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Abstract: Accurate electron density mapping is quite a common practice for crystals cooled at low temperature and accurately measured. This is not true for species under external perturbation, due to complicated experimental conditions. Studying molecular crystals in excitedstates is a challenge, Coppens(2009), and a purely experimental electron density mapping is not possible at present. So far, the samelimitation affected molecular crystals at high pressure, with only few attempts to use theoretical multipoles to fit experimental data,Fabbiani (2011). Here we report on the first unconstrained multipolar model, refined for syn-l,6;8,13 biscarbonyl[14]annulene (BCA) at P=7.7 GPa. BCA was the subject of a low temperature data collection by Destro (1995). The molecule (close to C2v symmetry) has afair aromaticity, but it progressively localizes double and single bonds as a function of pressure. At 7.7 GPa the geometrical distortionis quite evident and mirrored by the electron density. The experiment, carried out at Diamond Light Source, was possible combining:a) high energy (40 Kev) to overcome the resolution problems caused by diamond anvil cells and reduce absorption and extinction; b)microfocused beam (30 micron) to minimize spurious X-ray diffusion; c) two crystals in the DAC, to increase data coverage; d)sufficient pressure to quench atomic motion. The final agreement is obviously worse than what typically obtained at ambientpressure. However, the model is satisfactory because: a) the deformation density is sensible and in agreement with the calculated one; b) the distribution of residuals is normal and no significant error is evident. The study proves that aromatic molecules are morereactive when squeezed, in keeping with the recent theoretical study by Hoffmann et al. on benzene. The Figure shows the staticdeformation density of BCA in 3D, obtained from a multipolar model refined against the experimental structure factors.

Open Access

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Abstract: The rate at which X-ray structures of membrane proteins are solved is on a par with that of soluble proteins in the late 1970s. There are still many obstacles facing the membrane protein structural community. Recently, there have been several technical achievements in the field that have started to dramatically accelerate structural studies. Here, we summarize these so-called ‘tricks-of-the-trade’ and include case studies of several mammalian transporters.

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Abstract: The Diamond storage ring uses CESR type superconducting cavities. These cavities have a fixed coupling resulting in fixed Qext which is considerably higher than the optimum. We use 3 stub tuners to match the cavities under these non-optimum conditions. Diamond Cavity-1 will soon be refurbished. This opportunity could be used to lower the Qext on the cavity. One of the options is to modify the coupling tongue geometry along with a matching section. This may require cutting off the beam tube with the coupler for rework or it may need to be newly fabricated. We investigated another option to lower the Qext of the cavity by optimising the location of the window with respect to the cavity, maintaining the same coupling tongue geometry. The height of the waveguide on the vacuum side of the window differs from that of the coupling waveguide on the cavity resulting in a step. The location of window with respect to the cavity makes a significant difference to the ultimate Qext obtained after putting the window in place. In this paper we present the results of our numerical simulations comparing the present and the proposed window position under different operating conditions.

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Abstract: The increasing efforts in the synchrotron light sources community toward the design of a diffraction limited source at multi-keV photon energy have eventually stimulated the existing facilities to investigate possible upgrade paths to higher photon brightness and lower emittances to maintain their competitiveness within the users’ community. We present a possible option for upgrading 3rd generation light sources based on a rebiuld of the arcs with MBA cells, using diamond as an example. Emphasis is given to the AP desing issues with a view to minimal changes to the machine layout, contained cost and minimal downtime

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Abstract: Ultra-low emittance lattices will operate with reduced dynamics apertures. New injection schemes are currently investigated in order to guarantee sufficient injection efficiency. A promising candidate is a pulsed kicker with a nonlinear magnetic field. The studies presented in this paper prove that this kicker allows injection with reduced dynamic aperture and provide minimal perturbation of the stored beam during Top-Up injection. Plans to install such a device at the Diamond light source are outlined.