NEW APPARATUS, UPGRADES & METHODOLOGY 149 A high-flux undulator beamline for high-resolution inelastic X-ray scattering Non-resonant, high-resolution, hard-X-ray, inelastic scattering is, in principle , a nearly ideal tool for the condensed matter scientist. The technique directly probes the electronic density-density correlation function, the dynamic structure factor, S( Q , ω ), over correlation lengths comparable to unit cell sizes, with resolution that can be at the meV level. These scales are interesting as they are the energy scales of phonons, and low-lying electronic excitations, and also because it is the interplay between low-energy excitations that governs the behavior of many of the most interesting and technologically relevant materials. When one also notes that the brilliance of a third generation synchrotron radiation source allows micron-scale beam sizes to be achieved, one has, again in principle, a very powerful probe of the dynamical behavior of condensed matter systems. The above optimistic picture, however, lasts only until the count-rate limitations of real experiments are encountered. While modern synchrotron radiation sources provide huge fluxes (~10 13 or even ~10 14 hard X-ray photons/s after a typical monochromator), the first thing an IXS experiment does is reduce this flux by several orders of magnitude to achieve the necessary resolution. Thus, while straining to take full advantage of modern third-generation sources, the final flux on the sample in a high-resolution IXS experiment is more characteristic of a first generation source, and the experiments are correspondingly limited. A survey of published data will show that Optics Hutch MR Optics MR Spect. High Resolution Spectrometer 5m Medium Resolution Spectrometer High Resolution Spectrometer for Electronic Excitations for Atomic Dynamics and Electronic Excitations Backscattering Mono M1 M2 Harmonic Rejection LN2 Cooled Mirror Si (111) Mono LN2 Cooled ~1.8 kW ~200 eV ~0.6mm × 2.6mm Power: <500W ~3 eV ~0.5 W 2 × 1600 kg 1000 kg 2000 kg 500 kg 500 kg 500 kg MR Mono MR Analyzer Array Focussing Mirror Array Detector Sample 42-Element Analyzer Array Detector Array Sample Beam Size: ~0.03mm M3 Focussing Mirror Bent Cylinder 0.001 eV ~0.3 eV ~0.05 W Offset Crystals Backscattering Monochromator Si (nnn) n = 8 to 13 M4 <0.9 25.7 1.4 2.8 6.0 40 10-100 >0.3 >0.3 21.7 17.8 15.8 15.8 15.8 14.4 1.2 1.0 0.8 0.7 0.7 3.4 4.9 4.1 3.4 3.0 10 >10 >10 12 10 8.3 7.4 7.4 16 15 140 230 390 440 440 440 430 Si(13 13 13) Si(11 11 11) Si(8 8 8) Si(8 8 8) Si(8 8 8) Si(8 8 8) 57 Fe Nuclear Resolution (meV) X-ray Energy (keV) Δ Q max (nm -1 ) Q max (nm -1 ) E max (eV) Analyzer Source Flux (GHz/meV) Energy (keV) 16 18 20 22 24 BL43LXU 15m BL43LXU 5m Flux Standard ID Flux (10 14 /s/0.1% BW) 80 40 0 BL43LXU: RIKEN Quantum NanoDynamics (RQD) Beamline for High-Resolution Non-Resonant Inelastic X-Ray Scattering Fig. 1. BL43LXU layout. 150 essentially all work to date using non-resonant IXS with better than ~100 meV resolution, investigates only the very strongest excitations, phonons, and, even then, experiments are often count-rate limited. On this basis, discussions began some years ago about creating a very intense beamline for high resolution IXS. The essential idea was to take advantage of SPring-8’s strengths – the 8 GeV electron energy, in-vacuum undulator technology and the availability of long straight sections – to make a uniquely powerful beamline, with extremely high flux on the sample. This beamline, the RIKEN Quantum NanoDynamics (RQD) beamline was funded by MEXT, through RIKEN beginning in 2009. In October of 2011, RIKEN allocated funds to largely complete it. The target of the beamline is the investigation of dynamics with ~1 to ~100 meV energy resolution, with particular emphasis on high-resolution measurement of electronic excitations, and, then, studies of atomic dynamics of difficult systems. The beamline (see the Fig. 1) is expected to provide about 1 order of magnitude more flux onto the sample than a standard ID and will increase parallelization of data collection by about a factor of 3. It will operate at energies between 15 and 25 keV, with resolutions between 1 and 100 meV. A new design for the medium- resolution spectrometer will allow ~ 20 meV resolution with while a collecting large solid angle and with comfortable space for sample environment. The RQD is now in the first stages of commissioning. The initial 1/3 of the insertion device has been installed, and, at the end of 2011, the mechanics for the first, high resolution, spectrometer was installed. Commissioning is expected to extend into the spring, with first experiments taking place in the summer. Thanks to the additional funding from RIKEN, the completion of the insertion device is planned for early in 2013. Commissioning of the medium resolution spectrometer will begin late in 2012. The initial targets for the beamline are, the extension of high-resolution studies into the field of electronic excitations, for example, to investigate the excite states of orbital order, and several problems in atomic dynamics, including phonons in high- temperature superconductors. Additional details can be found at: http://user.spring8.or.jp/sp8info/?p=3138 Alfred Q. R. Baron SPring-8/RIKEN • JASRI E-mail: baron@spring8.or.jp
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