김동언 교수

For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we carried out an optimization study of various parameters, such as the laser beam transverse profile, the laser pulse length, the laser phase, and the gun energy. The transverse emittance measured at the Injector Test Facility (ITF) is ${\it\varepsilon}_{x}=0.48\pm 0.01~\text{mm}~\text

Pohang Accelerator Laboratory (PAL) have developed a 0.1 nm SASE based FEL based on 10 GeV S-band linear accelerator named PAL-XFEL. At the first stage, PAL-XFEL needs two undulator lines for photon source. The hard X-ray undulator line requires 20 units of 5 m long hybrid-type conventional planar undulator and soft X-ray line requires 7 units of 5 m long hybrid type planar undulators. PAL have developed undulator magnetic structure based on EU-XFEL concepts. In this report, the impact of the ba

Insertion devices (IDs) for the Pohang Light Source (PLS) have been developed and installed into the storage ring to produce higher photon energies. The IDs were fabricated using many Nd-Fe-B permanent magnetic blocks as the source of the magnetic field. The magnetic field characteristics of the IDs heavily depend on the directional uniformity of the magnetization of block sets. This paper describes the Helmholtz coil system (HCS) for measuring the magnetic moments of the blocks, the sorting pro

A reversed current flow in a Z-pinch plasma, which has been observed in previous experiments, is reproduced in a one-dimensional magnetohydrodynamics simulation. The detailed investigation reveals that the formation of the reversed current flow is caused by the propagation of a shock wave. According to the results of the numerical simulation, a new theoretical model, a shock model, is proposed to account for such a phenomenon. The new model shows that a reversed current flow appears when a shock

An ultra-intense short laser pulse incident on a plasma generates a blowout-regime wakefield,where almost all of the electrons are expelled radially by the ponderomotive force. Electrons injected in an off-axis position of the blowout-regime wakefield experience transverse oscillations as well as longitudinal acceleration, and emit intense X-rays from betatron oscillations. In order to investigate the conditions for X-ray generation, we simulated the relativistic electron motion from wakefield p

Laser carbonization of a polymer layer can be employed in various applications in the microelectronics industry, e.g., repairing brightness pixels of an LCD panel. In this work, the process of thermal degradation of LCD color filter polymer by various laser sources with pulsewidths from CW to fs is studied. LCD pixels are irradiated by the lasers and the threshold irradiance of LCD color filter polymer carbonization is experimentally measured. In the numerical analysis, the transient temperature

The only 3rd generation synchrotron light source in Korea, which is operated by the Pohang Accelerator Laboratory (PAL), is planning a major upgrade of the PLS to meet the more demanding requirements of the synchrotron light users. The main features of the major upgrade are (1)increasing the electron beam energy from 2.5 GeV to 3.0 GeV for higher energy X-ray photons, (2)decreasing the electron beam emittance from 18.9 nm to 5.8 nm to increase the photon brilliance,and (3) increasing the number

The past two decades have witnessed the remarkable advance in the new metrology for ultrafast electron dynamics, which allows one to control material processes at electron level and study dynamics far away from equilibrium. This excitement is presented with a brief history of the development and exemplary experiments performed with the new metrology. Applications reviewed include atomic and molecular, condensed-phase science, and advances in X-ray Free electron lasers (XFELs), with an emphasis o