1,721,441 research outputs found
Current Activities in the Korean Accelerator Community
No full textSince 1988 when Pohang Light Source (PLS) started its construction, the Korean accelerator community has grown very fast and has expanded from electrons to protons and to rare isotopes. At this moment, there are four major activities: the Proton Engineering Frontier Project (PEFP) in Gyeongju, the Korea Rare Isotope Accelerator (KoRIA), the PLS-II, which is an upgrade of the current PLS, and the X-ray Free Electron Laser (XFEL). Besides these major activities, there are several industrial accelerators and medical ones. In this report, the details of these activities are summarized.11sciescopuskc
Accurate Method for Estimating of the Charge in the Bunching Part of an Electron Beam by Using an Electro-Optic Crystal
No full textElectro-optic sampling (EOS) is a promising method to measure various properties of an electron beam non-destructively. An analysis procedure for electro-optic (EO) measurements to estimate the charge in the bunching part of an electron beam whose shape is not Gaussian is introduced in this paper. Experimental results measured by using the EO method are analyzed in terms of the relative phase shift between the horizontal and the vertical components of the laser. A simulation study is done with the pulse propagation method, which utilizes the Fourier transform to investigate the evolution of an electromagnetic pulse inside the EO crystal. The analysis result of the EO measurement expressed in terms of the relative phase shift is compared with the simulation and it shows a good agreement with the beam charge. The charge in the bunching part of the electron beam can be estimated accurately by using the analysis procedure in this paper.11sciescopuskc
Spatio-temporal measurement of beam properties in the PLS diagnostic beamline
No full textA diagnostic beamline is being constructed in the PLS storage ring for measurement of electron-and photon-beam properties. It consists of two 1:1 imaging systems: a visible-light imaging system and a soft X-ray imaging system. In the visible-light imaging system, the transverse beam size and beam position are measured with various detectors: a CCD camera, two photodiode arrays and a photon-beam position monitor. Longitudinal bunch structure is also investigated with a fast photodiode detector and a picosecond streak camera. On the other hand, the soft X-ray imaging system is under construction to measure beam sizes with negligible diffraction-limited error. The X-ray image optics consist of a hat cooled mirror and two spherical focusing mirrors.11sciescopu
A Study of the Energy Spread Effect for an Electron Diffraction Experiment
No full textA 2.5 MeV electron beam for femtosecond electron diffraction is generated from a RF photocathode gun with the Brookhaven National Laboratory (BNL) gun IV type at the Pohang Accelerator Laboratory. We use a Ti:Sapphire laser system to illuminate the Cu photocathode with a 100 fs laser pulse. The energy spread of the electron beam is measured to be lower than 0.2% with a 23 degrees RF phase for oblique laser injection. Beam charge is estimated to be its low as 1 pC. The chromatic coherence length is estimated to be 0.106 angstrom. The diffraction patterns for polycrystalline aluminium are studied numerically with several electron beam energies with finite, energy spread. The blurred pattern is quantified to investigate the effect; of the energy spread on the diffraction pattern. A higher energy electron beam blurs the diffraction image more than a lower energy one.11sciescopuskc
Analysis of the electro-optic measurement of an electron beam with new refractive indices
No full textElectro-optic sampling (EOS) is a promising method of measuring the electron bunch length and arrival time nondestructively. When an electric field is applied to the EO crystal, the EO crystal shows birefringence which is described by an ellipsoid of refractive indices. The ellipsoid can be expressed with the principal axes associated with the crystallographic axes. If a linearly polarized laser is passing through the EO crystal with external electric field, the polarization of the laser is modulated elliptically or even circularly. The polarization modulation of the laser probe beam should be expressed in terms of the relative phase shift between the decomposed vectors of the laser. Conventional analysis assumes that the polarization direction of the laser probe beam is to set to be at an angle of 45 degrees with the principal axes. Only the principal refractive indices have been used until now with this assumption. However, if the position of the electron beam is changed in experiments, the electric field applied to the EO crystal is also changed. Thus, the directions of the principal axes of the isotropic crystal are also changed. The principal axes do not make an angle of 45 degrees anymore with the fixed polarization vector of the laser probe beam in this situation. New refractive indices are needed to explain the experimental result with such deviation properly. In our work, new refractive indices are derived and simulation studies are carried out with the pulse propagation method, which utilizes the Fourier transform to investigate the evolution of the electromagnetic pulse inside the EO crystal. Experimental results are in good agreement with the prediction from the simulation with newly derived refractive indices.11sciescopu
Optimal Charge of a Photocathode Gun for a Compact X-ray Free-Electron Laser
No full textFor a photocathode gun, the optimal charge per gun pulse is derived to give the theoretically allowed smallest saturation length of the X-ray free-electron laser based on the self amplified spontaneous emission scheme. The derivation is approximate, but the result is practically independent of specific machine design. The objective is to contribute to the study of a compact X-ray free-electron laser. (C) 2010 The Japan Society of Applied Physics11sciescopu
Test bed of control system using multimedia technology at PLS
No full textWe have developed the test bed of control system for the Pohang Light Source (PLS) by using multimedia technologies. This test bed consists of three parts: a man-machine interface (MMI) with media data management, a data acquisition system, and a networking system. The MMI that contains specific application software is developed with an application program interface and a multimedia user interface toolkit. We use 100 Mbps Ethernet as a network system and a commercial database named ObjectStore to store data. Several VME systems with OS-9 operating system and PLC systems are used in the data acquisition layer. We present the result of test bed development.11sciescopu
Reduction of the higher-order field distribution in a photocathode rf gun for the X-ray free electron laser
No full textThe mechanism of the higher-order rf field elimination in the photocathode rf gun used for the X-ray free electron laser (XFEL) machine is discovered. The analysis and the measurement results of the rf field in several models of the rf gun with several holes at the cavity wall are presented. The contribution of the holes to the asymmetrical distribution of the rf field along the azimuthal angle is measured with several model cavities. Using a comparison between the experimental results and the numerically-obtained rf field distribution, we can reveal that the origin of the quadrupole component growing at the cavity with two holes and of the octapole component growing at the cavity with four holes is the superposition of the rf fields in the cavity. Two kinds of model cavities with several holes at the cavity wall have been fabricated, and the rf field distributions of the model cavities have been measured to compare with the theoretical analysis and the numerically-obtained rf field. From the analyses, we decided to adopt an rf gun that has dual feeds and two pumping holes for the Pohang Accelerator Laboratory (PAL-XFEL) project.11sciescopuskc
Generation of high-energy electrons by a femtosecond terawatt laser propagating through a sharp downward density transition
No full textWe demonstrate by computer simulations the generation of high-energy electrons by using a femtosecond terawatt laser pulse propagating in a plasma with a sharp downward density transition. In the two-dimensional simulation, a 20-TW laser pulse with a pulse duration of 60 fs and a wavelength of 800 nm propagates through a plasma with a sharp density transition consisting of n(0)(I) = 5 x 10(18) cm(-3) and n(0)(II) = 0. 75n(0)(I). The simulation result demonstrates that a significant amount of electrons can be self-trapped and accelerated to an energy of 117 MeV over a distance of 0.62 mm by the ultrastrong nonlinear laser wake field. In addition, it has been found that the trapping dynamics is much different from the electron-beam-driven dynamics and that the energy spread of the trapped electrons can be reduced significantly by use of the density tapering method. (C) 2004 Optical Society of America.11sciescopu
The beam based alignment technique for the measurements of beam position monitors offsets and beam offsets from quadrupoles in the Pohang Light Source
No full textThe beam based alignment (BBA) technique is applied to the 2-GeV storage ring of the Pohang Light Source to measure the offsets of beam position monitors. This measurement is particularly necessary for brain position monitors (BPMs) plugged into a long (similar to 10m) aluminum chamber, since the mechanical deformation of the vacuum chamber is experienced after repeated heating for the outgassing process, and the BPM positions are changed accordingly. A part of the excitation current of each quadrupole magnet is shunted through an electronic shunt circuit. Then, the closed orbit receives a perturbation due to the current reduction. Using two quadrupole magnets, we can measure the offset of each BPM. Also, the BBA technique is applied to measure the beam offsets from the center of quadrupole magnets, and gives information to the survey team about which quadrupole magnets should be aligned mostly. in this process, we introduce the merit function to reduce various errors such as BPM characteristic changes and the lattice imperfection. By minimizing the merit function, we can get the beam offset as the maximized expectation value. This paper presents the BBA technique used and experimental results taken from the 2-GeV Pohang Light Source (PLS) storage ring. When the BPM offset is measured, it is observed that a 3% of the shunt current is suitable.11sciescopu
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