Observation of grating diffraction radiation at the KEK LUCX facility

The development of linac–based narrow–band THz sources with sub–picosecond, ?J-level radiation pulses is in demand from the scientific community. Intrinsically monochromatic emitters such as coherent Smith–Purcell radiation sources appear as natural candidates. However, the lack of broad spectral tunability continues to stimulate active research in this field. We hereby present the first experimental investigation of coherent grating diffraction radiation (GDR), for which comparable radiation intensity with central frequency fine–tuning in a much wider spectral range has been confirmed. Additionally, the approach allows for bandwidth selection at the same central frequency. The experimental validation of performance included the basic spectral, spatial and polarization properties. The discussion of the comparison between GDR intensity and other coherent radiation sources is also presented. These results further strengthen the foundation for the design of a tabletop wide–range tunable quasi–monochromatic or multi–colour radiation source in the GHz–THz frequency range

Micron-scale laser-wire scanner for the KEK Accelerator Test Facility extraction line

A laser-wire transverse electron beam size measurement system has been constructed and operated at the Accelerator Test Facility (ATF) extraction line at KEK. The construction of the system is described in detail along with the environment of the ATF related to the laser wire. A special set of electron beam optics was developed to generate an approximately 1 mu m vertical focus at the laser-wire location. The results of our operation at the ATF extraction line are presented, where a minimum rms electron beam size of 4: 8 +/- 0: 3 mu m was measured, and smaller electron beam sizes can be measured by developing the method further. The beam size at the laser-wire location was changed using quadrupoles and the resulting electron beam size measured, and vertical emittance extracted