Takemasa Masuda

Bio: Takemasa Masuda is an academic researcher. The author has contributed to research in topics: Free-electron laser & SACLA. The author has an hindex of 4, co-authored 5 publications receiving 1723 citations.

A compact X-ray free-electron laser emitting in the sub-ångström region

Abstract: Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

A compact free-electron laser for generating coherent radiation in the extreme ultraviolet region

Abstract: Single-pass free-electron lasers based on self-amplified spontaneous emission1,2,3,4 are enabling the generation of laser light at ever shorter wavelengths, including extreme ultraviolet5, soft X-rays and even hard X-rays6,7,8. A typical X-ray free-electron laser is a few kilometres in length and requires an electron-beam energy higher than 10 GeV (refs 6, 8). If such light sources are to become accessible to more researchers, a significant reduction in scale is desirable Here, we report observations of brilliant extreme-ultraviolet radiation from a 55-m-long compact self-amplified spontaneous-emission source, which combines short-period undulators with a high-quality electron source operating at a low acceleration energy of 250 MeV. The radiation power reaches saturation at wavelengths ranging from 51 to 61 nm with a maximum pulse energy of 30 µJ. The ultralow emittance (0.6π mm mrad) of the electron beam from a CeB6 thermionic cathode9 is barely degraded by a multiple-stage bunch compression system that dramatically enhances the beam current from 1 to 300 A. This achievement expands the potential for generating X-ray free-electron laser radiation with a compact 2-GeV machine. Free-electron lasers can produce powerful pulses of radiation at very short wavelengths, even in the hard-X-ray region. In general, however, they comprise facilities several kilometres in length. A 55-m-long laser could open up the technology to a broader range of researchers.

Stable operation of a self-amplified spontaneous-emission free-electron laser in the extremely ultraviolet region

Abstract: We achieved stable operation of a free-electron laser (FEL) based on the self-amplified spontaneous-emission (SASE) scheme at the SPring-8 Compact SASE Source (SCSS) test accelerator in the extremely ultraviolet region. Saturation of the SASE FEL power has been achieved at wavelengths ranging from 50 to 60 nm. The pulse energy has reached $\ensuremath{\sim}30\text{ }\text{ }\ensuremath{\mu}\mathrm{J}$ at 60 nm. The observed fluctuation of the pulse energy is about 10% (standard deviation) for several hours, which agrees with the expectation from the SASE theory showing the stable operation of the accelerator. The SASE FEL has been routinely operated to provide photon beams for user experiments over a period of a few weeks. Analysis on the experimental data gave the normalized-slice emittance at the lasing part is around $0.7\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$. This result indicates that the normalized-slice emittance of the initial electron beam, $0.6\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ in a 90% core part, is kept almost unchanged after the bunch compression process with a compression factor of approximately 300. The success of the SCSS test accelerator strongly encourages the realization of a compact XFEL source.

RF System of the SPring-8 Upgrade Project

Abstract: In the upgrade project of the SPring-8 storage ring, a beam energy is lowered from 8 to 6 GeV. The upgrade employs multi-bending optics to have a beam emittance of approximately 100 pm.rad and shortens the straight sections available for RF accelerating cavities by 30%. The total 16 bell-shaped single-cell cavities are installed in the sections and generate a needed accelerating voltage of 7 MV. The old-fashioned analogue LLRF system in use is to be replaced with a compact digital system based on the under-sampling scheme and the MTCA.4 standard. The SACLA linac is to be used as an injector of a lowemittance beam to the ring. We build a timing system to inject the beam to a target bucket-position in the ring within a time deviation of 3 ps. Since the X-ray FEL operation and the beam injection must be balanced on demand, a pulse-by-pulse control system for beam parameters of SACLA is going to be implemented to the SACLA LLRF system.

Development of a Linac for Injection of Ultrashort Electron Bunches Into Laser Plasma Electron Accelerators

Abstract: We are developing a C-band linac that produces ultrashort electron bunches as an injector for laser plasma accelerators to study their acceleration characteristics for realizing practical ultrasmall electron accelerators. We designed a linac to produce electron bunches with a longitudinal length of less than 10 fs and transverse dimensions less than 100 m for injection into a proper phase of the laser plasma acceleration field. An RF gun and a buncher tube were precisely manufactured and they satisfied the designed performance producing the ultrashort electron bunches. Synchronizing electron bunch injection and plasma wave excitation requires a highly accurate timing control within 10 fs. An RF master oscillator with a single sideband phase noise of -150 dBc/Hz at 10 MHz has been developed for precise synchronization. A power supply for the klystron to generate a high power RF was also developed, which provides a 350 kV voltage pulse with a voltage jitter of 3.16 ppm. The power and phase stability performances achieved above the world's highest level. INTRODUCTION Particle accelerators are important tools for scientific discovery and medical treatment. However, their size and construction budget are large. Then, the accelerators cannot be widely used in small factories and hospitals in spite of their usefulness. It is strongly required to reduce the size and costs of the accelerators to fit into factory production lines or hospital operating rooms. A high intense ultrashort laser pulse propagating in a plasma can excite a large amplitude traveling plasma wave with a phase velocity equivalent to a group velocity of the laser pulse at almost the speed of light in a vacuum. This plasma wave can trap and accelerate electrons. The laser plasma electron acceleration [1] has the potential to surpass the performance of the conventional RF accelerators because its acceleration gradient is of the order of 1000 times larger than that of the conventional one. So far, some laser plasma acceleration experiments with an acceleration length of less than a few 10 cm demonstrated the generation of electron beams with a peak energy of around 10 GeV and an energy spread of less than 10% [2]. However, stability of beam parameters, such as an energy spectrum, an emission direction, a beam divergence, a beam charge, and so on are still not sufficient as the practical accelerator. To solve this problem, it is essential to clarify the details of the phase space of the plasma wave acceleration field. However, it has not been sufficiently and experimentally investigated. The Japan Science and Technology Agency (JST)’s Mirai Program [3] is conducting research aimed at demonstrating a small electron accelerator based on a laser plasma acceleration. Japan Synchrotron Radiation Research Institute (JASRI), which is one of the agencies for this project, is developing a linear accelerator based on the conventional radio frequency (RF) technology. This linac will be used as an ultrashort electron bunch injector into the laser plasma acceleration field. We aim to map the acceleration characteristics of the plasma wave by generating a highly stable electron beam and scanning the electron beam in the vertical, horizontal, and longitudinal positions with respect to the phase space of the plasma wave to reveal the above detail. Such an experiment has not been conducted so far. This paper reports the current status of the development of the ultrashort electron bunch linac. DESIGN AND OUTLINE OF ULTRASHORT BUNCH ELECTRON LINAC Because the plasma wave has a wavelength typically of the order of 10 to 100 fs, an injected electron bunch length must be less than 10 fs. In addition, the transverse dimensions of a planned plasma wave are typically the order of 10 to 100 m because that is the same order of a transverse laser spot size. The transverse dimensions of the injected electron bunch also must be smaller than those of the plasma wave. There are three possible methods to generate ultrashort electron bunches with a length of less than 10 fs. (1) The first method is using a photocathode RF gun driven by ultrashort laser pulses. However, there is no scientific evidence to generate a bunch of less than 10 fs directly from the cathode, and a long-term study should be needed to show the evidence. (2) The second is to use a magnetic chicane composed of dipole magnets to compress the energy chirped electron bunch [4]. This requires high costs and large components for the chicane. (3) The third we chose is to use an acceleration tube as a buncher to compress the electron bunch by using velocity bunching [5, 6]. Costs are lower than the second and components are not so large as the second. 12th Int. Particle Acc. Conf. IPAC2021, Campinas, SP, Brazil JACoW Publishing ISBN: 978-3-95450-214-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2021-WEPAB055 MC2: Photon Sources and Electron Accelerators A08 Linear Accelerators WEPAB055 2725 C on te nt fr om th is w or k m ay be us ed un de rt he te rm s of th e C C B Y 3. 0 lic en ce (© 20 21 ). A ny di st ri bu tio n of th is w or k m us tm ai nt ai n at tr ib ut io n to th e au th or (s ), tit le of th e w or k, pu bl is he r, an d D O I

First lasing and operation of an ångstrom-wavelength free-electron laser

Abstract: The Linac Coherent Light Source free-electron laser has now achieved coherent X-ray generation down to a wavelength of 1.2 A and at a brightness that is nearly ten orders of magnitude higher than conventional synchrotrons. Researchers detail the first operation and beam characteristics of the system, which give hope for imaging at atomic spatial and temporal scales.

A compact X-ray free-electron laser emitting in the sub-ångström region

Abstract: Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

Theory and Design of Charged Particle Beams

Abstract: Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

Phase Retrieval with Application to Optical Imaging: A contemporary overview

Abstract: i»?The problem of phase retrieval, i.e., the recovery of a function given the magnitude of its Fourier transform, arises in various fields of science and engineering, including electron microscopy, crystallography, astronomy, and optical imaging. Exploring phase retrieval in optical settings, specifically when the light originates from a laser, is natural since optical detection devices [e.g., charge-coupled device (CCD) cameras, photosensitive films, and the human eye] cannot measure the phase of a light wave. This is because, generally, optical measurement devices that rely on converting photons to electrons (current) do not allow for direct recording of the phase: the electromagnetic field oscillates at rates of ~1015 Hz, which no electronic measurement device can follow. Indeed, optical measurement/detection systems measure the photon flux, which is proportional to the magnitude squared of the field, not the phase. Consequently, measuring the phase of optical waves (electromagnetic fields oscillating at 1015 Hz and higher) involves additional complexity, typically by requiring interference with another known field, in the process of holography.

Highly coherent and stable pulses from the FERMI seeded free-electron laser in the extreme ultraviolet

Abstract: Researchers demonstrate the FERMI free-electron laser operating in the high-gain harmonic generation regime, allowing high stability, transverse and longitudinal coherence and polarization control.