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A New RF Window Designed for High-Power Operation in an S-band LINAC RF System
Youngdo Joo,Seung-Hwan Kim,Woonha Hwang,Jiwan Ryu,Sungjoo Roh 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.6
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.
Formation and Annealing Effect of Tolanethioacetate Self-Assembled Monolayers on Au(111)
Youngdo Jeong,한진욱,Nakjoong Kim,Youngil Lee,이창진,Masahiko Hara,노재근 대한화학회 2007 Bulletin of the Korean Chemical Society Vol.28 No.12
Self-assembled monolayers (SAMs) were formed by adsorption of thioacetyl-terminated tolanethioacetate (TTA) on Au(111) in a 0.5-mM ethanol solution after one day immersion at room temperature. Molecular-scale STM imaging revealed that the TTA SAMs were composed of two mixed phases; an ordered phase with small domains describing a ( 2)R30 structure and a disordered phase. Interestingly, after annealing the pre-covered TTA SAMs on Au(111) at 90 C for 1 h, the small ordered domains grew unidirectionally, resulting in the formation of unique rod-like domains, which were assigned a ( 2)R7 structure. These results will be very useful in understanding the formation and thermal behavior of TTA SAMs on gold surfaces.
Youngdo Joo(주영도),Changbum Kim(김창범),Ilmoon Hwang(황일문),Chongdo Park(박종도) 한국진공학회(ASCT) 2011 Applied Science and Convergence Technology Vol.20 No.1
포항광가속기의 섹터 진공용기에 부착된 빔위치측정기의 수직방향 위치 읽음 값이 갑자기 변하는 오류가 관찰되었다. 이 오류의 원인을 알기 위해서 섹터 진공용기의 양 끝단에 있는 빔위치측정기의 전극을 통한 고주파전달 산란계수를 측정하였다. 급한 변화를 보이는 섹터 진공용기에서는 측정한 산란계수의 첨단 값이 빔위치측정기의 작동 주파수 내에 존재함을 확인하였고, 전산시늉을 통해 빔위치측정기의 작동 주파수내 첨단 주파수가 가로 전장 모드의 공진모드와 일치함을 확인하였다. A sudden step change is observed in the vertical position readings from beam position monitors (BPMs) mounted at the several sector vacuum chambers of Pohang Light Source. To study the source of this sudden step change, we measured the RF transmission scattering matrix (S₂₁) through the pickup electrodes of BPMs mounted at the both ends of the sector vacuum chamber. The measured S₂₁ graph of the sector vacuum chambers suffering sudden step change has a peak in the BPM operation frequency bandwidth. Otherwise that of the other sector vacuum chambers doesn’t have a peak. It is shown by the numerical simulation that the peak found in the BPM operation frequency bandwidth corresponds to the longitudinal harmonic of transverse electric resonance mode.