Recent Progress in X-ray Emittance Diagnostics at Spring-8

At the SPring-8 storage ring, we have recently developed two X-ray instruments for emittance diagnostics. The one for a bending magnet source is the X-ray pinhole camera which directly images the beam profile. A pinhole in the atmosphere is composed of combined narrow X-Y slits made of tungsten. A scintillator crystal is used to convert the X-ray beam image to a visible image. The spatial resolution is about 7 m. It is operated for continuous emittance diagnostics and coupling correction of user operation of SPring-8. The other for an undulator source is the X-ray Fresnel diffractometry monitor. Monochromatic X-rays are cut out by a single slit, and the vertical beam size is deduced from the depth of the central dip in a double-lobed diffraction pattern. Resolving beam size less than 5 m is feasible. INTRODCUTION Light source rings are competing to achieve lower emittance and emittance coupling ratio for higher brilliance. Serious and elaborate efforts are being paid for upgrade plans of existing synchrotron radiation (SR) rings or new plans of low emittance rings. X-ray SR is the key diagnostics probe for nondestructive beam emittance [1]. Both direct imaging and interferometric techniques can resolve the micrometerorder transverse beam size. The beam emittance is obtained from the measured beam size with the knowledge of the betatron and dispersion functions and the beam energy spread. At the SPring-8 storage ring, we have recently developed two X-ray instruments for emittance diagnostics. The one for a bending magnet source is the X-ray pinhole camera which directly images the beam profile. The spatial resolution is about 7 m. It is operated for continuous emittance diagnostics and coupling correction of user operation of SPring-8. The other for an undulator source is the X-ray Fresnel diffractometry (XFD) monitor [2,3]. Monochromatic X-rays are cut out by a single slit, and the vertical beam size is deduced from the depth of the central dip in a double-lobed diffraction pattern. Resolving beam size less than 5 m is feasible. X-RAY PINHOLE CAMERA The layout of the SPring-8 X-ray pinhole camera is shown in Fig. 1 and the specifications are summarized in Table 1. The source point is in a dipole magnet (29B2), 1.0 mrad inside from the edge. The magnetic field and the critical photon energy of emitted X-rays is 0.5 T and 21.1 keV, respectively. The X-ray window is located at a distance of 6.2 m from the source point. The window material is aluminium alloy of 3 mm thickness. The window separates the ultra-high vacuum and the atmosphere, and the X-rays emitted in the source dipole magnet go out to the atmosphere. The pinhole assembly in the atmosphere is located at a distance of 11.4 m from the source. It is composed of Figure 1: Layout of the X-ray pinhole camera of SPring-8. ___________________________________________ *[email protected] Proceedings of IBIC2015, Melbourne, Australia TUCLA02 Transverse Profile Monitors ISBN 978-3-95450-176-2 283 C op yr ig ht © 20 15 C C -B Y3. 0 an d by th e re sp ec tiv e au th or s Table 1: Specifications of the SPring-8 X-ray Pinhole Camera Light Source Bending Magnent (29B2) Pinhole Distance from Source (m) 11.4 Aperture Size (m) 20 x 20 Scintillator Distance from Source (m) 34.3