Chinwha Chung

Systematics of Differential Photoneutron Yields Produced from Al, Ti, Cu, Sn, W, and Pb Targets by Irradiation of 2.04 GeV Electrons

Differential photoneutron yields produced from Al, Ti, Cu, Sn, W, and Pb targets by an irradiation of 2.04 GeV electrons were measured at the angle of 90° relative to the incident beam. The neutron energy range measured in this experiments was between 10 and 400 MeV. The systematics of the yields was studied for two target conditions : a target element and a target thickness. The neutron productions by a photonuclear reaction and by a hadron cascade due to secondary particles were considered to develop semi-empirical formula for the application of shielding calculation.

Introduction of the high radiation resistance of undulator magnet

One of the neodymium‐iron‐boron (Nd2Fe14B) magnet with high coercivity was found to show very high resistance to irradiation. The sample was irradiated with 2.0 GeV electrons. The radiation‐induced demagnetization of this Nd2Fe14B magnet was as small as that of the samarium‐cobalt (Sm2Co17) magnets, known as to show high radiation resistance, irradiated under same experimental conditions for comparison.

Photoneutron Spectra from Thin Targets Bombarded with 2.0 GeV Electrons

Photoneutron spectra produced from thin targets bombarded with 2.04 GeV electrons were measured in the range from 9 MeV to 300 MeV by using the time of flight technique. The measurements were carried out for thin C, Al, Cu, Sn, and Pb targets at a fixed angle of 900 to the beam direction. In this data reduction a removal cross-section was newly calculated for compensating the effect of the Pb attenuator which was set to suppress γ-flash signal. The double differential yields per incident electron were obtained from the spectra as a function of the mass number of target elements. For neutron energies larger than 20 MeV the yields decreased with higher mass number of the target, which was consistent with other authors’ published results.

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.

Improvement of radiation resistance of NdFeB magnets by thermal treatment

The effect of the thermal stabilization on the radiation sensitivity of neodymium‐iron‐boron (Nd2Fe14B) undulator magnets to high‐energy electron irradiation was investigated. The sample magnets were baked in an oven for 24 hours before irradiation, and the temperatures of this thermal treatment were varied from 142 °C to 240 °C. All of the thermally stabilized magnets showed higher resistance to irradiation with 2.0 GeV electrons than unbaked sample. Their demagnetization curves decreased linearly with respect to the number of electrons, and with a demagnetization rate remarkably smaller than that of the unbaked magnets. Though, when the stabilizing temperature exceeded some point, the resistance showed small decrease.

Combination PBPM and Slits at the Pohang Light Source

Three combination photon beam position monitor (PBPM) and slits are in use at the photon transfer line (PTL) of the high flux macromolecular X‐ray crystallography (HFMX) beamline at the Pohang Light Source. Each slit, based on a common basic design, drives its two slit plates through a double bellows assembly by two motors. The slits also adopt a turned‐grazing inclination of 30° to restrict the passage of scattered photon beams and to enhance cooling efficiency. One of the slits has been successfully applied with cooling function in order to cool the heat load from a multi‐pole wiggler. This paper describes the design details and design features of the slits and discusses the results of performance tests for their PBPM function. The combined PBPM function can be used for the analysis of the position behaviors of photon beams at the beamline.

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 ...

Operational Experience of Cooling Water Systems for Accelerator Components at PLS

The PLS cooling water system has been utilized for absorbing thermal load generated by a multitude of electromagnetic rf power delivering networks at PLS. The low conductivity cooling water for heat removal from the accelerator components is deionised and filtered to more than 2 MΩ·cm of specific resistance. The operation temperature of dedicated components in the accelerator is sustained as tight as ±0.1°C to minimize the influence of temperature fluctuation on the beam energy and stability. Although the PLS cooling systems were initially installed with a high degree of flexibility to allow for the conditioned operations for high beam gain, the system improvements and repairs have been employed to enhance the operational performance and reliability, and to incorporate the newly developed operating interfaces such as EPICS accelerator control systems.

Preliminary Design Efforts of the X-ray SASE at PAL

Pohang Accelerator Laboratory(PAL) is working on a X‐ray self‐amplified spontaneous emission (SASE) FEL which will be driven by the upgraded injector linac. The preliminary idea is to upgrade the existing 2.5GeV injector linac to 3.0 GeV electron energy and use it as a driver for X‐ray SASE FEL. It also features utilization of the recent in vacuum undulator technology for shorter radiation wavelength . And the 3rd harmonic enhancement is considered for a possible option. In this report, the preliminary conceptual designs of the X‐ray SASE FEL at PAL including above features will be described.