STATION 6.2
High Time Resolution Materials Processing - MPW6.2

Description

MPW6.2 is one of the most recently commissioned stations on the SRS (2003). It is a materials science station dedicated to the study of time-resolved variation of short and/or long-range order in a variety of inorganic and organic materials. It is particularly suited to experiments where the timescales of interest are in the millisecond and second regions and/or where a selectable energy is required.

The beamline can be configured in one of two principal modes:

1. time-resolved, medium resolution X-ray Powder Diffraction (XRD)
2. time resolved Non-Crystalline Diffraction (NCD), i.e. simultaneous Small-Angle X-ray Scattering and Wide-Angle X-ray Scattering (SAXS/WAXS)

A third option of Extended X-ray Absorption Fine Structure (EXAFS) is potentially possible, but has not been commissioned and is not offered at the moment.
Due to the complexity of the changeover between the two modes, beamtime is normally scheduled to accommodate one block of time in each mode per Allocation Period of 6 months.

The source is a Mutli-Pole Wiggler (MPW) insertion device and the energy used can be selected within the range 5 keV to 18 keV. The standard energy delivered by the station (that is, unless specifically requested prior to the beamtime by the User) is 8.865 keV (λ = 1.40 Å). At this energy the output from the insertion device and the detectors’ efficiencies are optimised.

The intense X-ray source is complemented by a matched pair of state-of-the-art 1-dimensional SAXS and WAXS detectors. The detectors can be used individually or as a synchronised pair, depending on the station’s configuration and experimental requirements.

Control of beamline elements, data acquisition and sample environments (where these have been integrated) is via the Generic Data Acquisition (GDA) software, which allows fully synchronised, single interface control of the experiment and its parameters.

A variety of sample environments have been commissioned and are available for use in either of the standard configurations. Users may also bring their own sample environments, subject to compatibility and safety considerations and the prior agreement of the station scientist.

In the Proposed SRS Station Closure Plan published in September 2005 (Recent User Communications) the closure date of MPW6.2 was announced as 31^st December 2008, when the SRS itself will cease operations.

News

January 2008
Latest version of the GDA installed – v7.2.0.
Cordless telephone installed in the Experimental Hutch.
Hands-free telephone installed in the Control Cabin.
2 additional emergency stops for the Parker stepper motors installed in the Experimental Hutch.
MPW6.2 will finally cease User operations on September 30th 2008.  The last currently scheduled day of multi-bunch operations is 1st August 2008.

August 2007
Latest version of the GDA installed – v6.12.0.
3 pan-tilt-zoom webcams installed in the Experimental Hutch.
Automatic sample changer for SAXS commissioned.
Double-screen layout for the sample environment PC installed.

August 2006
Latest version of the GDA installed: v6.8.0 now running on a Linux platform with undockable function tabs and a double screen layout.
New SUN PC installed running on a Linux platform.
Dedicated User's PC installed running under Windows.
New colour printer installed.
Small library of textbooks now provided for User's reference.
HATSAXS project approved whereby after closure of the SRS MPW6.2 will transfer onto Diamond.

Functional Description

The combination of a high-flux source, tuneable energy, high-efficiency 1–dimensional position-sensitive detectors and integrated control software allows MPW6.2 to offer unique opportunities for time-resolved studies in materials science where the timescales of interest are in the millisecond to second region. However, the instrumentation is ultimately capable of operating in the tens of microseconds region.

In X-ray powder diffraction (XRD) configuration the medium-high resolution curved 1-dimensional wide-angle X-ray scattering (WAXS) detector (which is based on RAPID2 technology – wire micro-gap gas detector with ADC per channel ) is capable of handling the very high intensity diffracted X-rays without attenuating the incident beam. This enables very high time resolutions to be achieved with the capability of distinguishing structural and phase changes during kinetic experiments. The resulting data is often analysable using Rietveld refinement techniques. The curved WAXS detector has an acceptance angle of 60 degrees 2θ and is mounted on the 2θ arm of a high-resolution diffractometer, which has a usable 60 degree rotation. At the centre of rotation of the 2θ arm is an Omega stage on which samples or sample environments are often mounted.

A variety of sample environments for XRD experiments are available, including capillary and flat-plate furnaces, cryostream, cryostat and hot-air gun. Many Users have developed their own specialised sample environments and these can often be accommodated, but in these cases are encouraged to discuss their requirements with the station scientists well in advance of any beamtime and preferably before making a new application.

In Non-Crystalline Diffraction (NCD) configuration the WAXS detector is mounted rigidly onto a nosecone sited adjacent to the sample position and in this position it has an acceptance angle of 7 degrees to 67 degrees in 2θ in the upwards vertical plane. Beyond the nosecone a variable-length evacuated small-angle X-ray scattering (SAXS) camera tube is fitted, with stepwise length variations between ~1.3 and ~4.00 metres possible, in 0.25 metre steps. At the end of the SAXS tube a second 1-dimensional small-angle detector is placed which is aligned to be effective in the downward vertical plane. The SAXS detector utilises a standard aperture design of a 60 degree quadrant and is functionally complementary to the curved WAXS detector enabling truly synchronised SAXS and WAXS measurements to be made. Users have the option of only utilising the SAXS detector, of course.

A variety of sample environments for NCD experiments are available, including Linkam DSC, Linkam capillary hot stage, high-temperature furnace, 4-syringe stopped-flow mixer, liquid cells and water baths. Many Users have developed their own specialised sample environments and these can often be accommodated, but in these cases are encouraged to discuss their requirements with the station scientists well in advance of any beamtime and preferably before making a new application.

A feature of the station is its energy tunability and for this a double-bounce, double silicon crystal monochromator is used. Any energy between 5 and 18 keV may be chosen but Users should be aware that the photon flux and detector efficiencies are maximised in the range of 8-9 keV. The standard energy offered is 8.865 keV (1.40 Å). The monochromator’s second crystal is a thin wafer which is sagitally bent to provide horizontal focussing anywhere between the sample position and the maximum SAXS detector position at +4 metres. As a change in energy (or a change in SAXS camera tube length) requires re-optimisation of the station optics and realignment of the detectors, it is not generally possible to effect an energy change during a single beamtime.

The GDA software is installed on the station for data acquisition and, in many cases, control of the experiment. This is advanced software based on a Graphical User Interface (GUI) and is designed around the principle of utilising a single piece of software to integrate with, and to control, all the normal experimental functions and equipment as well as the station set-up. Users configure their data acquisition protocols and can control sample environment parameters, where these environments have been integrated, from within the single GUI. Accurate synchronisation and control of experiments are thus assured.

Potential Users should be aware that as MPW6.2 is a high flux station optimised for time-resolved experiments, beamtime is unlikely to be granted for static measurements.

Technical Description

The total radiation fan from the multi-pole wiggler (MPW) on beamline 6 is split into two sections 9.8 m from the tangent point where a plane mirror deflects 7.5 mrad of the beam in the UV range for use in MPW6.1. Station MPW6.2 receives a horizontal fan of radiation from 0.5 to 4.5 mrad and a vertical fan of 1.4 mrad as defined by a water cooled aperture at 12.88 m. This produces a beam 3.8 mm high and 67.5 mm wide at the first optical element – a plane cylindrically-bent Si mirror (1220 mm x 120 mm x 50 mm with a 500 Å rhodium coating) that is water cooled. This is placed 14.425 m from the source and is bent to achieve a vertically parallel beam. The collimated beam then falls onto a two-crystal Si(111) monochromator that is 15.98 m from the source.. The first crystal is flat and water cooled and allows the selection of any energy in the range 5-18 keV (2.5-0.69 Å). The second crystal is a thin wafer which has 3 longitudinal ribs and can be sagitally-bent for horizontal focussing. The degree of bend on the second crystal allows the full incident fan to be focussed horizontally to ~1.3 mm (fwhm) at any point in the experimental hutch over a range of 5 m. A second plane Si/Rh mirror, identical to the first, is situated 17.965 m from the source and is used to provide vertical focussing of the beam to ~300 μm (fwhm).

A complementary pair of 1-dimensional wide- and small-angle detectors (as described in the section “Functional description”) with RAPID2 electronics as the readout system operate at very high count rates, resulting in short data collection times without the need for attenuating the incident beam. A pair of (unmatched) air-gap ion chambers are available for coarse X-ray spectroscopic measurements and X-ray beam intensity monitoring.

• Focussing optics: 2 plane Si/Rh mirrors for vertical focussing. A 2-crystal, double-bounce, saggitally-bent Si (111) monochromator for energy selection and horizontal focussing.
• Collimation: 5 pairs of horizontal and vertical slits, the final pair being just before the sample position.
• Bandpass (monochromatisation):ΔE/E ~10^-4. Photon flux ~e¹² photons/s/0.01% bandpass at 200mA stored beam current. Photon flux is energy-dependent and is peaked at 8-9 keV.
• Beamsize at focus ~1.3 x 0.3 mm² (H x V).
• Energy range: 5 – 18 keV.
• X-ray detection system: 2 1-dimensional WAXS and SAXS detectors based on RAPID2 technology (gas microgap, multi-wire). Efficiency is energy-dependent and is peaked at 8-9 keV. The WAXS detector has an acceptance angle of 60° 2θ and a resolution of ~0.06°. Minimum SAXS camera tube length is 1.3 m, maximum is 4.0 m with a maximum resolution of ~800 Å at λ = 1.40 Å.
• Experimental configurations: Medium-high resolution powder diffraction based on a 2-circle diffractometer OR simultaneous SAXS and WAXS.

Development

The station actively operates a continual-development approach. This includes sample environments, detectors, software and User facilities. Users are encouraged to develop their own sample environments specific to their particular experimental requirements and the station has a very active programme in this area. It is often possible to integrate the control of these environments into the station’s GDA software for precise control.

Proposed Developments

Technical developments will transfer directly to the facilities currently being built and planned at Diamond Light Source Limited (DLS) when the station ultimately closes on 30th September 2008 and as such will continue to benefit the station’s current User community. The XRD component of the MPW6.2 facility will transfer to I11
(see http://www.diamond.ac.uk/Beamlines/Beamlineplan/I11/default.htm) and the NCD component to I22 (see http://www.diamond.ac.uk/Beamlines/Beamlineplan/I22/default.htm). Users are encouraged to make early contact with the respective Beamline Scientists at DLS to ensure a smooth transition of their experimental programmes to the new facilities.

Benchmark

The flux at the focal point for the full fan from the insertion device is ~2.5x10¹² photons s^-1, measured at a 200 mA stored beam current and an energy of 8.856 keV (λ – 1.40 Å). The fwhm dimensions of the beam under these conditions are 1.3 x 0.3 mm² (H x V).

Set-up Time

• To change station’s configuration from XRD to NCD or vice-versa takes 3-4 days.
• In XRD mode, to change the energy and re-optimise the optics takes ~6 hours.
• In NCD mode, to change energy and/or SAXS camera length and to re-optimise the optics takes 8-10 hours, depending on the complexity of the set-up.

Users should note that:

• Energy/camera length changes will not normally be considered during beamtime. If this is essential in order to meet experimental requirements, 1 extra day must be requested on the Beamtime Application Form specifically for this purpose.
• In principle, station set-up time forms part of the User’s beamtime allocation made by the Facilities Access Panel (FAP) and Users must take this into account when applying for beamtime.

Applying for Beamtime

Beamtime at the SRS is allocated in six-monthly cycles and the deadlines for the receipt of applications for beamtime are 1^st May and 1^st November. The application process is described in detail in the User Liaison Office’s (ULO) web pages; please see http://srs.dl.ac.uk/ULO/index.htm, and Users are strongly recommended to read this information carefully before submitting their application.

Potential applicants to MPW6.2 should read the relevant sections of the current web pages to assure themselves that the instrument is suitable for their purposes. If there is any doubt, or Users have any questions regarding the station or the technical aspects of their application, they should contact either of the station scientists for advice. Procedural enquiries should be addressed to the ULO. It is important that the sections in the application form dealing with the requirements for the station’s set up are completed accurately and fully. For instance, with respect to energy and sample environment requirements (station or User’s environments), etc. Users should also be careful to indicate the configuration of the beamline they would like to use; i.e. XRD or SAXS/WAXS. If SAXS or SAXS/WAXS is proposed, then a clear indication of the SAXS resolution range of interest should be made.

Where Users are developing their own sample environments it is essential that they contact the station scientists for advice before applying for beamtime. If beamtime is awarded it is strongly advised that early contact is made so that arrangements can be put in place to ensure there is minimal loss of beamtime in installation, commissioning and testing the equipment.

It should be noted that the time required to set the station up in preparation for the experiment (including changes between consecutive Users, but not changes between major station configurations) is part of the beamtime which is allocated by the Facilities Access Panel (FAP). Users should refer to the “Set-up time” section of these web pages and make an allowance in the time requested to accommodate the setting up of the station. It should also be noted that as a change in energy (or a change in SAXS camera tube length) requires re-optimisation of the station optics and realignment of the detectors, it is not generally possible to effect an energy change during a single beamtime.

Users should note that MPW6.2 is a high flux station optimised for time-resolved experiments and that, whilst in the discretion of the FAP, beamtime is unlikely to be awarded to applicants whose proposal involves all, or in substantial part, static measurements.

Downloadable beamtime application forms are available at http://www.srs.dl.ac.uk/ulo/forms_reports.html. To aid the peer-review and scheduling processes, applicants are requested to include an appropriate completed Supplementary Questionnaire with their application. In addition, the ULO routinely send an email to the Principal Investigator to confirm receipt of the application and Users are recommended to respond to the ULO's email with details of dates which will be unsuitable should beamtime be awarded. These responses will always be taken into account but it cannot be guaranteed that it will be possible to comply. No response will be interpreted as any dates being suitable. Users are also reminded that the considerable effort required to change between the two configurations of the station means that beamtime is scheduled in blocks and so this will severely limit the scope of flexibility in beamtime scheduling.

Applicants are reminded that the phased closure of stations at Daresbury has begun and in particular that from AP46 (September 2005 to March 2006, inclusive) stations 16.1 (NCD) and 2.3 (XRD) in the Materials and Engineering College portfolio of stations will no longer be available. However, stations 2.1 (NCD) and 9.1 (XRD) will remain available until December 2008 and July 2008 respectively. Details of the closure plan can be viewed at http://www.srs.ac.uk/srs/user_news/recent_user_communications.htm and outline information of the SRS to Diamond transition can be viewed at http://www.srs.ac.uk/srs/news_extras/news05/transition.htm. For updates on the progress of facilities at Diamond Light Source Limited (DLS) the DLS web pages should be consulted at http://www.diamond.ac.uk/default.htm. The XRD component of the MPW6.2 community is expected to transfer to I11 and the NCD component to I22.

Technical papers published

MPW6.2
“X-ray beam characteristics on MPW6.2 at the SRS” , Tang, C.C., Martin, C.M., Laundy, D., Thompson, S.P., Diakun, G.P. and Cernik, R.J., Nucl. Instr. and Meth. in Phys. Res. B (2004), 222, 659-666.

“The new materials processing beamline at the SRS Daresbury, MPW6.2” , Cernik, R.J., Barnes, P., Bushnell-Wye, G., Dent, A.J., Diakun, G.P., Flaherty, J.V., Greaves, G.N., Heeley, E.L., Helsby, W., Jacques, SA.D.M., Kay, J., Rayment, T., Ryan, A., Tang, C.C. and Terrill, N.J., J. Synchrotron Rad. (2004), 11, 163-170.

RAPID2 detector system
“The Rapid2 X-ray detection system ”, Berry, A., Helsby, W.I., Parker, B.T., Hall, C.J., Buksh, P.A., Hill, A., Clague, N., Hillon, M., Corbett, G., Clifford, P., Tidbury, A., Lewis, R.A., Cernik, R.J., Barnes, P. and Derbyshire, G.E., Nuc. Instr. and Meth. in Phys. Res. A (2003), 513, 260-263.

“The RAPID2 interpolating system” , Helsby, W.I., Berry , A., Buksh, P.A., Hall, C.J. and Lewis, R.A., Nuc. Instr. and Meth. in Phys. Res. A (2003), 510, 138-144.

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