Shigeki Sasaki

Construction of insertion devices for elliptically polarized synchrotron radiation

Two new insertion devices for the generation of elliptically polarized synchrotron radiation have been constructed to be installed in two electron storage rings, the Accumulation Ring for the TRISTAN project and the Photon Factory ring at KEK, National Laboratory for High Energy Physics. These new light sources are designed to produce (1) intense radiation with a degree of circular polarization (Pc) between 0.5 and 0.9 in hard x‐ray region, and (2) quasimonochromatic radiation with Pc>0.7 in vacuum ultraviolet region.

Construction of a multiundulator, Revolver No. 19, at the Photon Factory

A multiundulator, Revolver No. 19, was constructed and installed at the straight section (B 18‐B19) of the 2.5‐GeV Photon Factory storage ring. The mechanical structure of Revolver No. 19 consists of a main frame and two rotatable beams with four base plates, on which undulator magnets with four different lengths of period are mounted. A pair of undulator magnets with a desired period length can be selected by revolving the rotatable beams. The energy range of the radiation covered by fundamental peaks from the undulator magnets is from 7.8 to 1150 eV.

Construction of a multipole wiggler, MPW♯13, at the Photon Factory

An insertion device, MPW♯13, which can be operated in both wiggler and undulator modes, is presently under construction at the Photon Factory (PF). When installed in the PF storage ring, this device will produce wiggler radiation in the hard x‐ray region, and also undulator radiation in the vacuum‐ultraviolet (VUV) and soft x‐ray regions. The wiggler structure employs 27 magnetic poles with a period length of 18 cm. The maximum peak field of the device of 1.5 T is attained via the hybrid configuration of its magnetic poles. Calculations of the spectral brilliance of the device exhibits the following features: in the wiggler mode, the brilliance at 10 keV will exceed that of the PF bending magnet radiation by a factor of 30; and in the undulator mode it will be between 10 and 100 times higher, from 10 eV to 1 keV, utilizing up to the fifth harmonic.

Construction and operation of the multipole wiggler, MPW♯16, at the Photon Factory

A high‐field multipole wiggler (MPW♯16), which was composed of hybrid‐configured permanent magnets, was completed and installed in the 2.5‐GeV Photon Factory (PF) storage ring as the third insertion device. Compared to the synchrotron radiation from the bending magnet on the PF ring, the radiation from the MPW♯16 has two orders higher brilliance in the x‐ray region and three orders higher in the vacuum ultraviolet region. The stable operation of the storage ring coupled with the MPW♯16 has been confirmed through various machine studies.

Upgrade of BPM Electronics for the SPring‐8 Storage Ring

SPring‐8, a 3rd generation synchrotron light source, has operated since 1997. Improvement of BPM performance is required as a part of upgrading activities of the storage ring as a light source. We have developed new electronics circuits for signal processing of the storage ring BPM, with target performance of sub‐μm range resolution with sufficiently fast measurement speed and good long‐term stability. A set of the new circuits consists of multiplexers, an RF amplifier, a mixer, an IF amplifier, and a local oscillator for analog signal processing. The IF amplifier outputs are sampled with 16‐bit 2‐MSPS ADC on ADC boards and the data are sent to a DSP board. The sampled data are processed and converted to position information in the DSP. A multiplexing method was employed to have a better stability of the performance by cancellation of variation common to each channel. Evaluation of the performance by using a prototype shows that position resolution well into the sub‐μm range has been achieved with a bandw...

Development of Beam Diagnostic System for the SPring-8 Upgrade

For the upgrade of SPring-8, the design and development of the beam diagnostic system are in progress. The pointing stability of the photon beam is essentially important. The demands for the position and angular stabilities of the source electron beam are less than 0.5 μm and 0.2 μrad, respectively. To fulfill the stringent demands, both an electron beam position monitor (BPM) and an x-ray photon beam position monitor (XBPM) with sufficient accuracies, resolutions and stabilities are necessary. We are developing a high-resolution button-type BPM system having enough long-term stability. For stable user operation, precision diagnostics of beam current, beam size, etc. and control of collective beam instabilities are also crucial. The diagnostic instruments other than the BPM and the XBPM have been already implemented at the present SPring-8 storage ring with sufficient performances for the upgraded ring.

Solid-state Compact Kicker Pulsar using Strip-line Type Blumlein with SIC-MOSFET in Spring-8

In the case of handling an electron beam by bunch-bybunch and turn-by-turn with a kicker at the SPring-8, the performances required to a pulsar are short pulse width (<40 ns) and high repetitions (208 kHz). For this purpose, we developed the prototype Blumlein pulsar as an experimental attempt. The prototype was composed of the solid state switch of SiC power MOSFET and 6 series Blumlein pulse forming networks (BPFNs) made by stripline of 2 m. By connecting the pulsar to coil inductance of 2.5 μH, the 2.0 MW power pulse of 158 ns pulse width was obtained without any failure by supplying 2 kV high voltage. At 120 pps burst repetitions under natural air-cooling condition, the high current stability of 0.14 % and high amplified voltage of 14.0 kV was achieved. INTRODUCTION SPring-8 storage ring has no enough space to install the additional kicker system due to the many non-linear optics correction magnets. The averaged remaining drift space is about less than 30 cm length. There are two subjects in our kicker pulsar development. Firstly, pulsar must satisfy requirements of both compact size and high power output to compensate the shortness of the magnet length to install small space anywhere. Secondary, pulsar must be able to generate a pulse with high repetition and short pulse width when it is used as beam control of turn-by-turn and bunchby-bunch. For first requirements, our kicker system is separated into magnet coil, pulsar(=driving circuit), and DC high voltage and control power source. By separating the kicker system into three functions, separated compact pulsar can be set up near to the load so that the lead-line inductance from the pulsar to a magnet is reduced as small as possible. In our system, the compactness of the pulsar is one of the important feature. One of the solution realizing the second requirements is using solid-state power MOSFET instead of the thylatron, because power MOSFET prepares merits of low switching power loss, fast switching speed and small discrete package. But, in order to increase the voltage resistance of the pulsar, the highly technological development to stack the serial and parallel jointed MOSFET is needed so that the disadvantage of its small breakdown voltage is compensated. In the SPring-8, compact pulsar using Si MOSFET is operated in the storage ring for fast correction kicker [1]. ∗ mitsuda@spring8.or.jp This pulsar is composed of single switching module which use 2 serial (2s) and 6 parallel (6p) jointed Si MOSFETs whose breakdown voltage is 1.2 kV each [2]. Therefore, this module has the withstanding voltage of 2.4 kV. To increase output voltage of the pulsar and to achieve a shorter pulse by using this switching module, Blumlein amplifying method is proposed. Because Blumlein length is in proportion to the generated short pulse width, it is suitable to make a pulsar compact for short pulse generation. As a result, an amplified high power output, short pulse and compactness which are our development purposes are accomplished by Blumlein circuit with MOSFET switch. PROTOTYPE BLUMLEIN CIRCUITS SiC Solid-state Switcher Initial targeted values of output pulse width, high voltage, current and burst repetition rate were 100 ns, 12 kV, 200 A and 1 kHz respectively for an inductance load. In order to realize these parameters, 6 series BPFNs was designed to amplify the supplied 2.0 kV high voltage by a factor of 6. In this development, our already developed 2.4 kV switching module was modified for two technical elements. First one is that SiC power MOSFET (Rohm:SCH2080KE) which has smaller ON resistance and faster switching speed was introduced to our switching module instead of Si power MOSFET (IXYS:IXFB30N120P) for the first time. The gate driver circuit was also improved to fit to the SiC gate characteristics. Second one is that MOSFET arrangement on the board of Figure 1: Schematic view of n series BPFNs circuit. our module was changed. Whereas 2s x 6p jointed MOSFET were arranged in round circle shape to reduce the stray impedance to output terminal in utilization as single module, 1s x 6p jointed MOSFET were re-arranged in arc shape to the BPFN terminal. By this way, the impedance from 6 parallel MOSFETs on the single module to single line of BPFN was Proceedings of IPAC2016, Busan, Korea THPMW020 07 Accelerator Technology T16 Pulsed Power Technology ISBN 978-3-95450-147-2 3585 C op yr ig ht

Long-Term Stability of the Beam Position Monitors at SPring-8

Stability of the BPM system is critical for synchrotron light source rings to keep the quality of photon beams and to stabilize the photon beam axes. The BPM system of SPring-8 has suffered from fluctuating gain imbalances among 4 electrode channels, which results in variations of offsets for beam position measurement. We recently surveyed the logged data of the BPM and the operating environment, and revealed several features of variations of the offset errors of the BPM. To cure step variations of the offsets, inspections of switch modules of the readout circuit are necessary. For variations correlated with the dew point of the environment, we consider that a possible cause is change of reflection coefficients in the BPM cables damaged by radiation. Further investigations are necessary to find the causes of other variations of the BPM offset errors.

Magnetic-field Variable Permanent Dipole Magnet for Future Light Sources

A permanent dipole magnet with variable magnetic field has been designed, fabricated, and tested at SPring-8. Permanent magnet can be advantageous over electromagnet in terms of power consumption, stability and reliability etc. One of critical issues to apply permanent magnets to future light sources and other accelerators is that the magnetic field should be somehow tuned. In designing future light sources, combined-function or longitudinal gradient magnet may play a key role in achieving extremely small emittance. Therefore, it may not be appropriate to change a gap for changing the field. We have proposed an alternative way to tune the magnetic field of permanent magnet by using outer plates, and the performance has been investigated.

High‐speed and simultaneous photon beam diagnostic system using optical cables at SPring‐8

We have developed a high‐speed and simultaneous photon beam diagnostic system using optical cables at SPring‐8. The system is composed of blade type X‐ray beam position monitors (XBPM) in front ends, optical cables spread over the experimental hall and multi A/D converters at the photon beam diagnostic station. Analog data of the beam positions are transferred through the optical cables. The multi A/D converter allows us to browse and process the data from the main control room in real time. The features of the system are the wide band‐width, the ability of full‐time observation with XBPMs and the compatibility to the monitoring system of electron beam position monitors in the storage ring. The system has been routinely used for high‐speed and simultaneous measurements of photon beam and electron beam.