Plans are underway for the upgrade of the SPring-8 facility, targeting completion in the early 2020’s. Sustainability is a key guiding principle for the fourth-generation X-ray source a beam emittance of around 100 pm.rad is pursued simultaneously with substantial energy-saving. The five key concepts enabling the above scenario are (i) to set the proper beam performance taking account of a role of the fourth generation source in the X-ray source evolution, (ii) to adopt advanced undulator technologies for the total system optimization, (iii) to reduce the power consumption as much as possible by reasonably integrating innovative designs and technologies, (iv) to utilize the SACLA linac as an injector to the upgraded ring for the high performance operation, and (v) to minimize the blackout period for quick restart of the user operation.

SPring-8 Upgrade Project

An ultra-high-speed short pulse switch for high power devices has been developed by using SiC MOSFET which is one of the next generation semiconductors. Semiconductor switches using SiC-MOSFETs are expected to substitute the thyratron, and they are designed by connecting many semiconductor switches in parallel-series for high power operation. In order to suppress the commonmode noise caused by switching, it is common to form a symmetrical circuit. However, as the number of parallel connections in the horizontal direction increases, the length of the parallel circuit becomes longer, and the output waveform is distorted due to time lag between the circuits. Therefore, we propose a radially-symmetrical type module switch which can equalize the circuit length regardless of the number of parallel circuit. The design and preliminary test results of two types of switch circuits, radially-symmetrical type and general line-symmetrical type are presented here. INTRODUCTION Transistors such as Si diodes, MOSFETs (Metal-OxideSemiconductor Field-Effect Transistor) and IGBTs (insulated gate bipolar transistors) are used as power elements [1]. The development of next generation semiconductors aimed at improving the performance of the power semiconductor is thriving. One of them is SiC (silicon carbide). SiC power semiconductors can realize "high withstand voltage", "low on resistance", "small switching loss". However, the current SiC device is in the process of development and has high withstand voltage but does not support high current. For this reason, in order to realize the semiconductor switch for high current power supply etc., it is absolutely necessary to construct a circuit by parallel multiplexing of elements [2-4]. Regarding multiplexing circuits of semiconductor switches, the usefulness of symmetric circuits has been confirmed as a method of reducing a commonmode noise caused by switching [5]. However, when the number of parallel connections is increased, since a large number of elements are arranged side by side, the length of the parallel circuit becomes longer and there is a difference in the distance between the elements. In the case of a switch circuit that turns on all the elements at the same time, a deviation occurs in the current propagation time between the parallel circuit. Since the output waveform from the switch is a superimposed waveform of the output waveform from each circuit, the superimposed waveform will be distorted if there is a deviation in the propagation time. Therefore, we have conceived a radially-symmetrical type switch circuit in which parallel circuits are arranged on a circle so that the distances between elements are equal. With this circuit configuration, waveform distortion due to the propagation distance can be suppressed. We fabricated a modular switch assuming versatility combining SiC power semiconductor and radially-symmetrical circuit structure and evaluated its performance. In the evaluation, two types of circuits, radially-symmetrical type and linesymmetrical type, were fabricated and the waveform distortion of the output voltage was confirmed. CIRCUIT DESIGN Base circuits common to both circuits were designed. By changing the parallel connection structure of the base circuit, radially-symmetrical type and line-symmetrical type are constructed. Only for line-symmetrical type circuits, two kinds of distances between the parallel circuits of 50 mm and 300 mm were prepared so that the dependency of the difference in the distances between the circuits could be confirmed. The number of parallel circuits was set to 8 parallels in all circuits. Furthermore, the output voltage was doubled by stacking the boards in two stages, and the evaluation was carried out in the same way. For SiC semiconductor, SCT 3030 KL made by Rohm was used.

Development of a New Modular Switch Using a Next-Generation Semiconductor

The requirements for a BPM system for the SPring-8 upgrade are long-term stability, sufficient signal intensity and high accuracy*. The design of a button-type electrode for the BPM has been optimized from the perspectives of 1) mechanical structure, 2) rf characteristics, 3) thermal issue. We have adopted the electrode structure without a sleeve enclosing the button to maximize the button diameter for the narrow aperture of the vacuum chamber. The absence of an annular slot around the sleeve in a lodging hole for the electrode eliminates the associated beam impedance. To minimize the beam impedance and the trapped mode heating of the electrode, the rf structure has been optimized by 3D electro-magnetic simulations. To suppress the ohmic loss on the button and center pin thermally isolated from the water cooled BPM block, we have selected molybdenum as a material with high electric and thermal conductivities. The reduction of the heating suppresses thermal deformation of the electrode and the BPM block, and improves thermal stability of the BPM system. The mechanical tolerance of the electrode was defined to fit the error budget for the total BPM offset error of 0.1 mm rms.

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Design Optimization of Button-Type BPM Electrode for the SPring-8 Upgrade

The Compact Energy Recovery Linac (cERL) at KEK is a test accelerator to develop ERL technologies and to operate with a high average beam current and a high beam quality. cERL consists of a photoinjector, a main linac (ML) for energy recovery, a recirculation loop and a beam dump (see Fig. 1). A recent upgrade of the cERL to the middle Infrared Free Electron Laser (IR-FEL) imposed new conditions to maintain beam parameters. Therefore, the injector should be optimized to meet the following requirements at the exit of the main linac. The rms bunch length should be 2 ps, the rms longitudinal emittance should be kept the least, and simultaneously the rms transverse emittance should be kept less than 3 π mm mrad. In this work we describe the strategy and results of the injector optimization to achieve the better performance of the cERL-FEL.

Injector Optimization for the IR-FEL Operation at the Compact ERL at KEK

Ceramics chamber with integrated pulsed magnet (CCiPM) is a new air-core type magnet that has a plan to be used as a multipole injection pulsed magnet, a dipole injection kicker, and a fast correction kicker in the next-generation light source. The magnet coils are implanted completely into the thickness of cylindrical ceramic and integrated with ceramic structurally. The first CCiPM was developed for an internal diameter of 60 mm as a magnet bore to establish the basic production techniques. The technique has been enhanced to realize narrower bore over 4 years, and finally, the achieved internal diameters were 40 and 30 mm in newly developed CCiPM. These super narrow bores have an expectation to conform to the size of the vacuum beam duct in the ring of a future light source.

Newly Development of Ceramics Chamber with Integrated Pulsed Magnet for Super-Narrow Bore in KEK-PF

We are pushing forward the development of a pulsed magnet that has a combined structure of magnet coils with a ceramic vacuum chamber, aiming to realize a small gap. The structure we are developing is that single turn air-coils are implanted along the longitudinal axis in the cylindrical ceramic chamber wall with thickness of 5mm. The ceramic wall works for separating the vacuum from the atmosphere, as well as holding the coil structures mechanically and the electrical insulation of coils. By this structure, magnet pole edges can be set close to the inside diameter of the chamber. The small gap increases magnetic field strength, which is for shorter length, and, as a result, the small magnet size reduces the inductance, which is for shorter pulse. We achieved the continuous operation over 200 days, without any failure, of current-excitation with 20 kV, 7.7 kA pulse with 4-μsec width and repetition of 1 Hz, using the dipole type prototype with a bore radius of 30 mm and magnetic length of 0.3m in 2013, while maintaining the vacuum pressure less than 10⁻⁶ Pa. In this conference, we will discuss about the availability and practical utility with the magnetic field output performance.

Development of the Ceramic Chamber Integrated Pulsed Magnet Fitting for a Narrow Gap

An air-core magnet named Ceramics Chamber with integrated Pulsed Magnet (CCiPM) is being developed at the photon factory (KEK-PF), which will have several applications for the future light source. One prototype has been developed as a dipole kicker whose bore is only 30 mm. Due to the type and structure, it’s expected to have strong magnetic field, fast pulse, and high repetition rate. After finishing the offline measurement of magnetic field and evaluation of vacuum tightness, the CCiPM was installed in the beam transport-dump line of PF to have an online beam performance and durability test. The results of the magnetic field measurement and beam performance test will be reviewed.

Magnetic Field Measurement and Beam Performance Test of Ceramics Chamber with Integrated Pulsed Magnet at KEK-PF

A chicane magnet was newly installed between two undulators of the IR-FEL in the cERL in order to increase the FEL gain and pulse energy by converting the energy modulation to the density modulation in an electron bunch. It consists of three dipole magnets with laminated yokes made of 0.1-mm-thick permalloy sheets and the coil currents of the three magnets are independently controlled by three power supplies with the maximum current of 10 A. The current ratio of the three dipole magnets was tuned after installation to make its orbit bumps closed and then the chicane magnet was used in the FEL operation. We present the specifications and operational performance of the chicane magnet. INTRODUCTION The IR-FEL was constructed in the Compact ERL (cERL) at KEK from October 2019 to May 2020 for the purpose of developing high-power mid-infrared lasers for high-efficiency laser processing utilizing molecular vibrational photo-absorption [1]. The role of the chicane magnet is to increase the FEL gain and pulse energy by converting the energy modulation to the density modulation of an electron bunch (microbunching), shown in Fig. 1. Figure 1: Schematic illustration of the effect of the chicane magnet in an FEL. R56 means the longitudinal dispersion of the chicane magnet. The chicane magnet was installed between the two 3-m FEL undulators [2]. Figure 2 shows layout of the cERL FEL components including the chicane magnet between the undulators. In this paper, we describe specifications, field distribution and bump orbits, tuning of bump orbits and operational performance of the chicane magnet. Figure 2: Layout of cERL components including the chicane magnet between the two FEL undulators. SPECIFICATIONS Figure 3 shows the chicane magnet installed in the cERL. The chicane magnet consists of three dipole magnets BMIS01, 02 and 03. The yoke lengths are 70, 140 and 70 mm for BMIS01, 02 and 03 respectively and the total length of the chicane magnet is 458 mm including the coils. The yoke width and height are 180 and 270 mm and the magnetic gap is 32 mm. The yokes of the chicane magnet are made of 0.1-mm thick laminated permalloy with high permeability and low hysteresis and eddy currents. The turn number of the magnet coil made of a copper wire is 168 and the coil current of each dipole magnet is independently provided by a power supply up to 10 A. The specification of the chicane magnet is showed in Table 1. The chicane magnet was originally produced as the phase shifter prototype of a polarization-controlled undulator and reused for the cERL IR-FEL [3]. Figure 3: Chicane magnet installed in the cERL. ___________________________________________ † noro.nakamura@kek.jp 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-TUPAB064 TUPAB064 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 1512 MC2: Photon Sources and Electron Accelerators A18 Energy Recovery Linacs Table 1: Specifications of the Chicane Magnet Yoke Material 0.1-mm permalloy lamination Permeability 400000 (max.) Saturation field 0.75 T

Specifications and Performance of a Chicane Magnet for the cERL IR-FEL

We advance the development of Ceramics Chamber Integrated Pulsed Magnet (CCIPM) of air-core type as the application to low emittance ring with a narrow bore of light source accelerator in the future. The CCIPM is composed of ceramics cylinder of 60 mm diameter and four copper coils, which are implanted in the groove penetrated on the ceramic thickness along 30 cm length by silver brazing*. In addition to this structure, we succeeded in the implementations of cable connecting base that mechanically connect the coils and power supply with feeder lines and the pattern shape coating inside the ceramic cylinder. Improved brazing technique made it possible to braze the coil and the base on the coil at the same time that the coils are implanted in the ceramic thickness. Newly developed functional coating can reduce the eddy current caused by main magnetic field and pass the alternate component of beam wall current by capacitance structure. We report the details about the performance from the viewpoint of vacuum, magnetic field, insulation on the accelerator implementation with the approach to new technical development, and the preparation progress of beam test in beam-transport line.

Chikaori Mitsuda

Papers

Development of the Ceramic Chamber Integrated Pulsed Magnet Fitting for a Narrow Gap

Newly Development of Ceramics Chamber with Integrated Pulsed Magnet for Super-Narrow Bore in KEK-PF

Magnetic Field Measurement and Beam Performance Test of Ceramics Chamber with Integrated Pulsed Magnet at KEK-PF

Specifications and Performance of a Chicane Magnet for the cERL IR-FEL

Accelerator Implementing Development of Ceramics Chamber with Integrated Pulsed Magnet for Beam Test