DACs: Sample mounting, centering and collection

1. Sample mounting

1. Open the hutch, move Omega to 90 degrees.

2. Put the DAC on the goni with the alignment pins facing down, and made sure it is completely flat with the mini spirit level. 

3. Close up the hutch and move Omega to 0 degrees.

2. Sample centering

1. Roughly center the opening onto the cross hairs.

2. Open the DAC centering tab of the QEGui

3. Adjust Sample X until the sample comes into focus. Will be movement of ~500 um. Note down the Sample X position, or enter it in the "Focus at Omega = 0" box on the GUI

4. Rotate by 180 degrees to Omega = 180 and adjust Sample X until the sample comes into focus. Note down Sample X position or enter it in "Focus at Omega = 180" box on the GUI.

5. Split the different between the Sample X positions (should be shown in the GUI) and change it to this position. This will be the position you need for collections. 

6. Adjust the focus of the camera via the DAC centering GUI. It will be a value somewhere around 14700 - 14800. The focus should be adjusted until the sample is in focus at 0 and 180 degrees.

7. If the sample does not stay centered in the X axis between 0 and 180 degrees, it is likely because the diamonds are slightly misaligned. If it does not stay centered on the Y axis, it may be because the cell is not perfectly perpendicular to the beam direction. It is a good idea to reset the camera focus, and repeat the sample mounting and then centering. 

3. Screening

If starting at 0 degrees, do a 20 degree wedge starting at -10 degrees. Adjust attenuation or sample exposure time as necessary to get enough data. There will be significant shadow from the cell, rings from the gasket, and diffraction spots from the diamonds. You don't want any overloads apart from diamond reflections. If there are overloads, you need to decrease exposure time or increase attenuation. It will help to scroll through the frames on ADXV to check when overloads are coming up. 

4. Data collection 

For maximum completeness and redundancy (and because each run doesn't take long), it is a good idea to collect as much data as possible. 

After runs 2 and 4, when you change kappa or phi, set the focus back to its original value, and repeat the Sample centering steps. Although you probably will not need to change the camera focus. If you leave the camera focus at the same value, the adjustment of Sample X will be much smaller.