I. S. Ko

Synchrotron Radiation Facilities in Korea: Pohang Light Source and Future XFEL Project

The Pohang Light Source (PLS) at the Pohang Accelerator Laboratory (PAL) is a third-generation light source, the only synchrotron radiation facility in Korea, and the fifth machine of its kind in the world (see Figure 1). In 1988, PAL was organized for the construction of the PLS. Ground-breaking was celebrated in 1991, and PLS construction was completed in 1994. In 1995, the PLS opened two beamlines to public users. The PLS was initially operated at 2.0 GeV in 1995. Since 2002, the energy of the electron beam has been upgraded to 2.5 GeV (see Table 1 for the principal parameters of PLS). Remarkable increases in the number of beamlines, users, and scientific results have been achieved since the opening of the PLS in 1995. Two or three beamlines have been added each year for the past 15 years, and as of February 2009 we have in total 27 beamlines in operation and 3 beamlines under construction, which will be completed by the end of 2009 (Figures 2 and 3).

Control system of PLS 2-GeV electron linac

A graphic-based realtime control system is developed and used for commissioning and operation of the PLS 2-GeV electron linac. The system has three layers of hierarchy; operator interface computer, supervisory control computer (SCC) for data processing, and device interface computer (DIC) for distributed data acquisition. The operator interface is based on the UNIX system with a graphic-based development system named RTworks. The SCC consists of three subsystems; modulators, magnet power supplies, and beam diagnostics. DICs attached to individual devices are placed in the 200-m linac building. There are altogether 23 VME CPUs and various I/Os in both SCC and DIC levels. The realtime operating system is OS-9. The major role of DICs is to control and to monitor individual devices upon operator`s requests. The SCC updates variable database from DICs and conveys commands from the operator to DICs. SCCs and DICs are connected through a local area network to form a client/server system. Low-cost workstations are used for the operator interface. In order to have quick manipulation and easy understanding, the authors use intensive graphics for the control windows.

Pulsed neutron source using 100-MeV electron linac at Pohang Accelerator Laboratory

The Pohang Accelerator Laboratory uses a 100-MeV electron linac for the pulsed neutron source as one of the long-term nuclear R&D programs at the Korea Atomic Energy Research Institute. The linac has two operating modes; one for short pulse mode with the various repetitions between 2 ns and 100 ns and the other for long pulse mode with 1 /spl mu/s. The major beam parameters are as follows; the nominal beam energy is 100 MeV, the maximum beam power is 10 kW, and the beam current is varied from 300 mA to 5 A and depends on the pulse repetition. We constructed and tested a test-linac based on the existing equipment such as a SLAC-5045 klystron, two constant gradient accelerating sections, and thermionic RF-gun. We describe the characteristics of the test-linac and report the status of the pulsed neutron source facilities including a target system and time-off-flight paths.

Computer control system of PLS 2-GeV storage ring

A real-time computer control system has been developed and is used for the precise remote operation of the Pohang Light Source (PLS) 2-GeV storage ring. It consists of three layers of computer systems: console computer for operator interface, subsystem control computer (SCC) for front-end data processing, machine interface unit (MIU) for low-level data acquisition. The console computer is a Sun Microsystems SPARC station with UNIX. It uses X-Window/Motif for the GUI (graphic user interface) tool. The SCC acts as a front-end data processing between the console computer and the MIU. There are 24 MIUs placed in the storage ring building. The MIU is directly connected to individual machine components to do low-level data acquisition. The SCC and MIU are based on VMEbus standard and use Microwares OS-9 real-time operating system. Console-computers and SCCs are connected through Ethernet (TCP/IP). SCCs and MIUs are connected through MIL-STD-1553B fieldbus. This paper presents general hardware and software structures of the control system.

Test bed of control system using multimedia technology at PLS

We 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.

High-power test of thermionic RF-gun at the Pohang Accelerator Laboratory

A one-cell RF-gun with a dispenser cathode was fabricated for high-brightness applications at the Pohang Accelerator Laboratory. The gun was designed to withstand heavy beam loading and breakdown for long-pulse operation. After some RF-conditioning, the gun could be powered up to a nominal RF-power of 3.5 MW during 6 /spl mu/s. The gun produced an electron beam with an average current of 300 mA and energy up to 1 MeV, normally operated with a 6-/spl mu/s macropulse and 12-Hz repetition rate. The beam loading and the energy spectra were measured to confirm the guns performance. The beam emittance was measured and compared with simulation results. The breakdown problem due to the field-emitted electrons and the backward electrons in the gun is discussed.

Beam Energy Drift and Energy Feedback System in the PLS 2.5GeV Linac

In PAL_XFEL, the specifications of the beam energy spread and rf phase are 0.03 %(rms) and 0.01 degrees(rms) respectively. We examined the rf performance in the present PLS 2.5 GeV Linac. The beam energy is changed as much as 0.8% by cooling temperature, air condition, and modulator high voltage jitter. The main factor to change the beam energy is the rf phase drift according to the variation of environmental condition. Dependence of the beam position drift on the rf phase was also examined. For the improvement of the injection beam stability, rf phase feedback system is designed and tested. This paper describes the rf phase feedback and the beam energy feedback system.

Status of the PAL-XFEL undulator program

Pohang Accelerator Laboratory (PAL) is developing 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 Xray undulator line requires 18 units of 5 m long hybrid-type conventional planar undulator and soft X-ray line requires 6 units of 5 m long hybrid type planar undulator with additional few EPUs for final polarization control. PAL is developing undulator magnetic structure based on EU-XFEL concepts. The key parameters are min pole gap of 8.3 mm, with period length 26 mm (HXU), 35 mm (SXU), and 5.0 m magnetic length. . In this report, the prototyping, and the development of pole tuning procedure, the impact of the background field error, and the effects of the girder bending on the optical phase error will be presented.

Measurement of isomeric yield ratios for Nb-93(gamma,4n)Nb-89m,Nb-g and Mo-nat(gamma,xn1p)Nb-95m,Nb-g reactions with 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios for the photonuclear reactions of 93Nb(γ,4n)89m,gNb and natMo(γ,xnp)95m,gNb by using the activation method. The high-purity 93Nb and natMo metallic foils in disc shape were irradiated with uncollimated bremsstrahlung beams of 50-, 60-, and 70-MeV generated from an electron linear accelerator in Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution γ-ray spectrometry with a calibrated high-purity Germanium (HPGe) detector coupled to a PC-based 4xa0K multichannel analyzer. The reaction 93Nb(γ,4n)89m,gNb was studied for the first time which has no comparable literature data. The result of 95m,gNb isomeric pair was measured based on (γ,p), (γ,np), and (γ,2np) reactions which is the first measurement at the intermediate energy region of 50–70-MeV with a natMo target.

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.