My abstract for this talk published by the ACA in its Abstracts book was:- When ESRP released its X-ray undulators specifications in the1980s the intensities were unprecedented. A report was prepared for ESRP, at CERN, based on detailed analyses in a visit I made to LURE to work with Roger Fourme, We modelled cryomounting of a protein crystal with a Cu stalk to carry away heat from the sample absorbed from the X-ray undulator beam & modelled thermal heating at short wavelengths. The reduced diffraction efficiency of the sample could be handled by the increased brilliance. The ESRP was already 5GeV and so also a high photon energy source. Considering the ratio of the diffraction efficiency and the absorbed photon versus energy led Uli Arndt to the idea that gains in measurable diffraction data per protein sample were possible. At the SRS wiggler, with Britt Hedman and Keith Hodgson, an experimental simulation of the undulator intensity at an ESRF but with white beam radiation showed that ~20 micron gramicidin samples gave nice (Laue) diffraction patterns. Next, tests at CHESS on their multipole wiggler showed readily measurable diffraction from a protein crystal specifically at 25keV and 38 keV and led to the ideas of ‘ideal data’ free of absorption errors & of using short wavelength absorption edge resonant scattering, included in the ESRF Foundation Phase Report. But, since cryodata MX measurement proved very effective at controlling radiation damage and various phasing methods developed notably at the Se K edge, the use of high photon energies for MX went 'quiet'. But high pressure MX at ESRF ID30 reinvigorated the topic as did MX phasing at the Xe and Ho K edges (ESRF ID15). We also still don't have a dedicated charge density Beamline, and where 33 keV would help with the ‘ideal data’ required; a proposal to ESRF from ECDM V has been made.

I presented this talk at the American Crystallographic Association Annual Conference held in Albuquerque in 2014. I am uploading this talk now as there is a renewed interest in high photon energies in macromolecular crystallography owing to an interest in ambient temperature data collection.