“The philosophy of the SLS has always been to explore novel techniques and use cutting-edge hardware, which has resulted in breakthroughs in areas such as imaging, X-ray spectroscopies, macro-molecular crystallography and detector technologies,” write Phil Willmott and Hans Braun in an article about the SLS 2.0 upgrade in Synchrotron Radiation News this month.
This philosophy of innovation underpins the comprehensive upgrade of the storage ring and X-ray sources of the Swiss Light Source SLS, which is currently underway.
Better behaved electrons mean brighter X-ray light
The storage ring is the part of the facility where electrons zip around close to the speed of light, generating X-ray light as they go round the bends. The main parameter used to describe the quality of the X-ray light produced is brilliance, which effectively indicates how bright, compact, and well collimated the light is.
For a more mathematical definition, brilliance is defined as the photon flux divided by the emittance – a parameter that describes how collimated the electron beam is and its cross-section in the storage ring. To maximise brilliance, the electron emittance should be as low as possible.
This is the principle of a diffraction limited storage ring (DLSR): reducing electron emittance to the point that it is as small or smaller than that of the X-ray photons. The emittance of the X-ray photons is governed by fundamental diffraction phenomena. The performance of the synchrotron is thus limited by diffraction and no longer by the properties of the electron beam.
The primary way in which this is achieved for SLS 2.0 is with an innovative arrangement of magnets for bending and focusing the electrons. By using more, smaller magnets, these smooth out the curves of the electrons round the storage ring, while keeping them close together.
The new SLS 2.0 storage ring will allow the electron emittance to drop by a factor of thirty-five. With innovative new undulators enabling additional so-called radiation damping, the drop in electron emittance should exceed a factor of forty.
Read more on PSI website
Image: Work to install the new storage ring is already underway at the SLS. (Image: Paul Scherrer Institute
Credit: Markus Fischer