윤무현 교수

A four-sector 13-MeV cyclotron magnet, which does not employ the usual trim coils, was designed for positron-emission-tomography (PET) diagnostics. Instead, isochronism was achieved by placing a few side shims, as well as by slightly varying the vertical gap, along the radius of the cyclotron. The magnet was built based on the design, and its magnetic eld was measured using a Hall probe. Equilibrium orbits were computed using the measured data. Then, a series of systematic optimizations of the m

In this paper, we examine numerically and experimentally linear beam-optics distortion in the storage ring of the Pohang Light Source (PLS) and the correction of optics by using a number of quadrupole magnets installed in the storage ring. The measured orbit-response matrices were .tted to the model-response matrices to obtain . and the dispersion functions in the storage ring. By readjusting the currents of quadrupole-magnet power supplies, we were able to successfully restore the optics parame

In this paper, we examine the effect of the wakefields generated by an interaction between the circulating electron beam and the rf cavities and components of vacuum chambers on the longitu- dinal beam distribution, with particular emphasis on the Pohang Light Source (PLS) storage ring. In order to obtain an equilibrium longitudinal beam distribution for a single beam, we utilized both a numerical solution of the Vlasov equation and a multi-particle tracking method. Results show that the impedan

We used a streak camera to measure the longitudinal bunch shape of a circulating electron beam in the 2.5-GeV Pohang Light Source (PLS). The measured results were analyzed by an (R+L) series model to obtain a resistance R = 1.1 k­, an inductance L = 89 nH, and a longitudinal impedance jZ=njeff= 0.6 ­. The scaling law for the bunch lengthening is expressed as ¾l / I0:22§0:01. The eect of insertion device in the ring on the impedance, particularly the eect of the vertical height of the in-vacuum u

A next-generation synchrotron-radiation source planned at the Pohang Accelerator Laboratory (PAL) is described in this paper. It is a linac-based free electron laser (FEL) to produce an intense X-ray pulse down to a 0.1-nm wavelength with a 100-fs rms pulse length. This will make it possible for pump-probe experiments, such as dynamics studies of chemical reactions and coherent diffractive imaging, with a peak brilliance approximately ten orders of magnitude higher than that from the third-gener

A self-shielded four-sector 13-MeV cyclotron magnet has been designed for positron-emission tomography (PET). Compared with the previous one, which was built for the first time in Korea in 2003, this newly designed cyclotron is superior because it is compact and the stray field is reduced. An isochronous field was achieved by placing several side shims and by slightly varying the vertical magnet gap along the radius of the cyclotron. We show that the phase excursion is maintained within ±5 rf de

The equilibrium particle distribution of a bunch is investigated by using a localized δ 0 wake in an electron storage ring. A mapping method is performed to show the dynamical behavior of the particle distribution by using the Gaussian approximation. It is shown that stable multi-periodic states, a limit cycle, and chaos can exist under some conditions. When moving around the parameter space, the system can show bifurcation phenomena.

The fast-beam ion instability is a significant issue in an electron storage ring. In this paper, a weak-strong simulation code is used to simulate the fast-beam ion instability at the in-vacuum undulators of the Pohang Light Source (PLS) and the PLS-II. The growth time of the vertical oscillation amplitude is calculated for various vacuum pressures. Above the threshold vacuum pressure, the vertical oscillation amplitude exceeds the vertical beam size. The effect of a feedback system is investiga

LOCO (Linear Optics from Closed Orbit) is a tool to analyze linear beam-optics and search forerrors in the quadrupole focusing strength. Analysis with the help of LOCO reveals these errorsby fitting the measured orbit-response matrix to the model orbit-response matrix. By readjustingthe currents of the quadrupole-magnet power supplies to eliminate the magnet-gradient error, wecan bring the machine’s optics parameter close to the design values. In this paper, we use LOCOto show how the design bea

The electron cloud instability (ECI) is a signi¯cant issue at the International Linear Collider Damping Ring (ILC-DR) which can limit the performance. A new lattice called Cesr-TA has been developed from the Cornell Electron Storage Ring (CESR) for ILC-DR research. We investigate beam instabilities caused by the electron cloud in the Cesr-TA lattice. We simulate the interaction of a bunch and a cloud by using the uniform beta function lattice and the real lattice models of Cesr-TA. The simulatio

For a tightly focused laser, the beam-waist radius is of the same order as the wavelength and the lower-order-corrected Gaussian pulse description satisfies Maxwell's equations less accurately, so it becomes necessary to include all the field components that arise from the tight focusing of the laser so as to satisfy Maxwell's equations more accurately. The effect of the seventh-order-corrected chirped Gaussian laser beam on the electron acceleration in vacuum is investigated. A numerical simula

Research concern about neutron radiography has been increasing in Korea since 2001. Neutron radiography can help for the weakness of X-ray image. Neutron radiography can be used in not only non-destructive inspection but also basic science research. For those reasons more compact mono-energetic neutron source is needed. The 4 MeV deuteron cyclotron can be a candidate for the production of mono-energetic neutrons. In this paper optimal 4 MeV deuteron cyclotron magnet design is shown for neutron g

We show that a femto-second hard X-ray radiation pulse can be generated in a free-electronlaser amplifier without magnetic bunch compressors. This is possible by adopting a very lowcharge electron beam followed by the velocity bunching (VB) in two accelerating sections in alinear accelerator. With VB, an electron bunch with a bunch charge of 10 pC can be successfullycompressed in the presence of the space-charge effect by a factor of 150, from 0.2 ps to 1.3 fs rms. Multi-gigawatt hard X-ray radi