Mitsuhiro Masaki

Two-dimensional visible synchrotron light interferometry for transverse beam-profile measurement at the SPring-8 storage ring.

A two-dimensional visible synchrotron light interferometer has been developed to measure the transverse profile of an electron beam at the SPring-8 storage ring. The new interferometer enables the simultaneous measurement of beam sizes along the major and minor axes and the beam-tilt angle of an assumed elliptical Gaussian distribution. The principle of the interferometer is explained through basic formulae. To calibrate the point-spread function of the interferometer, a simple error model was assumed for disturbances in the amplitude and phase of the light; these disturbances were presumably caused by optical elements, such as mirrors and lenses. The experimental method to determine the parameters in the error model is shown. To verify the two-dimensional profiling capabilities of the interferometer, an electron beam stored in the SPring-8 storage ring operated at various working points was observed. A beam broadening from 20 to 120 microm in the vertical direction and changes in the beam-tilt angle were clearly observed at working points close to the differential resonance. However, the vertical spatial resolution is limited by the available vertical separation of the apertures of the diffracting mask because of the narrow aperture of the upstream vacuum duct.

Characterizations and Applications of the Insertion Device of the SPring‐8 Diagnostics Beamline II

An insertion device (ID05) of the SPring‐8 diagnostics beamline II (BL05SS) was characterized from the aspects of both the magnetic field performance and the spectral performance as a high K wiggler, which was confirmed to have the field performance with the rms phase error less than 2 degree. Meanwhile, the spectral performance of ID05 as an undulator with small K was also investigated by the energy spectrum measurements. The rms phase error less than 2degree leads us to apply the wiggler radiation on the higher harmonics to the beam diagnostics. We successfully demonstrated an application to the energy‐spread diagnostics of electron beam using the 19th harmonics.

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.

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.