Kirrily Rule 2013-04-09 16:47 When using the 12T magnet on TAIPAN, you must work in fixed Ki mode, as the magnet is too heavy to move M2. Consider the energy transfer range required to determine the appropriate Ei for these experiments. After discussing your instrument preferences with your local contact, they will align the spectrometer in the following way: Drive the spectrometer to the required incident energy (for elastic mode) = e.g. 14.87meV Drive the analyser arm to the straight-through position (s2=0, a1=0, a2=0, atrans=19) Visually check the straight-through arm and change any motors accordingly Place the Ni sample on the sample stage, and Borated Al sheets over the analyser collimator. (the detector saturates at ~35,000 counts/sec) Check M1 alignment with a rocking scan Check S2=0 alignment with a rocking scan Check A2=0 alignment with a rocking scan Remove the Al attenuator and insert collimators if they need changing Perform the Ni powder calibration, using 5 peaks From the least squares fitting of these peaks, update the new M1 offset, M2 offset and S2 offset. With the spectrometer at S2=-50, and atrans=0 (to view the Vanadium incoherent peak from the Ni sample can), perform an A1 scan and an A1/A2 scan around the elastic position. Perform an En scan (where Ei will move if Ef is fixed). Here the FWHM of the peak will give you the resolution of your instrument. Currently the continuous focusing mechanism is not implemented on Taipan. If you wish to use focusing for your inelastic measurement, consider the following parameters sets. Focus condition mvfocus mhfocus avfocus ahfocus Flat 50 220 0 0 Optimal for 14.87meV 125 155 125 80 Optimal for 30.5meV 150 170 180 65 At the beginning of an experiment load the “Experimental setup” script (in the scripts window, right screen) to list the most important configuration identifiers for the experiment. These should appear in the header lines in your data files. For instance, these include: Proposal number and title User’s name, and research team present Local contact’s name Sample information including number of samples and sample environment requirements Particular instrument setup features (scattering sense, collimation, filters, slits etc) Next the UB matrix needs to be set. To do this, you need to input the cell parameters and at least 2 reflections which will define your scattering plane. These can be calculated for your system using the file “/home/taipan/calculatedDspaceTAIPAN.xls” or something similar, such as the ICSD website. > tasub listub shows the current UB matrix, cell parameters and reference peaks > tasub cell a b c alpha beta gamma input new lattice parameters > tasub addref qh qk ql adds a new reflection to the list when Taipan is at the reflection > tasub addref qh qk ql a3 a4 sgu sgl ei ef adds a new reflection from a calculation > tasub addauxref qh qk ql adds a new reflection where S2 is calculated from the lattice parameters only. This will also calculate the relative S1 positions > tasub del num deletes one of the previously stored reflections > tasub listref lists the reflections that have been input > tasub makeub 1 2 calculates new UB matrix from reflections 1 and 2 > tasub calcang qh qk ql ei ef calculates reflection from UB matrix – be careful when changing lattice parameters, as this command won’t use them! Output: M2 S1 S2 sgu sgl A2 For Ei = Ef = 14.87 meV > tasub cell 5.011 5.85 10.353 90 92.4 90 > tasub calcang 1 0 0 14.87 14.87 (calculated S2 = 27.1) > tasub calcang 1 1 0 14.87 14.87 (calculated S2 = 35.9) > tasub calcang 0 2 0 14.87 14.87 (calculated S2 = 47.3) Drive the instrument to the calculated S2 value of a particular peak. The other motor positions are not correctly set at this point. This will also give you a relative s1 position between the peaks. Scan S1 until you find the peak. > bmonscan clear > bmonscan add S1 -10 0.2 (motor name, starting point, step size) > bmonscan run 60 timer 5 (scans 60 points, for a time of 5 seconds per point) OR > runscan s1 -10 0 101 time 5 (motor, start, stop, # pts, time (the mode in secs)) (this does not work for multiple motors yet) (This step should hopefully be replaced by the differential scan, or the rate-meter) Once the peak position (S1) has been optimised, scan sgu and sgl > runscan sgl -10 10 21 time 1 > runscan sgu -10 10 21 time 1 Once the peak has been optimised with SGU and SGL (and you are sitting at the peak position!!) you can set this as one of your reference peaks, where the current motor values define the peak position. > tasub addref 1 0 0 Calculate the values of S1 and S2 for the next peak – use the > tasub calcang qh qk ql ei ef command to see the relative values of S1 and S2 as calculated from the lattice parameters! Repeat for at least one other peak, preferably one orthogonal to the first. > tasub addref 0 0 1 > tasub listref (to see the observed peaks in your list (e.g. number 4 and 5)) > tasub makeub 4 5 (this used peaks 4 and 5 to calculate the UB matrix) > tasub update > tasub listub Once this has been set, then you should be able to drive your spectrometer to any accessible qh, qk, ql and en. At the end of each change, be sure to type > tasub update Once your sample has been aligned, add the PG filter to the instrument. You could test the effectiveness of the filter by scanning a peak that will display higher order scattering – e.g. (½ 0 0) which does not exist except from higher order scattering from the (1 0 0 ). Sometimes you might want to add an additional filter. Finally you can scan your slits to reduce the background scattering. > runscan pa_left -15 -2 27 time 1 (scans 27 points, for a time of 1 seconds per point) After this, consider if you need to add more shielding to the detector drum or any other part of the instrument (e.g. manual slits on analyser arm, additional PG filters). During your experiment you may need to change the lattice parameters (due to a phase transition, thermal expansion etc). If this is the case you MUST find and optimise two new reflections to make your UB-matrix from. For example, scan a Qh peak as follows: > drive qh 4 qk 0 ql 0 en 0 > runscan qh 3.985 4.015 31 time 5 The centre of this scan should be close to 4, but could be shifted. This will be the fit value from the scan. Then you can change the a lattice parameter accordingly in tasub anew=aold(peakcalculated/peakcentre from scan) a n e w = a old ( ⁢ peak calculated peak centre from scan ) > tasub cell a b c alpha beta gamma The next peak can be aligned in the same way > drive qh 0 qk 4 ql 0 en 0 > runscan qk 3.985 4.015 31 time 5 Once you have changed your unit cell parameters, you need to add the two new peaks into your reference list, optimise the goniometers again and re-make your UB matrix with these new peaks > tasub cell 3 9 15 90 90 90 > tasub cell 2.9 8.7 14.5 90 90 90 > tasub addauxref 0 0 4 > tasub addauxref 0 4 0 NO QH QK QL S1 S2 SGU SGL EI EF 1 0.00 0.00 4.00 22.62 -27.10 0.00 0.00 25.86 14.87 (old lattice parameters) 2 0.00 4.00 0.00 -65.74 -51.21 0.00 0.00 25.86 14.87 (old lattice parameters) 3 0.00 0.00 4.00 -156.85 -28.38 0.00 0.00 25.86 14.87 (new lattice parameters) 4 0.00 4.00 0.00 -66.10 -53.30 0.00 0.00 25.86 14.87 (new lattice parameters) You can see already that by changing the lattice parameters the scattering angles change. So you need to optimise these peaks again, as before and add the new reflections to the list before re-making your UB-matrix. If your sample is cubic (and remains cubic at low temperatures) and you are in the HK0 scattering plane, then the lattice parameters are best set with a peak that involved both H and K – for instance the 110 peak. Make sure after you have changed your lattice parameters, and both peaks have been added to the reference list that you remake your ub matrix!