Multi-axis goniometer (SmarGon)

Multi-axis goniometers allow re-orientation of crystals to improve data quality. The use of such devices is particularly useful for:

• smart data collection strategies (better completeness of data especially for low-symmetry spacegroups)
• reduced radiation damage by using smaller overall oscillation range
• optimised anomalous data collection (Bijvoet pairs collected on the same frame)
• improved high-multiplicity SAD data collection protocols
• comparing crystals in the same orientation
• multiple crystal data collection (collect only what has not been collected before)
• help in point group determination
• reducing/avoiding spot overlap (better spot separation)

The SmarGon 5D goniometer is mounted on the main omega rotation axis. The SmarGon 5D head contains the x, y, z translation stages that are used for sample centring and translation, e.g. in grid or line scans. The chi angle is generated by the differential translation of two horizontal axes (x1, x2). The device has chi range between 0 - 90 deg but for operational reasons this is restricted to 0 - 45 deg. The phi axis is mounted on top of the chi axis and has a range of 0 - 360 deg.

Screening a crystal, i.e. collecting three reference images 45 deg apart in omega will trigger two pipeline to calculate crystal orientations:

1. dials.align_crystal, based on dials.indexing
2. XOalign, based on mosflm indexing

Only crystal orientations that can be achieved will be displayed in Synchweb.

These crystal orientations can be imported directly via the GDA 'Strategies' button in the Data Collection tab.

In the GDA client chi and phi values can be entered either in the data collection table:

or in the data collection form.

If a value is changed in the table the form will be updated automatically and vice versa. Values can be entered within the allowed range, chi: 0-45 deg, phi: 0-360 deg.

The GDA align tab contains buttons and edit fields for the chi and phi as well as for the omega axis. Keep in mind that the main rotation axis is omega.

When a new sample is loaded the Keyence and OAV autocentring are run, then chi and phi are moved to 0 deg. If chi/phi values which are different from 0 deg are requested in the data collection table, then a centring request pop-up window will appear and the user has to centre the sample in the sample alignment tab. This step is required because of the mechanical properties of the goniometer which causes the sample to move away from the crosshair if chi and/or phi are moved.

Once the user has confirmed that sample centring is complete by clicking the button, the data collection will continue.