K. H. Park

Improvement of the pulsed wire method for undulator magnetic-field measurement

The U10 undulator for the Pohang Light Source was measured with a pulsed wire measurement (PWM) method. By adjusting the aperture of the slotted optical switch (SOS) for PWM, the sensitivity of SOS output to the wire displacement improved significantly. A calibration table, which translates the output voltage to the displacement of wire, was obtained and the linearity of the PWM was enhanced using this table. The magnetic-field profile of the U10 undulator measured with the PWM method agrees well with that measured with Hall probe mapping. The effect of the wire dispersion on PWM is also discussed.

Designing a Multi-user Interactive Simulation Using AR Glasses

In this research, we present the design and formative evaluation of an interactive simulation for informal learning environments. The wearable feature of Augmented Reality(AR) glasses enables full-body movement and embodied interactions in digitally augmented physical environments. The interactive simulation was developed to engage and immerse users to understand an abstract scientific concept about the refraction of light. To design playful and meaningful learning experiences, several design features related to social interaction, multi-user interaction, and embodied interaction were unpacked and integrated in the design process. Through the formative evaluation with participants in the laboratory setting, we found several possibilities and challenges about designing an interactive simulation in informal learning contexts using AR glasses.

Field Mapping System for Solenoid Magnet

A three‐dimensional Hall probe mapping system for measuring the solenoid magnet of PLS photo‐cathode RF e‐gun has been developed. It can map the solenoid field either in Cartesian or in cylindrical coordinate system with a measurement reproducibility better than 5 × 10−5 T. The system has three axis motors: one for the azimuthal direction and the other two for the x and z direction. This architecture makes the measuring system simple in fabrication. The magnetic center was calculated using the measured axial component of magnetic field Bz in Cartesian coordinate system because the accuracy of magnetic axis measurement could be improved significantly by using Bz, instead of the radial component of magnetic field Br. This paper describes the measurement system and summarizes the measurement results for the solenoid magnetic of PLS photo‐cathode RF e‐gun.

A new PLS-II in-vacuum undulator and characterization of undulator radiation

This paper describes the result of overall studies from development to characterization of undulator radiation. After three years of upgrading, PLS-II has been operating successfully since 21st March 2012. During the upgrade, we developed and installed an in-vacuum undulator (IVU) that generates brilliant X-ray beam. The IVU with a 3 GeV electron beam generates undulator radiation up to ~ 21 keV by using 11th higher harmonic. The characterizations of the undulator radiation at an X-ray beam line in PLS-II agreed well with the simulation. Based on this performance demonstration, the in-vacuum undulator is successfully operating at PLS-II.

Towards Designing a Mobile Social Learning Application with Meaningful Gamification Strategies

In this paper, we present the research in-progress, which aims to design a mobile application that can support social learning experiences in a game-like environment. Our research was mainly motivated by the fundamental dilemma in children and new media that the penetration of digital media in childrens life poses both opportunities and risks. Adopting the key ideas of serious games, we have been investigating the design and development of a mobile social learning application leveraging the affordances of social networks and gamification. The purpose of this paper is to provide the initial design framework that has guided the design of our mobile social learning application. In particular, we present the analysis of the existing social networking sites designed for children, and extracted essential features. Overall, we found that the existing platforms are lack of supporting childrens internal motivation, and adaptation features for emergent and customizable structures. Design ideas and rationales are presented to demonstrate how our application has been conceptualized to incorporate meaningful gamification and adaptive learning strategies.

Conceptual design of a 14 cm period multipole wiggler at PLS

Pohang Accelerator Laboratory (PAL) is developing a Multipole Wiggler (MPW14) to utilize high-energy (B30 keV) synchrotron radiation at Pohang Light Source (PLS). The MPW14 is a hybrid type device to achieve maximum peak flux density and wide beam fan that can serve two beamlines. PLS MPW14-features period of 14 cm, minimum gap of 14 mm, 20 full field periods, maximum flux density of 2.06 T, 3036 mm total magnetic structure length. The peak flux density is very high compared to the other wigglers of similar pole gap and the period. The high peak flux density was possible using advanced new magnetic material and optimized magnetic geometry. The MPW14 will be used in hard X-ray region of 10–30 keV at 2.5 GeV electron energy. The total photon power is 6.19kW and the peak power density is 5.27 kW/mrad 2 at 2.5 GeV, 150 mA. To withstand the big magnetic loads with minimum deflections, C-type support structure is designed with detailed FEM structural analysis. In this article, all the conceptual design efforts for the PLS MPW14 wiggler will be described. r 2001 Elsevier Science B.V. All rights reserved. PACS: 41.85.L

Dynamic feedback mechanism for maximizing interaction in online social network services

Online social network services have embedded social rating systems that users can evaluate and share the quality of content such as the “Like” button for Facebook. This rating system is an important mechanism in social interaction since the system can affect the degree of user connection and the spread of information sharing. Most of such social rating systems, however, are based on the fixed feedback mechanism, where users cannot communicate their emotion and evaluation toward certain content in a real-time manner. In this research, we propose a novel feedback method that dynamically updates rating scores in social network services to give users immediate feedback. To confirm the usefulness of dynamic feedback mechanism compared to the current static feedback mechanism, we conducted an exploratory experiment with 46 participants in a simulated Facebook situation. Since types of content matter for the nature and degree of social interaction, we assumed that the dynamic feedback mechanism might yield different effects to different types of content. Hence, in the experiment, we included three different types of content, namely a) user-generated content, b) news article, and c) commercial advertisement, to examine the interaction effect between feedback mechanism and content types. The dependent variable was the number of “Like” clicks. The results indicate that the dynamic feedback type received significantly higher “Like” clicks than the fixed feedback type. Further, there was a significant interaction effect between feedback types and content types. The dynamic feedback mechanism was the most effective for the user-generated content type.

Physics Requirements of PAL‐XFEL Undulator

Pohang Accelerator Laboratory(PAL) is planning a 0.3 nm SASE (Self Amplification of Spontaneous Emission) XFEL based on 3.7 GeV linear accelerator. For short saturation length, application of SPring8 type in vacuum undulator is needed. This reflects the experiences from SPring8 SCSS project. The end structures were designed to be asymmetric along the beam direction to ensure systematic zero 1st field integral. The thickness of the last magnets were adjusted to minimize the transition distance to the fully developed periodic field. This approach is more convenient to control than adjusting the strength of the end magnets. The final design features 4 mm minimum pole gap, 15 mm period, peak effective field of 1.09 Tesla. In this article, the physical design of the undulator, the design of the end structure, and the physics requirements of the undulator system will be presented.

Design of High Field Multipole Wiggler at PLS

Pohang Accelerator Laboratory (PAL) is developing a high field multipole wiggler for new EXAFS beamline. The beamline is planning to utilize very high photon energy (∼40keV) synchrotron radiation at Pohang Light Source (PLS). To achieve higher critical photon energy, the wiggler field need to be maximized. A magnetic structure with wedged pole and blocks with additional side blocks which are similar to asymmetric wiggler of ESRF are designed to achieve higher flux density. The end structures were designed to be asymmetric along the beam direction to ensure systematic zero 1st field integral. The thickness of the last magnets were adjusted to minimize the transition sequence to the fully developed periodic field. This approach is more convenient to control than adjusting the strength of the end magnets. The final design features 140mm period, 2.5 Tesla peak flux density at 12mm pole gap, 1205mm magnetic structure length with 16 full field poles. In this article, all the design, engineering efforts for the ...

AC Power Supply for Wobbler Magnet of the MC-50 Cyclotron

A wobbler magnet and an AC power supply for the MC-50 cyclotron (k=50) at Korea Institute of Radiological and Medical Sciences (KIRAMS) were designed and constructed to increase the area of beam irradiation. The power supply has two independently operating channels for the vertical and horizontal coils of the wobbler magnet. The frequency of the AC power supply for both coils is programmable from 1 to 20 Hz in a step of 1 Hz, and the maximum output current is 12 A rms. With the wobbler magnet, the uniform irradiation area of the proton beam increased ∼ 4 times larger than the one without the magnet, and various properties of the magnet and power supply system indicate that the system is well suited for many ion beam experiments.