Clarke JA

Hannon FE

Scott DJ

English

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THE INITIAL INSERTION DEVICES FOR THE DIAMOND LIGHTSOURCEJ. A. Clarke, F. E. Hannon and D. J. Scott, ASTeC, Daresbury Laboratory, Warrington, UKAbstractThe first eight DIAMOND beamlines have now beenagreed. Insertion devices must be tailored to meet theneeds of each of these beamlines and so it is now clearwhat form the first insertion devices for DIAMOND willtake. Six of the devices will be short period, small gapundulators designed to reach between approximately 5 to20 keV with the use of high harmonics. Four of thesedevices will take advantage of in-vacuum technology toenhance their spectral outputs. One insertion device willbe a superconducting multipole wiggler with a peak fieldof 3.5 T, designed to provide large flux in the 20 to100 keV region. The final insertion device will be avariable polarization undulator providing light in the softX-ray region of 80 to 1500 eV.  This paper will describethe insertion devices selected for each beamline with briefjustification.1  INTRODUCTIONDIAMOND [1] is a 3rd generation synchrotron lightsource for the UK that is optimised for the use ofInsertion Devices (IDs).  Located in the field free spacesof the 5 or 8 m straights these IDs will be the primaryphoton sources for the scientific research programme andthe detailed specification and design of each one will bestrongly related to its scientific application. In September2001 eight beamlines were chosen to be the firstcomplement of beamlines on DIAMOND although it islikely that only seven will be funded immediately (the so-called ‘Day 1’ beamlines). The spectral requirements foreach of these eight beamlines have since been discussedat a number of external working groups with various IDoptions presented. By March 2002 the ID for eachbeamline had been identified.2  INSERTION DEVICE SELECTION2.1  Very High Energy BeamlineThis beamline will support research into materialsunder extreme conditions. The beamline will consist oftwo experimental areas; the first experimental arearequires high flux over 20 to 100 keV and the secondbetween 20 and 40 keV. Each experimental area willaccept 1 mrad of beam, the higher energy one will becentred on axis with the other one being centred 1.5 mradoff axis. The total power produced by the insertion deviceis a concern. Until detailed front end design and opticsdesign has been carried out it has been decided to limitthe power produced by the insertion device to a total of20 kW at 300 mA of beam current.The photon flux over the energy range 20 to 100 keVhas been calculated for superconducting MPWs with apeak magnetic field between 3.0 and 3.5 T. The period ofeach MPW was chosen with reference to a threedimensional magnet model based upon the MAX IIdesign parameters [2]. The ID length was varied as afunction of field and period to limit the total power to20 kW.The results of these flux calculations show thatalthough the 3.0 T SC MPW provides greater flux at20 keV the 3.5 T SC MPW does provide enhanced flux atthe highest energies. The 3.5 T SC MPW has beenselected for this beamline because of the high energyphoton performance and also because the lower energyphotons have a flatter profile with horizontal angle for thesecond (off axis) experimental area. A summary of theparameters for all of the selected IDs will be given inSection 3.2.2  Materials BeamlineThis beamline will be a high resolution diffractionbeamline for the study of materials and magnetism. Theflux transmitted through a 100 µrad (horizontal) x 25 µrad(vertical) beamline aperture has been maximised over therequired photon energy range of between 3.4 and 20 keV.Low divergence of the beam in both planes is essentialand this implies the use of an undulator rather than amultipole wiggler.Three types of undulator have been compared; a 5 mdevice with a 15 mm magnet gap, a 2 m device with a10 mm magnet gap and a 2 m in-vacuum (IV) device with7 mm magnet gap. A direct comparison between theoptimum of each type of undulator is given in Figure 1.The flux into the beamline aperture for undulators with ~3degree phase errors has also been calculated.1E+131E+141E+151E+160 5000 10000 15000 20000Photon Energy (eV)Flux (photons/s/0.1% bw)U27 IV U28, 2mU33, 5mFigure 1. Spectral flux comparison between a 27 mmperiod in-vacuum undulator, a 28 mm period, 2 mundulator and a 33 mm period, 5 m undulator.Proceedings of EPAC 2002, Paris, France2607The lower divergence with the longer ID is significantand this is considered to be sufficiently attractive whencompared to the rather marginal flux differences betweenthe three ID types to tip the balance in favour of the U33,5 m undulator.2.3  Macromolecular BeamlinesThree beamlines will be dedicated to proteincrystallography. The same beamline aperture has beenused to select the ID as for the materials beamline butover the slightly different photon range of 5 to 25 keV.Also, specific key photon energies that correspond toparticular element edges have been identified and the fluxhas been maximised at these values as far as possible. Thethree most important edges are Se K (12.658 keV), Hg L3(12.284 keV) and Pt L3 (11.564 keV). At least one of thethree beamlines is likely to include a side-station at somepoint in the future. This will operate at one or two fixedphoton energies. This is likely to be served by a separateinsertion device in a chicane arrangement.In DIAMOND at photon energies in the range ~100 eVto ~10 keV an undulator generally outperforms a MPW.However, beamlines which demand higher energies thanthis must seriously consider using an MPW. Acomparison between an MPW and an undulator is givenfor this beamline example in Figure 2 where the fluxemitted by the MPW into the small beamline aperture hasbeen calculated. This shows that for small beamlineapertures, of the order of the size of the undulator centralcone, an undulator outperforms the MPW up to ~25 keVin flux terms.1E+111E+121E+131E+141E+151E+160 10000 20000 30000 40000 50000Photon Energy (eV)Flux (photons/s/0.1% bw)3.5 T MPWU23 In VacuumUndulatorFigure 2. Photon flux in the central cone of a 23 mmperiod in-vacuum undulator and integrated over a100 µrad x 25 µrad aperture for a 3.5 T MPW.As for the materials beamline, three types of undulatorhave been compared; a 5 m device with a 15 mm magnetgap, a 2 m device with a 10 mm magnet gap and a 2 m in-vacuum device with a 7 mm magnet gap. In this case theadvantage of the in-vacuum undulator was significant andtherefore  a 23 mm period IV undulator has been selectedfor two out of the three beamlines. The third beamlinewill also be an in-vacuum undulator of the same lengthbut it may opt for a shorter period to enhance the higherenergy radiation at the expense of tunability. Then, ifDIAMOND performs beyond the present specificationand allows the 7 mm minimum gap to be reduced furtherduring operations a shorter period device would havesignificant advantage. This is a somewhat risky approachbut can be justified for a user community which has threevery similar beamlines.2.4  Microfocus XAS BeamlineThis beamline will be a medium energy microfocusbeamline for X-ray spectroscopy. An undulator isproposed because high flux levels are required in a smallphase space area with minimal power being absorbed bythe beamline elements. The flux generated by theundulator in the central cone has been maximised over thebeamline photon energy range of the beamline, which isbetween 1.5 and 20 keV. The advantage of the in-vacuumundulator is significant and therefore a 27 mm period IVundulator has been selected for this beamline.2.5  SXR for Nanostructures BeamlineThis will be a soft X-ray beamline dedicated to thestudy of nanostructures. An undulator is required that canprovide variable polarization and high flux over the primeenergy range of the beamline which is between 200 eVand 1300 eV. In particular, left and right circular andlinear horizontal and vertical are required to be available.The photon energy range in linear polarisation modeneeds to be wider, covering 80 to 1500 eV.An APPLE 2 device has been assumed for thisbeamline as it matches the ID requirements well. Oncethe decision for the APPLE 2 technology is made thechoice of period is quite straightforward. In fact, therequirement for horizontal polarization down to 80 eV isthe limiting factor and this requires a period of 64 mm fora 5 m device with a 15 mm gap.2.6  Non-Crystalline Diffraction BeamlineThis beamline will be dedicated to non-crystallinediffraction. The same beamline aperture has been used toselect the ID as for the materials beamline but over theslightly different photon range of 6.5 to 20 keV. Thebeamline must also be able to operate at one key photonenergy that does not fall within the photon energy range,the Calcium K edge (4.04 keV). Low divergence of thebeam in both planes is necessary in order to minimise thesmearing at the detector and this  implies the use of anundulator rather than a multipole wiggler.As for the materials beamline, three types of undulatorhave been compared. The 5 m, 15 mm gap device wasrejected because of the relatively poor performance at thehigh photon energy end. Also, the advantage of the in-vacuum undulator is not considered significant in thiscase when compared to the increased cost and risk to thestorage ring vacuum and therefore a 27 mm periodconventional undulator has been selected for thisbeamline.Proceedings of EPAC 2002, Paris, France26083  SUMMARYTable 1 summarises the proposed first eight insertiondevices for ‘Day 1’ operation on DIAMOND and thebrightness of all of these devices is plotted in Figure 3.Each of the IDs has been selected after extensiveconsultation with the anticipated user communities. Thebeamline energy ranges are dominated by a majoritywanting to cover from a few keV to ~20 keV. These willall be met by short period, small gap undulators workingat high harmonics. To provide the best quality radiation atthese high photon energies, four of the first eight IDs willbe in-vacuum undulators.The procurement phase for DIAMOND has now startedand these IDs must be available for installation by aboutthe end of 2005. The selection process for the next batchof beamlines has already started and it is anticipated thatbetween 2 and 4 additional IDs will be required per yearduring the first few years of operation.4  REFERENCES[1] V. P. Suller, "Status of the DIAMOND Project", theseproceedings.[2] D. Leblanc et al, "The Max Wiggler", Proc EPAC2000, pp2334-2336.Table 1. Summary of the parameters of the first insertion devices for DIAMOND.Name Beamline Technology BMax(T)KMax Period(mm)NPeriods Length(m)MPW60 VHE SC MPW 3.5 19.6 60 16 1.0U33 Materials Und 0.54 1.66 33 149 5.0U23 IV a PX IV Und 0.70 1.49 23 85 2.0U23 IV b PX IV Und 0.70 1.49 23 85 2.0U23 IV c PX IV Und 0.70 1.49 23 85 2.0U27 IV XAS IV Und 0.80 2.02 27 72 2.0HU64 SXR Helical Und 0.57 3.4 64 75 5.0U27 NCD Und 0.70 1.76 27 72 2.01E+161E+171E+181E+191E+201E+21100 1000 10000 100000Photon Energy (eV)Brightness (photons/s/mm2 /mrad2/0.1% bw)MPW60HU64U23 IVU33U27U27 IVFigure 3. The spectral brightness for the first insertion devices for DIAMOND.Proceedings of EPAC 2002, Paris, France2609

The initial insertion devices for the Diamond Light Source

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