Aligning the sample in the beam can be easily achieved using the precision movements of the sample tables.
Both the base table (base) and the precision translation stage (pxy) can be operated through the GDA interface. The precision translation stage has a 0-100mm translation in x and y (z is the beam direction). The base table motors can also be moved to give access to further translation, or can be used if the sample environment is too big or too heavy (greater than 1kg) for PXY. Ask a beamline scientist about the limits of this table in your set up.
Each table has two motors that give precision movement in either the x or y direction. The names of these motors are "base_x" and "base_y" for the base table and "pxy_x" and "pxy_y" for the precision stage.
Most fine positioning throughout the experiment can be achieved using two basic commands; "pos" to position the motor to a defined position (an absolute move) and "inc" to incrementally move the motor by a set distance.
The syntax is as follows, for pos
> pos nameofmotor position
On the sample platform an example of this would be
pos pxy_y 10.3
and for inc
> inc nameofmotor distance
An example of this might be when you are moving between two know capillary locations on a holder using the base table
inc base_x 9
For the X directions a positive move moves the motor outboard or away from the storage ring and a negative one towards storage ring.
For the Y direction a positive move moves the motor to drive the sample vertically upwards with negative being down.
To position samples in the beam, often a horizontal (or vertical) scan can be faster and more helpful than incremental steps. This is achieved by moving, for example, the precision stage in small increments and monitoring the reading on one of the the beamstop diodes named e.g. "bs3diode".
To scan across the sample:
>scan nameofmotor startposition endposition increment nameofdetector
> scan pxy_x 5 15 0.1 bs3diode
An alternative scan if you do not necessarily want to loose your starting position is rscan. This carries out a relative scan about the location the motor is in currently
> rscan nameofmotor relativestartposition relativestopposition increment nameofdetector
> rscan pxy_y -5 +5 1 bs3diode
So if you were at pxyy 15 this scan would start at 10 and go to 20 in steps of one.
A feature on I22 is that after each scan, and if the scan makes it possible, GDA will calculate a peak position and an edge position which can then be moved to by
> go peak
> go edge
These are useful during setting up and alignment of samples.
It should be noted that GDA will report an error message if these calculations cannot be carried out on the data from a scan, e.g. if you are carrying out an experiment using ncddetectors in a scan command. As ncddetectors has image data only the underlying code cannot calculate peak of edge positions.
If in doubt, ask!
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