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Extraction mirrors installed at the most upstream position of interferometry beam size monitor are frequently used for measuring the beam size in storage rings. These mirrors receive the high power synchrotron radiation and are distorted owing to the heat distribution that depends on the position on the mirror surface. The distortion of the mirror changes the effective separation of the slit in the interferometry beam size monitor. Estimation of the effects of the front-end mirror distortion is important for measuring the beam size accurately. In this paper, we present the result of the numerical simulation of the temperature distribution and thermal expansion of the front-end mirror using ANSYS code, the theoretical basis of the effects of mirror distortion and compare with experimental results from Pohang Light Source II (PLS-II) at the Pohang Accelerator Laboratory (PAL). The equipment in the beam diagnosis line in PLS-II and experimental set-up for measuring the distortion of the front-end mirror using a multi-hole square array Hartmann screen are described. [ABSTRACT FROM AUTHOR]

We present a lattice design for a low-emittance and high-brilliance 3 GeV synchrotron light source that has been widely investigated in the world. We show the design results for a MBA (Multi-Bend Achromat) lattice with an emittance of 1.3 nm and 282.4 m circumference. Each cell has 5 bending magnets that consist of outer two with bending angle of 4.5° and inner three with bending angle of 7°. The lattice is designed to be flexible and consists of 12 straight sections in which one straight section has a length of 5.9 m. We have studied the dynamic aperture in the lattice with machine errors. It is shown that the designed low-emittance lattice provides sufficient dynamic aperture after COD correction. We present the results of variations of emittance, energy spread and dynamic aperture due to in-vacuum undulators in the straight sections. We performed particle tracking after the beam injection to investigate the efficiency of the injection scheme. We show the designed results of an injection scheme that shows the space allocation in injection section and the particle motions of injected beam. Our designed lattice provides a good optimization in terms of the emittance and brilliance as a light source for 3 GeV energy and circumference of 28 m. [ABSTRACT FROM AUTHOR]

Abstract: For a future synchrotron light source based on a linac, e.g. an X-ray free electron laser and an energy recovery linac (ERL), an injector is a key component to generate a high brightness electron beam. For the acceleration and transportation of the electron beam in the injector, the adjustment of beam orbit inside the cavity is important to avoid the deterioration of the beam quality due to the transverse electric field of it, which causes the transverse emittance growth. To adjust the beam orbit, an investigation of the electromagnetic center of the cavity is required in the beam operation. This paper shows a new method for measuring the electromagnetic center of the cavity, and describes an analytical model of emittance growth due to a combination of transverse electric field and orbit offset. The validation of the method was confirmed by the emittance measurement in the compact ERL (cERL) injector at KEK. [Copyright &y& Elsevier]

Abstract: The Energy Recovery Linac (ERL) is one of the candidates for the next generation light sources, which is based on the 1.3GHz superconducting radio frequency (SRF) linear accelerator. The ERL can produce high brilliance synchrotron radiation and a short pulse beam. We investigated the beam dynamics in the compact-Energy Recovery Linac (c-ERL) with a beam energy of 35MeV, which is a prototype of the 5GeV ERL at KEK. One of the main goals of our studies on the c-ERL is the emittance compensation in the merger section to achieve an emittance smaller than 1.0mmmrad. In the case of the early commissioning phase, the injector system produces electron bunches of 5MeV with a repetition rate of 1.3GHz. The compensation of the emittance growth due to the space charge effect was investigated in order to achieve a small emittance at the exit of the merger. We discuss the results of a method to compensate the emittance growth which is based on beam envelope matching between the betatron function and the linear dispersion induced by the space charge force. We investigated the space charge effect when the beam energy in the superconducting RF section was changed. The effect of space charge in the arc section was also investigated. It is shown that the space charge effect in the c-ERL is an important source of distortion of the optics function. In this paper, we show the results on the analysis of the effect of space charge in the compact-ERL at KEK which has a low-energy beam. [Copyright &y& Elsevier]

We investigated optimum choices of beam and accelerator parameters for low-charge beams of self-amplified spontaneous emission (SASE) free-electron laser (FEL) at PAL. The FEL system is designed to provide a short pulse beam to generate the high power of the wavelength of 1-\\rm\AA in the undulator. The designed linac provides the pulses of 10 fs rms and 3.85 fs rms for the charges of 0.2 nC and 0.02 nC, respectively. Parameters of the two-stage bunch compressors are optimized to reduce the effects of coherent synchrotron radiation. The bunch compressors are also designed such that the effects of nonlinearities due to wakefields, rf curvature, and second-order momentum compaction become as small as possible in the linear accelerator. Through these parameter optimizations, we have minimized the bunch charges that could decrease effects of emittance dilution and growth of energy spread, which may deteriorate the SASE performance. Start-to-end tracking simulations include the longitudinal and transverse wakefields, and the effects of errors such as rf gun timing, rf phase, and rf voltage are investigated. We investigated the effectiveness of a laser heater that may give Landau damping to suppress the microbunching beam instability. It is shown that a laser heater may suppress the microbunching beam instability in the FEL system. We also investigated the effects of the ac and dc resistive wall wakefields in a long undulator. It is shown that energy variations induced within the bunch over the length of the undulator are acceptable. As a result, through these optimizations studies, we could get beam parameters and accelerator parameters that can provide the FEL power of the 60 GW with FEL pulse of 10 fs and 3 fs in the wavelength of 1-\\rm\AA in around a 50-m-long undulator for the charges of 0.2 nC and 0.02 nC, respectively. It is shown by our optimizations that our designed FEL system shows required performances for the low-charge beams in the 10 GeV. [ABSTRACT FROM PUBLISHER]