SOME DESIGN CONSIDERATIONS FOR THE ESRF UPGRADE PROGRAM EXPERIMENTAL

In 2008, the Council of the European Synchrotron Radiation Facility (ESRF) launched the ESRF Upgrade Programme 2009-2018, an ambitious ten-year project serving a community of more than 10,000 scientists. Funding for the first phase of the Upgrade (from 2009 to 2015) has been secured to deliver: • eight new beamlines with capabilities unique in the world; • refurbishment of many existing beamlines to maintain them at world-class level; • continued world leadership for X-ray beam availability, stability and brilliance; and, • major new developments in synchrotron radiation instrumentation. One of the key elements of the Upgrade Program is to produce nano-sized beams. This will require the construction 120 m and in some cases even 250 m long beamlines. A combination of extended experimental hall and satellite buildings will address this need. One particularly important issue is the design of the concrete slab that will host these new beamlines. The vibrational stability of the experimental hall slab is a key aspect to in the slab design. However, recent hydrostatic levelling system (HLS THE ESRF UPGRADE PROGRAM ) measurements indicate that slab bending movements driven by temperature gradient variations through the slab could also be a very important consideration in beamline stability and performance. This paper presents the measurements that have led to this conclusion. X-rays are ideally suited for studying matter at the atomic lengthand time-scales. Scientists use brilliant beams of X-ray photons for experiments in physics, chemistry, health and life sciences, material sciences, environment, industrial research and increasingly cultural heritage. Demand for high-brilliance X-ray beams is continually growing, with user communities requiring ever increasing levels of performance along with ease of access to and use of the light sources. At the ESRF, the user communities are specifically demanding smaller nanosized beams with higher brilliance, improved facilities on the beamlines and not least more beam time. The ESRF Upgrade Programme is serving this demand with the additional objective to maintain the ESRF's role as the leading European provider of hard X-ray light. The * An HLS is a tool that is used to precisely monitor vertical motion in sensitive applications. Upgrade focuses on five core areas of applied and fundamental research: • nanoscience and nanotechnology, • pump-probe experiments and time-resolved diffraction, • science at extreme conditions, • structural and functional biology and soft matter • X-ray imaging. Producing nano-sized beams needs long beamlines, which at the ESRF will reach 120 metres and in some cases even 250 metres. A combination of extended experimental hall buildings along with satellite buildings for very long beamlines will address this need. Particular care and effort is being put into the design of the concrete slab to host new beamlines as its stability is pivotal to the beamlines meeting their design performance. ESRF EX2 SLAB, LONG BEAMLINES AND TOLERANCES The ESRF upgrade program calls the construction of a number of long beamlines (upgrade program beam lines UPBLs) in several thousand square metres (nominally 6000 m) of new experimental hall (EX2) floor space. The key issue for this new experimental hall slab is its stability. Stability plays a vital role in the performance of the UPBLs because the majority of them will be involved in nanometre scale science. A simple schematic drawing with the key elements of a typical nano-focus beamline is shown in Figure 1. Figure 1 Schematic of a typical nano-focus beamline. Long beamlines can be compared to a microscope whose primary measure of merit is spatial resolution. The size of the incident X-ray spot – or probe on the experimental specimen determines this resolution. One of the principal aims of long beamline experiments is to focus the X-ray beam to the smallest possible probe size. When using a single focusing element, which is the case with long beamlines, the size of the focal spot (probe) is † http://www.esrf. fr/AboutUs/Upgrade limited by the demagnification of the source size and by the diffraction limit (see Figure 2). Figure 2 The size of the focused X-ray probe spot size depends on: the source size, the distance between the source and the focusing optics p, and the working distance between optics and the experimental sample q. At the ESRF p is nominally 150 m and q is in the order of 0.05 m. The demagnification is therefore q/p=3000 giving a theoretical probe size of 10 nm. Actual probe size is expected to be between 20 and 50 nm. In theory a small beam could be produced using a more complicated optical arrangement on a shorter beamline. In practice, however, the number of X-ray optical components should be restrained whenever possible to minimise beam degradation from sources such as mirror slope errors, absorption in refractive elements, and thermal and vibrational stability. Expected long beamline probe sizes will range between 20 and 50 nm. [1] Figure 3 Uncertainty due to translation and rotation errors. Considering the X-ray probe spot size is approximately 50 nm and an acceptable spot drift δ is 10% of its size, or 5 nm, the effect of a pure translation is given by: 5 nm 3000