Acceleration of high-energy electrons traveling at high speed generates radiation. In particular electron forced to move in a circular orbit undergo centripetal acceleration and emit strong radiation in a direction tangential to the orbit in a bending magnet (Fig. 1). This is known as synchrotron radiation. With SPring-8 (electron energy: 8 GeV), white synchrotron radiation can be obtained over a broad range of wavelengths, from the far infrared through vacuum ultraviolet, soft x-rays, and x-rays, to gamma rays.
Insertion devices such as undulators (Fig. 2) and wigglers, composed of permanent magnets with alternating polarity, cause electrons to travel in a sinusoidal orbit. All synchrotron radiation is generated as every turn in the orbit overlaps with the direction of travel, thereby causing the emission of synchrotron radiation of higher brilliance. With undulators in particular, the overlapping waves of synchrotron radiation interfere with each other, thereby generating monochromatic synchrotron radiation of higher brilliance at a specific wavelength.