Jim Clarke

A high-throughput structural biology/proteomics beamline at the SRS on a new multipole wiggler

The North West Structural Genomics Centres beamline, MAD10, at the SRS receives the central part of the radiation fan (0.5 mrad vertically, 4 mrad horizontally) produced by a new 2.46 T ten-pole wiggler. The optical arrangement of the beamline consists of a Rh-coated collimating Si mirror, a fixed-exit-beam double-crystal monochromator with sagittal bending for horizontal focusing and a second Rh-coated Si mirror for vertical focusing. The double-crystal Si (111) monochromator allows data collection in the 5-13.5 keV photon energy range with rapid (subsecond) tunability and high energy resolution. The monochromatic beam is optimized through a 200 microm collimator. The beamline end station has been designed around a Mar desktop beamline with high-throughput cryogenic sample changer, Mar225 CCD detector, liquid-N(2) autofill system and an ORTEC C-TRAIN-04 energy-resolving high-count-rate X-ray fluorescence detector. The instrument is optimized for MAD/SAD applications in protein crystallography with the additional mode of operation of online single-crystal EXAFS studies on the same crystals. Thus, screening of metals/Se in the crystal can be performed quickly prior to MAD/SAD data collection by exciting the crystal with X-rays of appropriate energy and recording an energy-dispersive fluorescence spectrum. In addition, this experimental set-up allows for parallel XAFS measurements on the same crystal to monitor radiation-induced changes, if any, in e.g. the redox state of metal centres to be detected for a metallic functional group during crystallographic data collection. Moreover, careful minimization of the thickness of the Be window maximizes the intensity performance for the 2.0-2.5 A softer wavelength range. This range also covers the K-edges of a number of important 3d transition metals as well as the L-edges of xenon and iodine and enhanced sulfur f .

An XUV-FEL amplifier seeded using high harmonic generation

A detailed design of a free electron laser (FEL) amplifier operating in the extreme ultra violet (XUV) and seeded directly by a high harmonic source is presented. The design is part of the 4th generation light source (4GLS) facility proposed for the Daresbury Laboratory in the UK which will offer users a suite of high brightness synchronised sources from THz frequencies into the XUV. The XUV-FEL will generate photons with tunable energies from 8 to 100u2009eV at giga-watt peak power levels in near Fourier-transform limited pulses of variable polarisation. The designs of the high harmonic generation (HHG) seeding, FEL amplifier and synchronising systems are presented. Numerical simulations quantify the FEL output characteristics.

4GLS—the UK's fourth generation light source at Daresbury: new prospects in biological surface science

4GLS is a suite of accelerator-based light sources planned to provide state-of-the-art radiation in the low energy photon regime. Superconducting energy recovery linac (ERL) technology will be utilized in combination with a variety of free electron lasers (IR to XUV), undulators and bending magnets. The 4GLS undulators will be optimized to generate spontaneous high flux, high brightness radiation, of variable polarization, from 3 to 100xa0eV. The ERL technology of 4GLS will allow shorter bunches and higher peak photon fluxes than possible on storage ring sources. It also provides pulse structure flexibility and an effectively infinite beam lifetime. The XUV and VUV free electron lasers will be used to generate short (femtosecond regime) pulses of extreme ultraviolet light that is broadly tunable and more than a million times more intense than the equivalent spontaneous undulator radiation. A strong feature of the scientific programme planned for 4GLS is dynamics experiments in a wide range of fields. Pump–probe experiments will allow the study of chemical reactions and short-lived intermediates on the timescale of bond breaking and bond making, even from very dilute species. The high intensity of the FEL radiation will allow very high resolution in imaging applications, using near-field approaches. For example, in the IR regime, resolution of the order of 30–50xa0nm should become possible, allowing the sub-cellular structure of live cells to be examined. The combination of high brilliance with short pulse lengths from multiple sources will allow development of techniques that probe the nature of biomolecule interactions with surfaces. These include methods for probing conformational changes on binding such as time-resolved sum-frequency spectroscopy and reflection anisotropy spectroscopy.

Sub‐picosecond X‐rays from CEBAF at Jefferson Lab.

A high brightness sub‐picosecond x‐ray source can be created by installing an undulator at Jefferson Lab’s CEBAF, a nuclear physics electron accelerator. Although the beam current is only 100 microamps, the electron beam has an extremely small emittance and energy spread, with the result that one can produce x‐ray beams tunable over the range 5–30keV with an average brightness quite comparable to beamlines at the Advanced Photon Source (APS) at Argonne National Lab. In addition, with rms bunch lengths measured down to 85 fsecs, peak brightness values are much higher than at the APS. Furthermore, this x‐ray source has similar emittance in both horizontal and vertical directions, (a so‐called round beam) making it of very high potential for many applications. In order to determine if indeed such a source is worth pursuing we present “tuning curve” calculations of peak and average flux and brightness for an undulator on CEBAF. They are compared with similar calculations for a dipole and for undulator‐A at th...

4GLS: the UK’s fourth generation light source

4GLS is a suite of accelerator-based light sources planned to provide state-of-the-art radiation in the low energy photon regime. Superconducting energy recovery linac (ERL) technology will be utilised in combination with a variety of free electron lasers (IR to XUV), undulators and bending magnets. The 4GLS undulators will generate spontaneous high flux, high brightness radiation, of variable polarisation from 3 - 800 eV, optimised in the lower harmonics up to about 200 eV. Viable radiation at energies up to several keV may be provided from multipole wiggler magnet radiation. The ERL technology of 4GLS will allow shorter bunches and higher peak photon fluxes than possible from storage ring sources. It will also give users the added bonuses of pulse structure flexibility and effectively an infinite beam lifetime. VUV and XUV FELs will be used to generate short pulses (in the fs regime) of extreme ultraviolet light that is broadly tuneable and more than a million times more intense than the equivalent spontaneous undulator radiation. A strong feature of the scientific programme planned for 4GLS is dynamics experiments in a wide range of fields. Pump probe experiments will allow the study of chemical reactions and short-lived intermediates on the timescale of bond breaking and bond making, even for very dilute species. The high intensity of the FEL radiation will allow very high resolution in imaging applications. Funding for the first three years of the 4GLS project was announced by the UK Government in April 2003. This includes the research and development work necessary to produce a design study report, with the construction of an ERL-prototype. Additional funds have recently been awarded that will enable a study of the production of ultra-short pulsed X-rays from the ERL-prototype via Thomson scattering. It is anticipated that the full 4GLS facility will be available to users in 2011.

Medical therapy and imaging fixed-field alternating-gradient accelerator with realistic magnets

NORMA is a design for a normal-conducting race track fixed-field alternating-gradient accelerator (FFAG) for protons from 50 to 350 MeV. In this article we show the development from an idealised lattice to a design implemented with field maps from rigorous two-dimensional (2D) and three-dimensional (3D) FEM magnet modelling. We show that whilst the fields from a 2D model may reproduce the idealised field to a close approximation, adjustments must be made to the lattice to account for differences brought about by the 3D model and fringe fields and full 3D models. Implementing these lattice corrections we recover the required properties of small tune shift with energy and a sufficiently-large dynamic aperture. The main result is an iterative design method to produce the first realistic design for a proton therapy accelerator that can rapidly deliver protons for both treatment and for imaging at up to 350 MeV. The first iteration is performed explicitly and described in detail in the text.