http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
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.
소셜 빅데이터 기반 스마트러닝의 대중 인식 분석 및 요구사항 도출
윤무현(Moo Hyeon Yoon),주다영(Da Young Ju) 한국HCI학회 2024 한국HCI학회 학술대회 Vol.2024 No.1
코로나 19(COVID-19)라는 세계 감염병 대유행을 시작으로 교육계에도 비접촉 온라인 중심의 스마트러닝 교육이 확대되었다. 엔데믹 이후에도 스마트러닝을 통한 교육은 꾸준히 활용되고 있어 본 연구는 대중의 인식을 파악하기 위해 다음과 같이 소셜 미디어 빅데이터 분석을 진행하였다. 첫 번째 ‘스마트러닝’과 ‘AI 교육’ 키워드의 상호관계를 알아보고 두 번째 빅데이터 분석의 결과를 바탕으로 대중의 긍·부정 인식에 영향을 미치는 요구사항을 도출하였다. 분석 결과 스마트러닝의 대중 인식에서 도출된 요구사항을 유형화 하였으며, AI 스마트러닝 개발 방향성 대응이 가능한 설계 요소를 제언한 것에 의의가 있다.
Simulations on the Fast-beam Ion Instability at the PLS
진현창,윤무현,신승환,I. Hwang,K. Ohmi 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.22
The fast-beam ion instability is a significant issue in an electron storage ring. In this paper, a weak-strong simulation code is used to simulate the fast-beam ion instability at the in-vacuum undulators of the Pohang Light Source (PLS) and the PLS-II. The growth time of the vertical oscillation amplitude is calculated for various vacuum pressures. Above the threshold vacuum pressure, the vertical oscillation amplitude exceeds the vertical beam size. The effect of a feedback system is investigated and shows that bunch-by-bunch feedback of 50 turns is effective in suppressing the growth of the vertical oscillation amplitude.
Beam-Optics Analysis and Periodicity Restoration in the Storage Ring of the Pohang Light Source
신승환,윤무현,김은산 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
In this paper, we examine numerically and experimentally linear beam-optics distortion in the storage ring of the Pohang Light Source (PLS) and the correction of optics by using a number of quadrupole magnets installed in the storage ring. The measured orbit-response matrices were .tted to the model-response matrices to obtain . and the dispersion functions in the storage ring. By readjusting the currents of quadrupole-magnet power supplies, we were able to successfully restore the optics parameters to values very close to the design ones. The results revealed that the power- supply current of a quadrupole magnet was o signi.cantly by a maximum of 18 %. After optics correction, the performance of the storage ring is expected to be better.
Measurement and Analysis of a 13 MeV Cyclotron Magnetic Field
신승환,윤무현,김은산,채종서,K. H. Park 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
A four-sector 13-MeV cyclotron magnet, which does not employ the usual trim coils, was designed for positron-emission-tomography (PET) diagnostics. Instead, isochronism was achieved by placing a few side shims, as well as by slightly varying the vertical gap, along the radius of the cyclotron. The magnet was built based on the design, and its magnetic eld was measured using a Hall probe. Equilibrium orbits were computed using the measured data. Then, a series of systematic optimizations of the magnetic eld structure was performed. The nal shape of the magnetic eld was shown to satisfy the simultaneous requirements for isochronism and vertical focusing of the beam. Based on measured magnetic eld, we designed a central region. The cyclotron has been routinely operationed at the Korea Cancer Center Hospital with a nominal beam current of around 50 ㎂.
Electron Cloud Instability at Cser-TA
진현창,윤무현,K. Ohmi 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.61
The electron cloud instability (ECI) is a signi¯cant issue at the International Linear Collider Damping Ring (ILC-DR) which can limit the performance. A new lattice called Cesr-TA has been developed from the Cornell Electron Storage Ring (CESR) for ILC-DR research. We investigate beam instabilities caused by the electron cloud in the Cesr-TA lattice. We simulate the interaction of a bunch and a cloud by using the uniform beta function lattice and the real lattice models of Cesr-TA. The simulation results are favorably compared with the analytic estimates.
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.
Sandeep Kumar,윤무현 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6
For a tightly focused laser, the beam-waist radius is of the same order as the wavelength and the lower-order-corrected Gaussian pulse description satisfies Maxwell's equations less accurately, so it becomes necessary to include all the field components that arise from the tight focusing of the laser so as to satisfy Maxwell's equations more accurately. The effect of the seventh-order-corrected chirped Gaussian laser beam on the electron acceleration in vacuum is investigated. A numerical simulation shows that an electron maximum energy gain on the order of giga-electron volts (GeV) can be expected in the beam-waist region 45≤k0w0≤60, where k0 is the laser wave number and w0 is the laser-beam's waist size at the focal point of the beam.