Tae-Yeon Lee

Measurement of storage-ring lattice functions: Application to the Pohang Light Source

Measurement of the lattice functions was carried out in the storage ring for the light source. The measurement includes β, dispersion functions, phase advances, tunes, momentum compaction, chromaticities, and linear coupling. Two methods were used for the β measurement; a quadrupole-tweaking method and a method using a sensitivity matrix. Using the sensitivity-matrix method gives additional information on the phase between monitors and correctors, as well as the fractional part of the tunes. The linear-coupling constant was obtained by driving the tunes across the coupling resonance and measuring the minimum tune separation. It is also shown that by using four skew-quadrupole circuits, the coupling constant can be varied arbitrarily. In this article, a detailed method for the lattice-function measurement is presented, and the result applied to the storage ring of the Pohang Light Source is given. The measured results are compared with the design values and shown to be in good agreement.

Gravitational spin–orbit coupling and the equivalence principle

Abstract The nonrelativistic Hamiltonian for a Dirac particle in the Schwarzschild space is compared with that in the frame with a constant acceleration a . The spin–orbit coupling − s ·( a × p )/(2mc 2 ) , in the accelerated frame, turns out to be the Thomas precession. But in the Schwarzschild Hamiltonian, in addition to the Thomas precession, there exists a gravitational spin–orbit coupling which seems to violate the Einsteins equivalence principle.

SU(2) gauge symmetry of a non-relativistic spin 1/2 particle

Abstract A non-relativistic quantum mechanical theory for a spin magnetic moment is constructed by quantizing the classical Hamiltonian based on the classical model of a magnetic moment as a localized current. It is shown that the electromagnetic interaction of a spin magnetic moment can be described by SU(2) gauge fields. It is argued that the quantum mechanical force is not gauge invariant and its classical limit can be obtained only at a fixed gauge.

Analysis of the Touschek lifetime and its application to the Pohang Light Source

The graph of measured beam lifetime as a function of time is analyzed based on the fact that the rate of change of the pure Touschek lifetime is exactly 1. The deviation from 1 of the rate of change of the measured beam lifetime is caused by the beam-gas scattering effect and the radiative electron beam polarization which can be expressed analytically. Comparing measured data with the analytic formulas, it is possible to estimate the beam-gas scattering lifetime and the polarization contribution to the beam lifetime. Further, it is possible to estimate the degree of polarization and its characteristic time constant.

Feasibility of a low-energy X-ray free-electron laser

X-ray free-electron lasers based on self-amplified spontaneous emission promise users unprecedented X-radiation that is extremely bright, extremely short and transversely coherent. However, hard X-ray free-electron laser facilities under construction are all huge and expensive, consisting of high-energy linear accelerators and long undulators. The benefit of hard X-ray free-electron lasers may be limited to only a few regions in the world, unless it is possible to reduce the size. This paper discusses how small a hard X-ray free-electron laser facility can be. It is shown that a 1.5 A X-ray free-electron laser is achievable using electron energy down to 4.5 GeV or lower if we use the third-harmonic radiation, but at the expense of the transverse coherence.

Transverse Mode Size in X-ray Free-Electron Laser

The transverse mode size of the X-ray free-electron laser is derived using information on transverse coherence. The derived formula for the mode size agrees well with the simulation result.

A method for deriving the Hamiltonians of insertion devices

Abstract Effects of wigglers and superconducting wigglers on the electrons in the storage ring are discussed based on the Hamiltonian formalism. In the local coordinates, it is useful to expand the wiggler field in the increasing order of the horizontal coordinate x , in which each coefficient of x n is itself an infinite polynomial of the vertical coordinate y . Combined with dimensional analysis, this expansion provides a simple and systematic approximation for normal wigglers of sinusoidal magnetic field. In the case of a non-analytic wiggler field as in superconducting wigglers, this method is still applicable with a little more care. In both cases, approximate Hamiltonians are derived.

Magnet lattice of the Pohang Light Source

Features of the 2-GeV Pohang Light Source Accelerator are described. The lattice type is Tripple Bend Achromat (TBA). The whole circumference of 280.56 m is composed of 12 cells each of which has 12 quadrupoles. The harmonic number is 468 (=2/sup 2/*3/sup 2/*13) and the corresponding RF frequency is 500.082 MHz. The aimed natural emittance is 12 nm-rad. The description is mainly concerned with lattice properties and insertion device (ID) effects.<<ETX>>

Loss minimizing gear shifting algorithm based on optimal current sets for IPMSM

Two speed gear is preferable in the commercial EVs such as EV trucks and EV bus, since they require a high starting torque and high speed driving, too. In this work, two speed gear with 12.5∶1 and 5∶1 is considered. The wheel torque is mapped to different points in the torque-speed plane of the motor depending on the reduction ratio. To determine the efficiency, it is necessary to calculate the losses for the two cases. To be fair, optimal current set (id, iq) should be found for each case before calculating the loss, since the copper and inverter losses depend heavily on the current magnitude. The operation points are found by the MTPA method, or at the intersection between the torque and voltage limit curve. Ferraris method is utilized to solve the fourth order equation resulted from the intersection. After comparing the losses for different gear ratios, the wheel torque-speed plane is separated, and from which an optimal gear shifting algorithm is developed. Simulation was performed by using NEDC. The results show that the proposed gear shift algorithm is superior to a fixed gear in minimizing the loss.

Implications of the Differential Equations of the X-ray Free-Electron Laser

Differential equations governing the X-ray free-electron laser are complicated and it is not straightforward to see all the information they have other than the fitting formula for the radiation power gain. Using the equations and the fitting formula but not solving the equations completely, some useful information is obtained including the radiation beam size and the saturation value of the bunching parameter.