In Soo Ko

Measurement of photoneutron spectrum at Pohang Neutron Facility

The Pohang Neutron Facility, an electron linear accelerator (linac) based pulsed neutron facility, was constructed for nuclear data production in Korea. It consists of an electron linac, a water-cooled Ta target with a water moderator, and a time-of-flight path with an 11 m length. The neutron energy spectra are measured for different water levels inside the moderator and compared with calculations by the Monte Carlo N-Particle transport code. The optimum size of the water moderator is determined based on these results.

Design study on standing-wave linear accelerator

A compact standing-wave linac has been designed using S-band microwaves for medical and industrial applications. It uses a bi-periodic structure with constant impedance. It consists of a buncher section with three-cells and on-axis coupled cavities with nine-cells. The total length is 740.0 mm including the electron gun. Using SUPERFISH, HFSS and PARMELA codes, it is capable to deliver 4.5 MeV electron beams with pulsed microwaves of 4.8 MW at 2,856 MHz. In this paper, we present the detailed design studies on a compact S-band standing-wave linac.

Upgrade of Pohang Light Source (PLS-II) and Challenge to PAL XFEL

In December 10, 2010, the Pohang Light Source (PLS) permanently stopped its operation. The PLS was the first third-generation light source in Korea and operated for 15 years. The PLS energy was 2.5 GeV. With strong user requests to increase the number of high-quality insertion device (ID) beamlines and to further improve beam quality of the PLS, the Pohang Accelerator Laboratory (PAL) started a new project in 2009 to convert the old PLS to a new and advanced third-generation light source, PLS-II [1]. The PLS-II project period and budget were three years from 2009 and US

Measurement of neutron total cross-section of Dy at Pohang Neutron Facility

100 M. The project was successfully completed on time and within budget in 2011. The PLS-II fully opened its door to users on March 21, 2012.

Measurement of neutron total cross-sections of Dy and Hf in the energy region from 0.002 to 100 keV

Abstract The neutron total cross-section of natural Dy has been measured in the energy region from 0.025 eV to 100 eV by the neutron time-of-flight method at Pohang Neutron Facility, which consists of an electron linear accelerator, a water-cooled Ta target with a water moderator, and a time-of-flight path with an 11 m length. A 6Li–ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.5 cm has been used as a neutron detector and a metallic plate of Dy sample have been used for the neutron transmission measurement. The background level has been determined by using notch-filters of Co, Ta, and Cd sheets. In order to reduce the gamma rays from a Bremsstrahlung and that from a neutron capture, we have employed a neutron-gamma separation system based on their different pulse shape. The present measurements are in general agreement with the previous ones and the evaluated data in ENDF/B-VI. The resonance parameters of Dy isotopes (161,162,163Dy) have been extracted from the transmission data by using the SAMMY code and compared with the previous ones.

Progress of PLS 2-GeV linac

Abstract The neutron total cross-sections of Dy and Hf have been measured in the energy region from 0.002 to 100 keV by the neutron time-of-flight method with a 46 MeV electron linear accelerator of the Research Reactor Institute, Kyoto University. A 6Li glass scintillator has been used as a neutron detector and metallic plates of Dy and Hf samples, 0.5–5.0 mm thick, have been used for the neutron transmission measurement. The neutron flight path from the water-cooled Ta target to the 6Li glass scintillator is 22.1±0.01 m. The background level has been determined by the block-off method and/or by using notch-filters of Co (132 eV), Ag (5.2 and 16.3 eV) and Mn (336 eV) and a Cd sheet. The present measurements are in general agreement with the previous ones and the evaluated data in ENDF/B-VI.

A Simulation Study of the Global Orbit Feedback System for Pohang Light Source

Pohang Accelerator Laboratory (PAL) is constructing the 2-GeV Pohang Light Source (PLS). The 2-GeV electron linear accelerator will be used as a full energy injector to the storage ring. There are 42 accelerating columns in the 150-m long linac. The linac is powered by 11 klystrons of 80-MW maximum output power, which are driven by 200-MW modulators. Two 200-MW modulators connected to the klystrons are already under normal operation, and assembly work for the nine remaining modulators is in progress. In the tunnel, about half of the linac has been installed. The cooling system is completed along with the precision temperature controllers. The installation work will be completed by the end of 1993. We present the updated construction progress of the PLS 2-GeV linac.<<ETX>>

Reduction of Multipole Fields in Photocathode RF Gun

This paper describes the simulation of the global orbit feedback system using the singular value decomposition (SVD) method, the error minimization method, and the neural network method. Instead of facing unacceptable correction result raised occasionally in the SVD method, we choose the error minimization method for the global orbit feedback. This method provides minimum orbit errors while avoiding unacceptable corrections, and keeps the orbit within the dynamic aperture of the storage ring. We simulate the Pohang Light Source (PLS) storage ring using the Methodical Accelerator Design (MAD) code that generates the orbit distortions for the error minimization method and the learning data set for neural network method. In order to compare the effectiveness of the neural network method with others, a neural network is trained by the learning algorithm using the learning data set. The global response matrix with a minimum error and the trained neural network are used to the global orbit feedback system. The simulation shows that a selection of beam position monitors (BPMs) is very sensitive in the reduction of rms orbit distortions, and the random choice gives better results than any other cases.

The Beam Based Alignment Technique for the Measurements of Beam Position Monitors Offsets and Beam Offsets from Quadrupoles in the Pohang Light Source

Photocathode rf gun, the high-brightness electron source with extremely low emittance is highly required for future light sources such as X-ray free electron lasers (XFEL). The coupling hole between the waveguide and the cavity of a photocathode rf gun causes asymmetries in the rf fields at the coupler cell. The dipole and quadruple fields are the dominant sources of the transverse rf emittance growth. In the BNL Gun-III, the dipole field is reduced by adding a symmetric pumping hole at the opposite side of the waveguide coupling hole. The dipole field can be reduced further by adjusting the size of the pumping hole. However, the quadruple field cannot be suppressed by the single pumping hole. We have designed new rf cavity in which the quadruple field as well as the dipole one are suppressed. In this design, two additional pumping ports are placed at the 90° positions with respect to the coupling hole and the pumping holes. Beam dynamics simulation for newly designed rf gun shows that the vertical transverse emittance is reduced by about 60% compared to the old one.

Performance characteristics of the pulsed high power klystron tube for PLS 2-GeV Linac

The 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 beam position monitors (BPMs) plugged into a long (~10 m) 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.