Mini-Kappa - MX1

Owned by MX Cluster (Unlicensed)
Last updated: Jul 27, 2024 by AS MX Wiki
3 min read

Introduction

The mini-kappa allows off-axis orientations of a crystal to be collected, yielding greater coverage and redundancy which is very important for low symmetry space groups.

 

The addition of the mini-kappa introduces two new axes of rotation (KAPPA and PHI). These allow the crystal to be reoriented before an OMEGA collection, and this where it may get a touch confusing. Read on for help!

Controlling the Mini-Kappa

The mini-kappa controls are accessed through MX1 User Controls GUI:

 

mini kappa.png

 

‘Simple’ strategy for collection

We can use a very simple and direct strategy to get a full sphere of data without causing data to be obscured by the mini-kappa shadow.

Run

omega (ω)

kappa (κ)

phi (φ)

1

1 - 360

0

0

2

180-360

180

0

3

180-360

180

90

How do I collect my data?

  1. Center your crystal as normal with phi and kappa both set to zero. (See for sample interface)

  2. Take screening collections of the crystal to judge the attenuation needed for good resolution but with no overloads. The unit cell for each screening collection will be determined through the auto-collection process and displayed on the processing interface. This should give you an indication if your crystal system is low symmetry and you will get an idea of the need to collect further data. It Is better to have more multiplicity of reflections than incomplete data. ( )

  3. Run 1: Click the Run 1 button. This will populate the dataset tab with the correct goniometer settings for a 360 degree collection. Make sure your file prefix is correct. Then click Dataset and wait.

  4. After Run 1 has finished, center the top of the steel pin in the crosshair and move Omega to 0 by clicking Omega to Zero button. All movements of the kappa motor must be carried out with Omega at zero.

  5. Click Run 2 button, this will move the mini-kappa and populate the Dataset tab with the correct settings.

  6. Re-center crystal, at this point your sample pin is no longer in line with the cryo gas and will warm, this may mean you see some thermal expansion making centering the crystal tricky.

  7. Start Run 2 by clicking Dataset in collection GUI.

  8. After Run 2 has finished, click the Omega to Zero button, then Run 3 button.

  9. Re-center crystal between 180 - 360°

  10. Collect Run 3 by clicking Dataset in collection GUI.

  11. After Run 3 has finished, center the top of the steel pin in the crosshair and click Return to Normal.

How do I process my data?

See the write-up here. 

Common Problems

It is possible that in the kappa or phi rotations, the crystal may pass outside the cryo cooling gas – keep an eye out for this and tell the beamline scientists if this will be a problem for you.

 

It is possible that the autoprocess might index a different P1 lattice in the three runs, This is unlikely but could happen. To check your lattice dimensions, open a terminal and type the following commands:

cd (yourexperiment_merge)

grep UNIT_CELL_CONSTANTS run(your run number)

and you will be able to see if the lattice is the same.