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京都大学0048新制・課程博士博士(理学)甲第11852号理博第2945号新制||理||1441(附属図書館)23632UT51-2005-N686京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 西川 公一郎, 教授 今井 憲一, 助教授 中家 剛学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

Timing and low-level rf system for an x-ray laser

An x-ray free-electron laser (XFEL), SACLA, designed to open up new science, was constructed for generating coherent x rays with a peak power of more than 10 GW and a very short pulse of below 30 fs. This feature demands a very highly short-term temporal stability of less than 50 fs to the acceleration rf field of SACLA. For this reason, we developed a timing and low-level rf (LLRF) system for SACLA based on that of the SPring8 compact SASE source (SCSS) test accelerator for verifying the feasibility of an XFEL. The performance of the system using the in-phase and quadrature rf manipulation method was improved from SCSS’s system. Since the facility length of SACLA is 700 m, which is 10 times longer than that of the SCSS test accelerator, a phase-stabilized optical-fiber system designed to transmit time standard rf signals with low loss was also developed and deployed. This optical-fiber system equips fiber optical-length feedback control in order to mitigate environmental effects, such as temperature and humidity changes. On the other hand, the demanded maximum rf temporal stability is less than 50 fs, which is almost 10 times smaller than that of the SCSS test accelerator. Hence, reducing electric noise and increasing the temperature stability around timing and LLRF instruments were necessary and realized with a very low-noise power supply and a hemathermal 19-inch enclosure. The short-term temporal performance of the timing LLRF system finally attained a temporal stability of less than 13.6 fs in rms measured by a beam arrival-time measurement. This stability greatly helps to achieve the stable x-ray lasing of SACLA for routine operation during user experiments

Brightness analysis of an electron beam with a complex profile

We propose a novel analysis method to obtain the core bright part of an electron beam with a complex phase-space profile. This method is beneficial to evaluate the performance of simulation data of a linear accelerator (linac), such as an x-ray free electron laser (XFEL) machine, since the phase-space distribution of a linac electron beam is not simple, compared to a Gaussian beam in a synchrotron. In this analysis, the brightness of undulator radiation is calculated and the core of an electron beam is determined by maximizing the brightness. We successfully extracted core electrons from a complex beam profile of XFEL simulation data, which was not expressed by a set of slice parameters. FEL simulations showed that the FEL intensity was well remained even after extracting the core part. Consequently, the FEL performance can be estimated by this analysis without time-consuming FEL simulations

Construction of Beam Monitor Control System for Beam Transport From SACLA to SPring-8

In a part of the SPring-8 upgrade project, the SACLA linac will be used as the injector for the SPring-8 storage ring. We will upgrade the beam monitor system for beam transport, which consists of screen monitor (SCM), beam position monitor (BPM) and current monitor (CT). For the SCM, we adopted GigE Vision standard for the CCD camera and EtherCAT as a field bus for the stepper motor control of focusing system. We have developed camera control software using open source libraries to integrate various vendors’ GigE Vision cameras with the SPring-8 control framework. A grabbed image is stored into the file server and property, such as camera settings for image and event number, is stored into the database. The BPM is a key device for precise and stable injection. We adopted the commercially available MTCA.4 fast ADC/DAC module with modified firmware developed for readout of the BPM and the CT. We are developing acquisition software for MTCA.4 modules to synchronize with a beam trigger. The acquired data are stored into the database with time stamp and event number. We present the preparation of beam monitor control system for the beam transport to injection from SACLA to SPring-8

VARIATION OF BEAM ARRIVAL TIMING AT SACLA

Abstract SPring-8 Angstrom Compact Laser (SACLA) is a XFEL facility which provides intense pulsed X-ray laser to various scientific fields. It is a key issue to deliver stable timing signals to the accelerator components, the beam monitor units and apparatus of XFEL users with a precision of less than 100 fs RMS. Since the arrival timing of the X-ray at an experimental station depends on that of the electron beam, we measured the arrival timing of the electron beam by comparing a reference rf signal and a beam induced signal from an rf beam position monitor (RF BPM). A jitter of the arrival timing monitor was 41 fs in RMS calculated from a correlation plot of two adjacent BPMs data. To evaluate the stability of the timing monitor, we measured the difference of the arrival timings between two BPMs located at the entrance and the exit of the BL3 section. The difference of the arrival timings was about 180 fs pk-pk for 2 days measurement, which is the present accuracy of our beam arrival timing monitor

High peak current operation of x-ray free-electron laser multiple beam lines by suppressing coherent synchrotron radiation effects

The parallel operation of multiple beam lines is an important means to expand the opportunity of user experiments at x-ray free-electron laser (XFEL) facilities. At SPring-8 Angstrom free-electron laser (SACLA), the multi-beam-line operation had been tested using two beam lines, but transverse coherent synchrotron radiation (CSR) effects at a dogleg beam transport severely limited the laser performance. To suppress the CSR effects, a new beam optics based on two double bend achromat (DBA) structures was introduced for the dogleg. After the replacement of the beam optics, high peak current bunches of more than 10 kA are now stably transported through the dogleg and the laser pulse output is increased by a factor of 2–3. In the multi-beam-line operation of SACLA, the electron beam parameters, such as the beam energy and peak current, can be adjusted independently for each beam line. Thus the laser output can be optimized and wide spectral tunability is ensured for all beam lines

Time-interleaved multienergy acceleration for an x-ray free-electron laser facility

To meet the demand from the growing number of user experiments, multi-beam-line operation with a wide spectral range is seriously considered in x-ray free-electron laser facilities. In a conventional design, the beam line of low photon energies branches off from the middle of the accelerator to take out low energy electron beams. Here in this paper, a novel method is proposed to deliver bunch-to-bunch energy changed electron beams at the end of the accelerator. Since all accelerator components are operated in steady state, this method enables quasisimultaneous operation of multi-beam-line in the same undulator hall without degrading the stability and performance of the electron beam

Low-emittance thermionic-gun-based injector for a compact free-electron laser

A low-emittance thermionic-gun-based injector was developed for the x-ray free-electron laser (XFEL) facility known as the SPring-8 angstrom compact free-electron laser (SACLA). The thermionic-gun-based system has the advantages of maintainability, reliability, and stability over a photocathode radio-frequency (rf) gun because of its robust thermionic cathode. The basic performance of the injector prototype was confirmed at the SPring-8 compact self-amplified spontaneous emission source (SCSS) test accelerator, where stable FEL generation in an extreme ultraviolet wavelength range was demonstrated. The essential XFEL innovation is the achievement of a constant beam peak current of 3–4 kA, which is 10 times higher than that generated by the SCSS test accelerator, while maintaining a normalized-slice emittance below 1 mm mrad. Thus, the following five modifications were applied to the SACLA injector: (i) a nonlinear energy chirp correction; (ii) the optimization of the rf acceleration frequency; (iii) rf system stabilization; (iv) nondestructive beam monitoring; and (v) a geomagnetic field correction. The SACLA injector successfully achieved the target beam performance, which shows that a thermionic-gun-based injector is applicable to an XFEL accelerator system. This paper gives an overview of the SACLA injector and describes the physical and technical details, together with the electron beam performance obtained in the beam commissioning