Tong-Nyong Lee

The Pohang light source

A 2 GeV synchrotron light source project is in progress in Pohang, Korea. The light source is designed to provide high brightness radiation with continuous wavelengths down to 1 A (10-8 em) with its peak at 4·43 A(Le. 2·8 keY). The project, consisting of a full energy injector linear accelerator and a 2 GeV storage ring, was launched in 1988 and is scheduled to be completed by the end of 1994. In this article, we introduce the main features and status of the storage ring components and the installation procedure. Radiation characteristics and beamline status are also described.

Performance of the Pohang Light Source

Abstract The Pohang Light Source has actively supported users since the commissioning in 1994. In 1999, we had two decisive breakthroughs for the machine performance; installation of feedback systems to actively damp the coupled-bunch instabilities, and 2.5 GeV operation through energy ramping of the 2.0 GeV electron beam from the linac. Now we can provide two stable operation modes, 2.0 and 2.5 GeV modes. This paper describes the upgraded machine performance and the beamline status of the Pohang light source. Having started with two beamlines in 1995, the facility now has 12 beamlines operational, 1 beamline under commissioning, and 7 beamlines under construction.

Chirped femtosecond pulse scattering by spherical particles

Generalized Lorentz-Mie formulas are used to study the scattering characteristics when a chirped femtosecond pulse illuminates a spherical particle. For a linear chirped Gaussian pulse with the envelope function g(τ) = exp[-π(1 + ib)τ(2)], dimensionless parameter b is defined as a chirp. The calculation illustrated that even for pulses with a constant carrier wavelength (λ(0) = 0.5 µm) and pulse-filling coefficient (l(0) = 1.98), the efficiencies for extinction and scattering differ very much between the carrier wave and the different chirped pulses. The slowly varying background of the extinction and the scattering curves is damped by the chirp. When the pulse is deeply chirped, the maxima and minima of the background curves reduce to the point where they disappear, and the efficiency curves illustrate a steplike dependence on the sphere size. Another feature is that the chirped-pulse scattering seems blind: it depends only on the amount of chirp (|b|), regardless of upchirp (b > 0) or downchirp (b< 0).

Comparison of x-ray lasers and third-generation synchrotron radiation sources

There exist some overlapping areas of research in the development of x-ray-lasers and synchrotron radiation sources. In this report, we compare the characteristics and applications of the currently available x-ray lasers and the third-generation synchrotron radiation.

Space‐resolved extreme ultraviolet (XUV) spectroscopy using a toroidal mirror

In order to collect radiation from a distant light source and to compensate astigmatism, a toroidal mirror is often placed in front of a grazing‐incidence spectrograph. In this study, characteristics of space‐resolved spectra obtained with such a system have been investigated using a ray‐tracing analysis. The following was found: in the stigmatic focal region of the spectrum, the spatial resolution along the sagittal direction is excellent but that along the meridional direction is poor; on the other hand, in the astigmatic wavelength region, the trend is reversed, i.e., the spatial resolution along the sagittal direction is poor but that along the meridional direction is good, particularly in the wavelength region which is far from the stigmatic focus. The method was successfully applied to the space‐resolved spectroscopic study of a capillary discharge plasma.

Commissioning of the PLS 2 GeV storage ring

In Pohang, Korea, construction of a third-generation 2 GeV light source has been in progress since 1988. Installation of the storage ring components started in March 1993 and was completed in August 1994. Initially, only two super-periods out of 12 were baked out in-situ. From September to the end of 1994, the machine commissioning had been carried out. The initial injection energy for the commissioning was chosen to be 1.4 GeV because at this energy the injection kicker magnet can make a design bump, -21 mm. On September 8, the injected beam from the injector linear accelerator was circulated in storage ring more than 500 turns without RF. After accumulating the beam up to 76 mA on October 20, the injection energy was changed to the design value which is 2.0 GeV. At 2.0 GeV, amount of the bumped orbit which the kicker magnet can generate is -15 mm. Additional -6 mm bump is produced by four horizontal corrector magnets located on each side of the injection straight section. On December 24, 1994, the beam was stacked up to 300 mA, exceeding the commissioning goal of 100 mA. From January to March 1995, the ring had been shut down for in-situ bakeout. Since April, the second commissioning has been in progress. The PLS facility will be open to users in July 1995. In this paper, we present the current status of the PLS storage ring commissioning and the future plan for normal operation.

Soft x‐ray lasing in a capillary discharge

Soft x‐ray lasing in the C VI Balmer α transition is observed in a capillary discharge. The capillary is made of polyethylene with a bore diameter of 1.2 mm. Plasma radiation from the discharge is analyzed using a toroidal mirror and a two‐meter grazing‐incidence spectrograph‐monochromator. The electron temperatures are measured at both the axial and the peripheral region close to the capillary wall, using space‐resolved spectra. A comparison of the branching ratio in the hot (axial) and the cool (peripheral) plasma regions indicates that there is a large population inversion between n=3 and 2 states of C5+ ions in the cool (Te∼13 eV) region of the capillary plasma. Relative line intensities of the C VI Hα and a number of non‐lasing lines are compared in this cool region as a function of capillary length. The C VI Hα line intensity increases exponentially whereas those of non‐lasing transitions increase linearly with an increase of the capillary length. The gain coefficient thus measured indicates 2.8 cm−...

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.

Optimization of EPU6 undulator at PLS

Pohang Accelerator Laboratory (PAL) is developing an Elliptically Polarized Undulator (EPU) to produce polarized synchrotron radiation at Pohang Light Source (PLS). The EPU6 is an Apple-II type elliptical undulator, which changes the polarization of the field by translating the quadrant arrays. The PLS EPU6 features a period of 6 cm, a minimum gap of 19 mm, 25 full field periods, a maximum vertical flux density of 0.69 T, a maximum horizontal flux density of 0.46 T, and 1575 mm total magnetic structure length. The EPU6 is optimized for highly polarized synchrotron radiation from 117 to 1500 eV at 2.5 GeV electron energy. Using correction coils to compensate the orbit drift in the undulator increased the estimated photon flux by 15% compared to the case without the compensation.

Status of the Pohang light source project

Abstract The Pohang Light Source is a third-generation synchrotron radiation facility currently under construction in Pohang, Korea. It consists of a 2 GeV full energy injection linac, a storage ring, and three initial beamlines. Construction of the conventional facility is now nearly completed and the machine integration of the linac and the storage ring is well under way. The commissioning is scheduled to take place toward the fall of 1994, and it will be opened to national as well as international users by mid-1995. The facility will eventually furnish high-brightness sources of radiation utilizing 22 bending magnets and 10 insertion devices. Characteristics of the design and beamlines under construction will be described.