DACs: Sample mounting, centering and collection

1. Sample mounting

1. Open the High Pressure tab on the MX1 Controls program.

2. Open the hutch, click Move to move the goniometer to the DAC mount position, with Omega at 135 degrees.

3. Put the DAC on the goni with the alignment pins facing down, and made sure it is completely flat with the mini spirit level. It is very important that it is flat, otherwise it will be very difficult to center. Adjust the DAC by rotating it on its magnetic mount. Do not bump the beamstop or the goniometer.

4. Close up the hutch and move Omega to 45 degrees.

2. Sample centering

1. Roughly center the opening onto the cross hairs. If you can’t find the opening, click “link to camera full view” on the DAC GUI to see a larger view of the camera facing the DAC.

2. Adjust Sample X and Sample Y until the sample comes into focus. Will be movement of ~500 um. Note down the Sample X and Sample Y position, or enter it in the "Focus at Omega = 45" boxes on the GUI

3. Rotate by 180 degrees to Omega = 225 and adjust Sample X and Sample Y until the sample comes into focus. Note down Sample X and Sample Y position or enter it in "Focus at Omega = 225" box on the GUI.

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

5. Adjust the focus of the camera via the DAC centering GUI. It will be a value somewhere around 10000. The focus should be adjusted until the sample is in focus at 45 and 225 degrees.

6. If the sample does not stay centered in the X axis between 45 and 225 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

Click the Screen button on the High Pressure tab, this will autofill information in the data collect tab. Adjust attenuation or sample exposure time as necessary in data collection. 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. When you are happy with your settings, click Copy and the screening options will be copied to the dataset tab.

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. 

The gonimeter and data collection information will be autofilled by clicking the relevant buttons in the High Pressure tab.

After runs 2 and 4, when you change kappa or phi, you will need to 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. But make sure that the sample is in focus with Omega at 45 and 225 degrees.

After data collection, click the Move button to return the gonimeter to a safe position for dismounting your DAC.