cbcd98c10c
This directory was accidentally omitted from the merge-release branch during the PSI code merge.
413 lines
21 KiB
XML
413 lines
21 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<?oxygen RNGSchema="http://www.oasis-open.org/docbook/xml/5.0/rng/docbook.rng" type="xml"?>
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<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink"
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version="5.0">
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<info><title>Preparing the spectrometer</title><author>
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<personname>Kirrily Rule</personname>
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</author>
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<date>2013-04-09 16:47</date>
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</info>
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<sect1>
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<title>Aligning the spectrometer</title>
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<warning>
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<title>12T magnet</title>
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<para> When using the 12T magnet on TAIPAN, you must work in fixed Ki mode, as the
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magnet is too heavy to move M2. Consider the energy transfer range required to
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determine the appropriate Ei for these experiments. </para>
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</warning>
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<para>After discussing your instrument preferences with your local contact, they will align
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the spectrometer in the following way:</para>
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<itemizedlist>
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<listitem>
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<para>Drive the spectrometer to the required incident energy (for elastic mode) =
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e.g. 14.87meV</para>
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</listitem>
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<listitem>
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<para>Drive the analyser arm to the straight-through position (s2=0, a1=0, a2=0,
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atrans=19)</para>
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</listitem>
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<listitem>
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<para>Visually check the straight-through arm and change any motors
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accordingly</para>
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</listitem>
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<listitem>
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<para>Place the Ni sample on the sample stage, and Borated Al sheets over the
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analyser collimator. (the detector saturates at ~35,000 counts/sec)</para>
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</listitem>
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<listitem>
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<para>Check M1 alignment with a rocking scan</para>
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</listitem>
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<listitem>
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<para>Check S2=0 alignment with a rocking scan</para>
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</listitem>
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<listitem>
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<para>Check A2=0 alignment with a rocking scan</para>
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</listitem>
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<listitem>
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<para>Remove the Al attenuator and insert collimators if they need changing</para>
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</listitem>
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<listitem>
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<para>Perform the Ni powder calibration, using 5 peaks</para>
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</listitem>
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<listitem>
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<para>From the least squares fitting of these peaks, update the new M1 offset, M2
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offset and S2 offset.</para>
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</listitem>
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<listitem>
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<para>With the spectrometer at S2=-50, and atrans=0 (to view the Vanadium incoherent
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peak from the Ni sample can), perform an A1 scan and an A1/A2 scan around the
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elastic position.</para>
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</listitem>
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<listitem>
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<para>Perform an En scan (where Ei will move if Ef is fixed). Here the FWHM of the
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peak will give you the resolution of your instrument.</para>
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<para/>
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</listitem>
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</itemizedlist>
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<para></para>
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<para></para>
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<para></para>
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<para></para>
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<para></para>
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<para></para>
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<para></para>
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<para/>
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<para/>
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<para/>
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<para/>
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</sect1>
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<sect1>
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<title>Focusing monochromator and analyser</title>
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<para> Currently the continuous focusing mechanism is not implemented on Taipan. If you wish
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to use focusing for your inelastic measurement, consider the following parameters sets. </para>
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<para>
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<table frame="all" >
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<title></title>
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<tgroup cols="5">
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<colspec colname="c1" colnum="1"/>
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<colspec colname="c2" colnum="2"/>
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<colspec colname="c3" colnum="3"/>
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<colspec colname="c4" colnum="4"/>
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<colspec colname="c5" colnum="5"/>
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<thead>
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<row>
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<entry>Focus condition</entry>
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<entry>mvfocus</entry>
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<entry>mhfocus</entry>
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<entry>avfocus</entry>
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<entry>ahfocus</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>Flat</entry>
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<entry>50</entry>
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<entry>220</entry>
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<entry>0</entry>
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<entry>0</entry>
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</row>
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<row>
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<entry>Optimal for 14.87meV</entry>
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<entry>125</entry>
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<entry>155</entry>
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<entry>125</entry>
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<entry>80</entry>
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</row>
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<row>
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<entry>Optimal for 30.5meV</entry>
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<entry>150</entry>
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<entry>170</entry>
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<entry>180</entry>
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<entry>65</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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<warning>
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<title/>
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<para>When driving Ei or Ef in this stage of the setup, the software calculates a
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constant-Q instrument position based on the current UB matrix (usually from the
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previous experiment). This will often drive S1, S2, sgu and sgl to unexpected
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positions. To constrain these so that they don’t move unexpectedly, fix the motors
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so they don't move. </para>
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<para>Motors can be fixed (1) or unfixed (-1) and their status checked by typing the
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motor name </para>
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<para><command>> S1 fixed 1 (fixes S1) </command></para>
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<para><command>> S1 fixed -1 (unfixes S1)</command></para>
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<para>Alternatively you can drive vei which drives only the M1 and M2 motors – this
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cannot be used in a scan command. </para>
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<para><command>> drive vei 14.87 </command></para>
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<para><command>> tasub update </command></para>
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<para><command>> ei </command></para>
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<para/>
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</warning>
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<warning>
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<title/>
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<para>You will often need to “home” the slits if they have been unplugged or removed
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during the setup. The pa_left and pa_right slits can vary between -27 (open) and 0
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(closed), while the pa_top and pa_bottom slits can vary between -200 (open) and 0
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(closed). The same limits apply for the ps_slits. </para>
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<para><command>> pa_left homerun 1 </command> (this will do all of the slits)</para>
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</warning>
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<para/>
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<para>Confirm the following setup for your experiment. </para>
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<para><command>> tasub ss </command> (Scattering sense = M+1, S-1, A+1) </para>
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<para><command>> tasub ana ss </command> (Scattering sense = M+1, S-1, A+1) </para>
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<para><command>> tasub outofplane </command> (Confines the scattering sense to be in the
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plane) </para>
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<para><command>> tasub const </command> (Defines whether Ei or Ef are fixed, or if both
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are fixed) </para>
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<para/>
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</sect1>
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<sect1>
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<title>Aligning your sample</title>
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<para> At the beginning of an experiment load the “Experimental setup” script (in the
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scripts window, right screen) to list the most important configuration identifiers for
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the experiment. These should appear in the header lines in your data files. For
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instance, these include: </para>
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<itemizedlist>
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<listitem>
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<para>Proposal number and title</para>
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</listitem>
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<listitem>
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<para>User’s name, and research team present</para>
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</listitem>
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<listitem>
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<para>Local contact’s name</para>
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</listitem>
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<listitem>
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<para>Sample information including number of samples and sample environment
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requirements</para>
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</listitem>
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<listitem>
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<para>Particular instrument setup features (scattering sense, collimation, filters,
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slits etc)</para>
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</listitem>
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</itemizedlist>
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<para>Next the UB matrix needs to be set. To do this, you need to input the cell parameters
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and at least 2 reflections which will define your scattering plane. These can be
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calculated for your system using the file “/home/taipan/calculatedDspaceTAIPAN.xls” or
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something similar, such as the ICSD website. </para>
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<variablelist>
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<varlistentry>
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<term><command>> tasub listub</command></term>
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<listitem>
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<para>shows the current UB matrix, cell parameters and reference peaks</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub cell a b c alpha beta gamma</command>
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</term>
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<listitem>
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<para> input new lattice parameters</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub addref qh qk ql</command></term>
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<listitem>
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<para> adds a new reflection to the list when Taipan is at the reflection</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub addref qh qk ql a3 a4 sgu sgl ei ef</command></term>
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<listitem>
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<para> adds a new reflection from a calculation</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub addauxref qh qk ql</command></term>
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<listitem>
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<para> adds a new reflection where S2 is calculated from the lattice parameters
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only. This will also calculate the relative S1 positions</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub del num</command></term>
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<listitem>
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<para> deletes one of the previously stored reflections</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub listref</command></term>
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<listitem>
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<para> lists the reflections that have been input</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub makeub 1 2</command></term>
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<listitem>
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<para> calculates new UB matrix from reflections 1 and 2</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>> tasub calcang qh qk ql ei ef</command></term>
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<listitem>
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<para> calculates reflection from UB matrix – be careful when changing lattice
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parameters, as this command won’t use them! Output: M2 S1 S2 sgu sgl
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A2</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<example>
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<title>Sample alignment</title>
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<para> For Ei = Ef = 14.87 meV</para>
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<para><command>> tasub cell 5.011 5.85 10.353 90 92.4 90</command>
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</para>
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<para><command>> tasub calcang 1 0 0 14.87 14.87 (calculated S2 = 27.1) </command></para>
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<para><command>> tasub calcang 1 1 0 14.87 14.87 (calculated S2 = 35.9) </command></para>
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<para><command>> tasub calcang 0 2 0 14.87 14.87 (calculated S2 = 47.3) </command></para>
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<para>Drive the instrument to the calculated S2 value of a particular peak. The other
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motor positions are not correctly set at this point. This will also give you a
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relative s1 position between the peaks.</para>
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<para>Scan S1 until you find the peak. </para>
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<para><command>> bmonscan clear</command></para>
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<para><command>> bmonscan add S1 -10 0.2 </command> (motor name, starting point, step
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size)</para>
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<para><command>> bmonscan run 60 timer 5 </command> (scans 60 points, for a time of 5
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seconds per point)</para>
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<para>OR</para>
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<para><command>> runscan s1 -10 0 101 time 5 </command> (motor, start, stop, # pts,
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time (the mode in secs))</para>
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<para>(this does not work for multiple motors yet)</para>
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<para> (This step should hopefully be replaced by the differential scan, or the
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rate-meter) </para>
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<para>Once the peak position (S1) has been optimised, scan sgu and sgl </para>
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<para><command>> runscan sgl -10 10 21 time 1 </command></para>
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<para><command>> runscan sgu -10 10 21 time 1 </command></para>
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<para>Once the peak has been optimised with SGU and SGL (and you are sitting at the peak
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position!!) you can set this as one of your reference peaks, where the current motor
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values define the peak position. </para>
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<para><command>> tasub addref 1 0 0 </command></para>
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<para>Calculate the values of S1 and S2 for the next peak – use the </para>
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<para><command>> tasub calcang qh qk ql ei ef </command></para>
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<para>command to see the relative values of S1 and S2 as calculated from the lattice
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parameters!</para>
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<para>
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</para>
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<para>Repeat for at least one other peak, preferably one orthogonal to the first. </para>
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<para><command>> tasub addref 0 0 1 </command></para>
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<para><command>> tasub listref </command> (to see the observed peaks in your list
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(e.g. number 4 and 5)) </para>
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<para><command>> tasub makeub 4 5 </command>(this used peaks 4 and 5 to calculate the
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UB matrix) </para>
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<para><command>> tasub update </command></para>
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<para><command>> tasub listub </command></para>
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<para>Once this has been set, then you should be able to drive your spectrometer to any
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accessible qh, qk, ql and en.</para>
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<warning>
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<title>
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</title>
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<para>At the end of each change, be sure to type <command>> tasub
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update</command></para>
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</warning>
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</example>
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</sect1>
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<sect1>
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<title>Reducing background with a slit scan</title>
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<para>Once your sample has been aligned, add the PG filter to the instrument. You could test
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the effectiveness of the filter by scanning a peak that will display higher order
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scattering – e.g. (½ 0 0) which does not exist except from higher order scattering from
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the (1 0 0 ). Sometimes you might want to add an additional filter. Finally you can scan
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your slits to reduce the background scattering. </para>
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<para><command>> runscan pa_left -15 -2 27 time 1 </command>(scans 27 points, for a time
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of 1 seconds per point)</para>
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<para> After this, consider if you need to add more shielding to the detector drum or any
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other part of the instrument (e.g. manual slits on analyser arm, additional PG
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filters).</para>
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</sect1>
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<sect1>
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<title>Setting the (new) lattice parameters</title>
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<para>During your experiment you may need to change the lattice parameters (due to a phase
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transition, thermal expansion etc). If this is the case you MUST find and optimise two
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new reflections to make your UB-matrix from. For example, scan a Qh peak as follows: </para>
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<para><command>> drive qh 4 qk 0 ql 0 en 0 </command></para>
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<para><command>> runscan qh 3.985 4.015 31 time 5 </command></para>
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<para>The centre of this scan should be close to 4, but could be shifted. This will be the
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fit value from the scan. Then you can <emphasis role="underline">change the <emphasis
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role="bold">a</emphasis> lattice parameter</emphasis> accordingly in tasub </para>
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<para>
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a<subscript>new</subscript>=a<subscript>old</subscript>(peak<subscript>calculated</subscript>/peak<subscript>centre
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from scan</subscript>) </para>
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<para><inlineequation>
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<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
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<mml:mrow>
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<mml:msub>
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<mml:mrow>
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<mml:mi>a</mml:mi>
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</mml:mrow>
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<mml:mrow>
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<mml:mi>n</mml:mi>
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<mml:mi>e</mml:mi>
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<mml:mi>w</mml:mi>
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</mml:mrow>
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</mml:msub>
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<mml:mo>=</mml:mo>
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<mml:msub>
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<mml:mrow>
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<mml:mi>a</mml:mi>
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</mml:mrow>
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<mml:mrow>
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<mml:mi>old</mml:mi>
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</mml:mrow>
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</mml:msub>
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<mml:mrow>
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<mml:mo>(</mml:mo>
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<mml:mfrac>
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<mml:mrow>
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<mml:mo>⁢</mml:mo>
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<mml:msub>
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<mml:mrow>
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<mml:mi>peak</mml:mi>
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</mml:mrow>
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<mml:mrow>
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<mml:mi>calculated</mml:mi>
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</mml:mrow>
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</mml:msub>
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</mml:mrow>
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<mml:mrow>
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<mml:msub>
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<mml:mrow>
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<mml:mi>peak</mml:mi>
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</mml:mrow>
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<mml:mrow>
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<mml:mi>centre from scan</mml:mi>
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</mml:mrow>
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</mml:msub>
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</mml:mrow>
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</mml:mfrac>
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<mml:mo>)</mml:mo>
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</mml:mrow>
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</mml:mrow>
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</mml:math>
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</inlineequation></para>
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<para><command>> tasub cell a b c alpha beta gamma </command></para>
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<para>The next peak can be aligned in the same way </para>
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<para><command>> drive qh 0 qk 4 ql 0 en 0 </command></para>
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<para><command>> runscan qk 3.985 4.015 31 time 5 </command></para>
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<para>Once you have changed your unit cell parameters, you need to add the two new peaks
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into your reference list, optimise the goniometers again and re-make your UB matrix with
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these new peaks</para>
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<para><command>> tasub cell</command></para>
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<para>3 9 15 90 90 90</para>
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<para><command>> tasub cell 2.9 8.7 14.5 90 90 90</command></para>
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<para><command>> tasub addauxref 0 0 4 </command></para>
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<para><command>> tasub addauxref 0 4 0</command></para>
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<literallayout>
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NO QH QK QL S1 S2 SGU SGL EI EF
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1 0.00 0.00 4.00 22.62 -27.10 0.00 0.00 25.86 14.87 (old lattice parameters)
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2 0.00 4.00 0.00 -65.74 -51.21 0.00 0.00 25.86 14.87 (old lattice parameters)
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3 0.00 0.00 4.00 -156.85 -28.38 0.00 0.00 25.86 14.87 (new lattice parameters)
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4 0.00 4.00 0.00 -66.10 -53.30 0.00 0.00 25.86 14.87 (new lattice parameters)
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</literallayout>
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<para>You can see already that by changing the lattice parameters the scattering angles
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change. So you need to optimise these peaks again, as before and add the new reflections
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to the list before re-making your UB-matrix.</para>
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<para>If your sample is cubic (and remains cubic at low temperatures) and you are in the HK0
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scattering plane, then the lattice parameters are best set with a peak that involved
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both H and K – for instance the 110 peak.</para>
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<para>Make sure after you have changed your lattice parameters, and both peaks have been
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added to the reference list that you remake your ub matrix! </para>
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</sect1>
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</chapter>
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