Laser wakefield acceleration has been well recognized as a compact advanced acceleration regime with extremely high acceleration gradient. For the application concerns, the temporal information of the electron bunches from laser wakefield acceleration is of great importance. For single shot monitoring of such a parameter, we introduced the electro-optic spatial decoding technique to the research of laser wakefield acceleration. Interesting phenomena were observed when detecting the Coulomb field of the electron bunch at a position very close to the plasma source. The relative timings of electron bunches were detected for various plasma densities and physics behind were investigated. Temporal multi-bunch structures were observed. The smearing process of the electro-optic spatial decoding was detailly discussed. Our research demonstrated the capability of electro-optic sampling technique as a single-shot electron temporal monitor for laser plasma acceleration studies.

SuperKEKB is an asymmetric-energy electron positron collider based on the “nano-beam scheme,” where two low emittance beams collide with a large crossing angle at the interaction point (IP). Chromatic x-y coupling at the IP needs to be corrected to realize such low emittance beams and recover luminosity. The chromatic x-y coupling correction can be done using skew sextupole magnets, as was done at KEKB B-factory in 2009. SuperKEKB adopted correction by skew sextupole field generated by changing the roll angles of the sextupole magnets, instead of adding skew sextupole magnets and power supplies. In December 2021, one of the chromatic x-y coupling parameters was varied using different setups of the rolling angles of the 24 sextupole magnets for the first time in a collider. It was found that the vertical emittance growth at the primary and secondary synchro-beta resonance lines can be controlled by rolling the sextupole magnets. Luminosity increase followed after optimizing the chromatic x-y coupling parameter and finding a better tune working point. The tilting system is described, and the study results are summarized in the report.

To demonstrate the operation of a mid-infrared SASE FEL system in an energy recovery linac (ERL) layout, we constructed an SASE FEL setup in cERL, a test facility of the superconducting linac at KEK. Despite the adverse circumstance due to the given boundary condition of the facility and the limited budget and time schedule of the project, we successfully established the beam condition at the undulators, and observed FEL emission at a wavelength of 20 µm. We present the background stories that we have experienced in the project.