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Impedance Analysis with Longitudinal Bunch-Shape Measurements
황일문,김은산,윤무현 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.3
We used a streak camera to measure the longitudinal bunch shape of a circulating electron beam in the 2.5-GeV Pohang Light Source (PLS). The measured results were analyzed by an (R+L) series model to obtain a resistance R = 1.1 k, an inductance L = 89 nH, and a longitudinal impedance jZ=njeff= 0.6 . The scaling law for the bunch lengthening is expressed as ¾l / I0:22§0:01. The eect of insertion device in the ring on the impedance, particularly the eect of the vertical height of the in-vacuum undulator currently placed in the PLS ring, is presented.
FEL Simulation of the 0.1-nm Hard X-ray from the PAL-XFEL
황일문,한장희,박용운,이재유 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.2
The Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) will provide X-rayFEL radiation in the range of 0.1 and 10 nm with five undulator beamlines. An undulator beamlinefor hard X-ray is designed for 0.1-nm self-amplified spontaneous emission FEL. When a 200-pCelectron bunch with a 10-GeV energy and a 0.5-μm·rad normalized emittance passes the undulators,1012 photons at 0.1 nm will be generated within 100 fs. The wakefield effect of the vacuum chambermay reduce the radiation power significantly, but a proper tapering in the undulator can recoverthe power. We present a study in which GENESIS 1.3 was used for the FEL simulation.
Improvement of the Micro-pulse Structure for Top-up Operation at the Pohang Light Source
황일문,김창범,손윤규,전명환 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.22
The beam current of the storage ring slowly decreases with time and is filled by periodic injection. The top-up operation uses a short time-interval injection to keep the current roughly constant. The injection efficiency in the top-up operation should be high in order to reduce the radiation caused by beam loss. In the previous design, the beam loss could not be eliminated because the electron pulse generated by the electron gun was longer than the RF bucket. To suppress the loss, we reduced the length of the gun pulse to 0.25-ns full width at half maximum, which is a fourth of the previous length. Additionally, the RF phases of the ring and the linac were synchronized to optimize the micro-pulse structure. The micro-pulse structure with synchrotron motion and RF synchronism was measured at the Pohang Light Source (PLS) by using a streak camera. A tracking simulation of the pre-injector is also presented.
Two-dimensional SR Interferometer for PLS-II
김창범,황일문,최효진,박성주,Jung-Yun Huang,박용운,고인수,류진영,황지광 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.4
A synchrotron radiation (SR) interferometer was used for beam size measurements at the Pohang Light Source (PLS). It was an one-dimensional (1D) interferometer, and the horizontal beam size was only available for real time measurements of the user service. In the PLS upgrade project (PLS-II), a 2D interferometer was tried for simultaneous measurements of the horizontal and the vertical beam sizes. Various sizes of the 2D slits were tried to find an optimum condition by considering the SR characteristics and the instrument’s limitations. Measurement results of the beam size were cross-checked in three different ways and showed good agreements with each other. After optimization, the measurement accuracy of the beam size was improved significantly, and a vertical beam size change was noticed when the gap distance of the elliptically polarized undulator (EPU) was changed.
Energy Feedback System for the PLS-II Linac
김창범,김문경,황일문,최재영,신승환,김성철,박종두 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.11
The upgraded Pohang-Light-Source (PLS-II) was opened to the public in 2012. Among many improvements of the PLS-II, a top-up operation was one of the highlights of them, and the stability of the electron beam was improved significantly. For the top-up operation, a stable injection from the linac to the storage ring was critically important, so that an energy feedback system was introduced to reduce the energy jitter of the linac electron beam. The result of the feedback system was successful and the measured energy jitter was less than ±0.1% (rms). In this work, the details of the energy feedback system are presented. It includes the setup for the energy feedback system, measurement results in the optimization process, and the future work for a better performance.
The 0.1-nm SASE FEL at the Pohang Accelerator Laboratory
윤무현,김동은,황일문,김은산 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.5
A next-generation synchrotron-radiation source planned at the Pohang Accelerator Laboratory (PAL) is described in this paper. It is a linac-based free electron laser (FEL) to produce an intense X-ray pulse down to a 0.1-nm wavelength with a 100-fs rms pulse length. This will make it possible for pump-probe experiments, such as dynamics studies of chemical reactions and coherent diffractive imaging, with a peak brilliance approximately ten orders of magnitude higher than that from the third-generation light source. The in-vacuum undulator with a 5.3-mm gap is employed in conjunction with an S-band rf linear accelerator to produce a 10.053-GeV electron beam. If an 1-nC electron beam with a 1.1-mm mrad normalized emittance and a 0.015 % relative energy spread passes through the undulator, an output radiation power of GW is expected in approximately a 94-m saturation length. The effect of the wakefields on the lasing performance is also considered and is shown to be acceptable with the chosen undulator gap.
주영도,김창범,황일문,박종도,Joo, Young-Do,Kim, Chang-Bum,Hwang, Il-Moon,Park, Chong-Do The Korean Vacuum Society 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 $S_{21}$ 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.
Correlation Study of a Beam-position Monitor and a Photon-beam-position Monitor in the PLS-II
김창범,신승환,황일문,이병준,주영도,하태균,윤종철,김경화,김문영,이은희,김일유,황정연 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.2
The beam stability is one of the most important issues for the user service of the synchrotronradiation facility. After the upgrade of the Pohang Light Source (PLS-II), the electron-beam orbitis maintained within a root-mean-squred (rms) 1-μm range by using an orbit feedback system. However, that does not guarantee the radiation stability at the end of the beamline because unknownfactors, such as focusing mirrors and double-crystal monocrometers, are present in the beamline. As a first step to solve this problem, photon-beam-position monitors (PBPMs) are installed in thefront ends of the beamline to monitor the radiation stability. If the radiation is stable at the startingpoint of the beamline, we can move to the other components downstream that make the radiationunstable. In this paper, a correlation study will be presented between the beam-position monitor(BPM) and the PBPM. In addition, the effect of the orbit feedback system on the correlation willbe described.