Ultra-short electron bunch length measurement was demonstrated with a dual-band Michelson interferometer observing coherent transition radiation (CTR). Simultaneous detection of CTR with two different infrared detectors with different bands enabled precise determination of the bunch length. The methodology analysis of the obtained interferograms was also examined with a model-based analysis. The capability of electron bunch lengths for the present measurement system was evaluated to be 3–100 fs with non-precise measurement region of 15–30 fs. Experimental frequency spectra of CTR were also reconstructed under assumption a Gauss-distribution electron bunch and gave good agreement with a Gaussian bunch form factor. Detailed analysis of obtained interferograms revealed simultaneous dual-band detection is important to examine obtained value of bunch lengths.
Accelerator-based THz radiation has been expected to realize a high power broad-band source. With a low emittance and short-bunch electron beam at a high repetition rate, a scheme of coherent-diffraction-radiation in an optical cavity layout is proposed. It can greatly enhance the efficiency of the radiation by the stimulated radiation process between bunches. We give an introduction of the principle of this process. We performed an experiment at cERL in KEK. A sharp resonance signal of THz which indicates broad-band stimulated radiation correlating with beam deceleration was observed while scanning the round-trip length of the cavity. It proves the efficient beam-to-radiation energy conversion due to the stimulated radiation process.
GaAs/GaAsP strain-compensated superlattices (SLs) were developed for spin-polarized electron sources. The strain-compensated SLs effectively prevented strain relaxation and showed excellent crystal quality compared to the conventional strained SLs. 24-pair of GaAs/GaAsP strain-compensated SL photocathode exhibited a maximum spin-polarization of 92% with a high quantum efficiency of 1.6%. 1.6% is over 3 times higher than those of the strained SLs. A simulation based on the diffusion model proved that further improvement of the quantum efficiency was possible in the thicker stain-compensated SLs.
At the XFEL facility SACLA, a beam switching system composed of a pulsed kicker magnet and a DC septum magnet had been installed to perform pulse-by-pulse XFEL switching operation between two XFEL beamlines (BL2 and BL3). However, CSR effects at a 3 degree dogleg beam transport to BL2 severely limited the peak current of an electron beam. In order to cancel out the CSR effects, new beam optics, which is symmetric in terms of the deflecting field distribution, is introduced to the dogleg. Here, the deflecting angle of a new kicker magnet working as the first bending magnet in the dogleg is increased from 0.5 to 1.5 degrees. To drive the new kicker magnet, a high-power pattern power supply, whose maximum output power is 0.3 MW (299 A and 1 kV), has been developed using SiC MOSFETs as switching elements. This power supply can generate bipolar trapezoidal current waveforms at 60 Hz with a current stability of 20 ppm (peak-to-peak), and the amplitude and polarity of each waveform are controllable from pulse to pulse depending on beam energies and destinations. By using the new beam switching system, we have succeeded in the multi-beamline XFEL operation with high peak current electron beams, which almost doubles the time slots for user experiments.
Application of ion accelerator is one of important innovation for the society of radiology and radiation oncology. Electron linear accelerator has been utilized mainly for such application long time and became familiar to many hospitals. Sumitomo Heavy Industries, Ltd. (SHI) started manufacturing of accelerator from 1972 for Osaka University, Tohoku University, RIKEN separated sector cyclotron and so on. SHI also started manufacturing medical small cyclotron for PET tracer system in 1980. As for the cancer treatment application, SHI provided the first proton therapy system for National Cancer Center in Japan. The history of the developments and current activity is introduced.
I review the history of the Nichicon’s power supply for accelerators and I show the specifications and experimental data on the Klystron power supply of TRISTAN main ring, the injection bump magnet power supply of SPring-8, and the beam distribution kicker magnet power supply of SACLA which I was involved in. Along with the high performance of the accelerators, higher precision of its power supply has come to be required. We will work on the development of SiC modules, etc., to realize a faster and more accurate power supply for the future in order to contribute to the development of the accelerators.
The committee of Science Council of Japan to evaluate ILC (International Linear Collider) project published the report on 19 Dec. 2018. Although the committee recognized the scientific value of ILC, the Science Council of Japan would not recommend the unconditional approval of ILC project, because there are many issues to be solved. Japanese government will decide their policy for ILC on March 2019. Depending on the policy, an effective approval of ILC project is expected. ILC is now in a transition phase from the un-official preparation to the official project. The ILC summer camp has been held since 2010 every year for intense discussion among theoretical physicists, experimental physicists, and accelerator physicists. By the start of the official project, the role of the summer camp to develop a relationship of mutual trust among them, will be terminated. The ILC summer camp should be reformed as “Neo ILC summer camp” with a new role in the ILC project organization. In this article, I report the last ILC summer camp by touching the latest situations of ILC project.
The 1st International School on Beam dynamics and Accelerator technology (ISBA18) was held in Hiroshima International Plaza at Higashihiroshima, Hiroshima from 26 to 30 Nov., 2018. This school was organized giving an opportunity to learn the beam dynamics and accelerator technologies as foundations of the accelerator for Asia students and young researchers. It could be a gateway to start the real study on accelerator development for those people. In this article, we report the school and consider the education and training for young people in the 21st century.