sics/site_ansto/manual/dbSICSch15_beamstop.xml

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<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink"
    version="5.0">
    <info><title>Beamstops</title><author>
            <personname>Ferdi Franceschini</personname>
        </author>
        <date>2008-12-15 </date>
    </info>
    <sect1>
        <title>Commands</title>
        <para>Raising and lowering of beamstops is implemented via the <command>selbs</command> 
            command.</para>
        <para><command>selbs</command> raises the selected beamstop in a safe manner. It will leave
            the previously selected beamstop in place until the selected stop is fully raised and
            then lower the other beamstop. </para>
        <para><emphasis>If you are changing the <option>x z </option>coordinates there is no safe
                sequence. You should set maximum attenuation or close the fast shutter before moving
                the beamstops.</emphasis></para>
        <para>You can monitor the beamstop position via GumTree as it is being raised, and you can
            also see the state by reading angles. </para>
        <para>The odd and even numbered beamstops are on separate parallel axes which are
            horizontally offset by about 10cm. This means that beamstops must be raised to an angle
            which is a few degrees of vertical so that the odd and even beamstops will overlap, you
            will see that the odd numbered stops will be at roughly 93 degrees and the even numbered
            ones will be at 86 degrees to vertical when raised.</para>
        <variablelist>
            <varlistentry>
                <term><command>selbs </command><replaceable>n </replaceable><replaceable>x
                    z</replaceable></term>
                <listitem>
                    <para>Allowed <replaceable>n</replaceable>
                        <option>1,2,3,4,5,6</option> where </para>
                    <para>1 = largest beamstop </para>
                    <para>6 = smallest beamstop</para>
                    <para><option>x</option> = beam x position in detector coordinates</para>
                    <para><option>z</option> = beam z position in detector coordinates</para>
                    <para>The beam position (x,z) is optional</para>
                    <note>
                        <para>This is a blocking command. You will not be able to run other commands
                            in the session running <command>selbs</command> until it has
                        finished.</para>
                    </note>
                </listitem>
            </varlistentry>
        </variablelist>
        <example>
            <title>selbs example</title>
            <para><command>selbs 1 487.7 490</command></para>
            <para>Select beamstop one and position it over the middle of the detector.</para>
            <para><command>selbs 2</command></para>
            <para>Leave the beamstop carriage in place and select beamstop two.</para>
        </example>
    </sect1>
    <sect1>
        <title>Parameters</title>
        <variablelist>
            <varlistentry>
                <term><varname>beamstop</varname></term>
                <listitem>
                    <para><command>selbs</command> also sets a variable called
                        <varname>beamstop</varname> and saves it in the data file.</para>
                    <para>Possible values for <varname>beamstop</varname></para>
                    <para><option>0</option>
                        <command>selbs</command> has never been run or the sics status.tcl file has
                        been cleared</para>
                    <para><option>-1</option>
                        <command>selbs</command> failed while driving the beamstops</para>
                    <para><replaceable>n</replaceable>
                        <command>selbs</command> completed driving successfully and has selected
                        beamstop <replaceable>n</replaceable></para>
                    <para>The value of the "beamstop" variable persists between restarts of SICS.</para>
                    <warning>
                        <para>If someone drives the beamstops directly then the
                            <varname>beamstop</varname> variable may be wrong</para>
                    </warning>
                </listitem>
            </varlistentry>
        </variablelist>
    </sect1>
    <sect1>
        <title>Troubleshooting</title>
        <para>Beamstop position can be checked visually (by eyes) from the vessel port with touch. 
            To do this,  you should drive the detector to position 9300mm, and view from the middle
            vessel port.</para>
    </sect1>
</chapter>