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In recent years, there have been several projects in the world to design and construct a diffraction-limited light source which pushes an emittance of electron beams in a storage ring close to an emittance of photon beams in the X-ray region to enhance brilliance by two orders of magnitude. In line with this trend, the Korea fourth-generation storage ring (Korea-4GSR) project was launched in 2021 to establish a new light source in the Republic of Korea with an ultra-low emittance of 50 pm rad at a beam energy of 4 GeV. For the Korea-4GSR project, a compact linear accelerator for generating 200 MeV and a booster synchrotron is chosen as an injector. The booster synchrotron ramps beam energy from 200 MeV to 4 GeV and the lattice is designed based on the FODO concept. It is crucial in the booster to achieve high beam quality for injection efficiency into a storage ring. Since the quality of the extracted beam relies on an energy ramping profile, the ramping process is important to be optimized. This paper represents the result of our studies on the effect of the energy ramping profile in the evolutionary physical process in a booster synchrotron. [ABSTRACT FROM AUTHOR]

We investigated optimum choices of accelerator parameters for superconducting-technology-based heavy-ion linear accelerator (linac) to achieve the high beam quality at an in-flight target with a high beam power of 400 kW. The superconducting linac system is designed to provide a stable-ion beams from protons to uranium with energies of 600 MeV and 200 MeV/u, respectively. The linac optics is also designed such that the effects of envelope instability, parametric resonance between the transverse and longitudinal planes, beam steering effect due to asymmetric field in quarter-wave resonance (QWR) cavities, and emittance growth in charge strippers due to the straggling effect, parametric resonance, and envelope instability become as small as possible. The dimensions of the warm and cold sections in the low-energy section which mainly determine the longitudinal acceptance of the linac are optimized to achieve a longitudinal acceptance larger than 27 keV/u-ns enabling stable operation. The tracking simulation for the uranium beam was performed and we achieved the transverse normalized rms emittance of 0.095 mm-mrad and longitudinal rms emittance of 2.10 keV/u-ns at the end of designed linac without uncontrolled beam losses along the linac. In order to estimate the degradation of the machine performance due to imperfections such as misalignment, ripple of the magnet power source, and phase and power variation of the RF source, the particle tracking simulation was performed and the uncontrolled beam loss with the machine imperfection without the orbit and optics correction was less than 1 W/m which is a condition required for machine operation. The optimum scheme for orbit correction in the low-energy linac is investigated based on the transfer matrix of the elements and the validation of the scheme is confirmed by the particle tracking simulation using TRACK code. [ABSTRACT FROM PUBLISHER]

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]

Numerical simulation studies are performed for the proposed infrared self-amplified spontaneous-emission free-electron laser (SASE-FEL) at the existing PLS test linac. It is shown that a high-gain SASE-FEL with a 1.5 μm radiation wavelength could be driven by a 61-MeV electron beam from the S-band rf linac and a 5-m long undulator. Third-harmonic generation to 0.5 μm radiation wavelength was also investigated to enhance the usefulness of the infrared SASE-FEL facility. Bunching fractions of the nonlinear third harmonic to the fundamental mode in the designed SASE-FEL is estimated and showed that the third-harmonic emission resulted in the same trend as the fundamental. This paper attempts to investigate the effect of the beam parameters such as the emittance, the energy spread, the beam energy, and the peak beam current to the designed infrared SASE-FEL. The wake effects due to the surface roughness of beam chamber in the undulator are also estimated. [Copyright &y& Elsevier]

We demonstrate an experimental methodology for measuring the temporal distribution of pico-second level electron bunch with low energy using radial electric and azimuthal magnetic fields of an accelerating ( TM 01 mode) radio frequency (RF) cavity that is used for accelerating electron beams in a linear accelerator. In this new technique, an accelerating RF cavity provides a phase-dependent transverse kick to the electrons, resulting in the linear coupling of the trajectory angle with the longitudinal position inside the bunch. This method does not require additional devices on the beamline since it uses an existing accelerating cavity for the projection of the temporal distribution to the transverse direction. We present the theoretical basis of the proposed method and validate it experimentally in the compact-energy recovery linac accelerator at KEK. Measurements were demonstrated using a 2-cell superconducting booster cavity with a peak on-axis accelerating field ( E 0 ) of 7.21 MV/m. [ABSTRACT FROM AUTHOR]