a finite-difference time-domain (FDTD) simulation. We have fabricated a prototype, and the result of a high-power test indicates that the RF performance of the new 3-dB power splitter satisfies the specifications of the PAL XFEL S-band LINAC RF system. © 2014 The Korean Physical Society.


Joo Y.,Pohang Accelerator Laboratory | Park Y.,Pohang Accelerator Laboratory | Heo H.,Pohang Accelerator Laboratory | Hu J.,Pohang Accelerator Laboratory | And 8 more authors.
Journal of the Korean Physical Society | Year: 2013

The directional coupler to be used in the Pohang Accelerator Laboratory X-ray free electron laser (PAL XFEL) under construction since 2011 must satisfy the conditions for operating at a peak power of 400 MW and a repetition rate of 120 Hz. In these operational conditions of the PAL XFEL, the old Bethe-hole directional coupler that was originally designed to be used in the Pohang Light Source linac is more likely to inflict damages on the ceramic window that cause vacuum leaks. Therefore, for the new Bethe-hole directional coupler, the original design has been modified to use a conventional N-type RF vacuum feedthrough for vacuum sealing instead of the ceramic window. The new Bethe-hole directional coupler is designed by using a finite-difference time-domain simulation. We have fabricated a prototype, and the result of a high-power test indicates that the RF performance of the new DC satisfies the specifications of the PAL XFEL S-band Linac RF system. © 2013 The Korean Physical Society.


Park D.,Korea Advanced Institute of Science and Technology | Heo S.,Korea Advanced Institute of Science and Technology | Cho H.,VITZROTECH | Kwon S.,Korea Advanced Institute of Science and Technology
Transactions of the Japan Society for Aeronautical and Space Sciences | Year: 2015

A gas-turbine-driven pump system was designed and tested. Pump systems are generally driven by an electric motor, but a gas turbine is occasionally used as the power source for high power and performance; for example, the turbopump of a liquid rocket propulsion system. For research on turbopumps, a gas generator, turbine, and pump are developed. After each component is developed, the performance should be confirmed with a link test. In the case of a turbopump, an axial turbine is applied to generate huge torque, but a radial inflow turbine was used in this research. A radial inflow turbine can be obtained easily and mass-produced. System analysis was conducted using a link test with all components at once. The turbine generated shaft power under steady operation of the gas generator, and the pump performance was measured using a stepped closing valve at the pump exit. Turbine heat loss was considered and a slip factor was applied to the impeller design to modify performance. This research shows the feasibility of developing a pump system operated by a radial inflow turbine and its application to a small turbopump for a hybrid rocket propulsion system and an air-independent system. © 2015 The Japan Society for Aeronautical and Space Sciences.


Kang H.-G.,VITZROTECH | Song U.-S.,VITZROTECH | Kim J.-H.,VITZROTECH | Kim S.-C.,VITZROTECH | And 2 more authors.
Journal of Electrical Engineering and Technology | Year: 2014

The digital substations are being built based on the IEC 61850 network. The cooperation and protection of power system are becoming more intelligent and reliable in the environment of digital substation. This paper proposes a novel method to prevent the malfunction caused by the Transformer Magnetizing Inrush Current(TMIC) using the IEC 61850 based data sharing between the IEDs. To protect a main transformer, the current differential protection(87T) and over-current protection(50/51) are used generally. The 87T IED applies to the second harmonic blocking method to prevent the malfunction caused by the TMIC. However, the 50/51 IED may malfunction caused by the TMIC. To solve that problem, the proposed method uses a GOOSE inter-lock signal between two IEDs. The 87T IED transmits a blocking GOOSE signal to the 50/51 IED, when the TMIC is detected. The proposed method can make a cooperation of digital substation protection system more intelligent. To verify the performance of proposed method, this paper performs the real time test using the RTDS (Real Time Digital Simulator) test-bed. Using the RTDS, the power system transients are simulated, and the TMIC is generated. The performance of proposed method is verified in real-time using that actual current signals. The reaction of simulated power system responding to the operation of IEDs can be also confirmed.

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