Alignment of the KappaCCD2000 on an FR591 rotating anode generator.
The alignment of the KappaCCD2000 on an FR591 rotating anode uses an alignment stage. This alignment
stage is designed to make uncoupled translations and rotations of the diffractometer, to make the
alignment of the diffractometer a fast converging process.
Alignment of the goniometer consists of two translations and two rotations perpendicular to the
beam, one up and one horizontal, parallel to the table. The translation up is done with two height
adjustments at the side of the goniometer. The rotation up is done with a single height adjustment
at the end of the goniometer, below the theta arm.
The two horizontal motions (rotation & translation) are done with two micrometers, which we call
Micrometer #1 and #2. These micrometers move the goniometer relative to a metal bar, which must be
firmly fixed to the generator tabletop before using the micrometers. During the use of the
micrometers, the hover pads must be activated.
There are two versions of the alignment plate. In the first version, the hover support positions
and the diffractometer feet positions, do not coincide. Here the micrometers are positioned at two
different sides of the goniometer. This is shown in the pictures below.
In the second version of the alignment table, the hover support positions and the diffractometer feet
positions coincide. Also the micrometers are positioned adjacent to one another at the back of the
goniometer. This is shown in the drawing below:
The alignment procedure of the goniometer assumes that the collimator is optimally aligned and
points at the centre of the goniometer. When we are sure of this, we take the following steps:
- Alignment of the multilayer graded mirror and maximization of the beam intensity.
- Centering of the X-ray beam with respect to the mirror exit port
- Translation of the goniometer such that the direct beam shoots through the collimator.
- Rotation of the goniometer such that the direct beam shoots through the crystal position
Alignment of the multilayer graded mirror is done using a
Xyclops X-ray imager.
 |
This small camera can be connected to the multilayer graded mirror housing using a
Xyclops adapter. The Xyclops and the mirror adapter are essential to make sure the
X-ray beam shoots through the center of the mirror output port. This is crucial for
getting an optimum intensity and alignment of the goniometer. |
To make sure the beam is centered we use two alignment collimators:
One is completely open and is called the open-beam pipe. The other one is screened with a half-moon at the entrance. This is called the
half-beam pipe. The orientation of the half moon is indicated with dots at the outside of the collimator.
| o facing up |
Half moon up |
| oo facing up |
Half moon left |
| ooo facing up |
Half moon down |
| oooo facing up |
Half moon right |
The alignment collimators are always used to look at the primary beam falling on the detector and
therefore they should always be used at relatively low power (45kV, 35mA) together with the
absorber.
For centering the beam at the crystal position, a 1.5 mm bar on a goniometer is used.
When properly centered, this should absorb the beam half-way; hence it is called the half-beam absorber.
This 1.5 mm bar must be aligned using the video microscope and the crystal alignment routine on the server PC. Use position /
(former view 1)and use the button Rotate 180°: the edge of the bar must be in the centre (it must absorb half of the beam). But it is better to leave a gap
then to have overlap between the two positions.
You are advised to keep the half-beam absorber aligned on a goniometer head for future alignments.
- When adjusting the goniometer up or down, make sure none of the hovers is activated.
- When adjusting the goniometer horizontally, make sure ALL hovers are activated.
- The hovers must slide very smoothly; if not, the sensitive alignment will not work right.
- Remove the mirror output port and place the Xyclops on the adaptation port. Be careful! There is no X-ray safety
(yet), so when the Xyclops is removed you will have an open X-ray beam. So be very careful when opening the shutter
and always use a second beamstop behind the goniometer.
- Set the generator power to 45 kV 35mA.
- Set the generator shutter to GCU disable on the FR591 panel and open the shutter with the FR591 panel. Do not use
the goniometer PC, as this may sometimes cause the shutter to open by accident.
- Adjust the mirror rotations until you have found the primary beam.
- Adjust the horizontal and vertical shift of the mirrors, (concurrently with the mirror rotations to remain maximum
intensity) until the primary beam is roughly cut in half at the right end of the monitor.
- Align the mirror with the rotations. First one rotation to get a single reflection and then with the second until
the doubly diffracted beam is at maximum intensity.
- Mark the centre of the mirror output port as follows:
- Mark the position of the doubly diffracted beam.
- Rotate the Xyclops 180 degrees around the X-ray beam and mark the beam again.
- Draw a line between the two marks and mark the centre. This is the centre of the mirror output port.
- Shift the doubly reflected beam as good as you can to the centre mark on the monitor (in steps with the vertical and
horizontal adjustment of the mirror and with rotational adjustments to keep it at maximum).
- Close the shutter and remove the shutter safety keys.
- Remove the Xyclops and mount the mirror output port.
- Put on the X-ray absorber on the mirror output port of the multilayer graded mirror.
- Connect the vacuum or helium the mirror housing and switch it on.
- Hoover the goniometer such that the direct beam shoots (as can be judged visually) past the shutter block and hits
the detector.
- Set the generator shutter to GCU disable on the FR591 panel
- Set the detector to "binned" mode.
- Make 100x, 1 second measurements and make a large statistics block around the beam. The position of the beam is now
continuously displayed.
- Adjust the backside vertical adjustment until the reflection is roughly at line 650.
To get close to the position where the goniometer is more or less at the same height as the direct beam we use a tool
which is put on the collimator and which, if the goniometer is at the right height, blocks the direct beam in half. This is
the "half absorber yoke".
- Put the half absorber yoke on the collimator holder and adjust the two front vertical adjustments (both the same
amount) until the intensity is about half (30-70%) the open beam.
- Close the shutter and remove the shutter safety keys.
- Remove the X-ray absorber off the mirror output port of the multilayer graded mirror.
- Hover the goniometer in front of the mirror output port.
- Place the open beam pipe and put the absorber on the tip of the pipe.
- Measure the intensity of the X-ray beam on the server PC using Setup/Calibration/ Continuous measurements of 0.2s.
- Hoover the goniometer (rotated/shift) slowly until the beam is visible. Take care the goniometer is parallel to the
mirror output port. When the beam is found slight rotate until the reflection is horizontally in the middle of the bitmap
and shift the front of the goniometer (the shutter) horizontally until maximum intensity.
- Mount the fixing bar at the table with screws and fix the alignment plate to the fixing bar.
At this point you can see the direct beam through the largest collimator available (the open beam pipe). From here on we go
to the fine alignment, which is also where you would normally start after changing a filament.
Before starting on this section makes sure that:
- The microscope is well aligned
- The mirror is reasonably well aligned and shoots through the center of the mirror output port.
- The goniometer is roughly aligned and the primary beam is visible when making an exposure using the open beam pipe with the attenuator.
- The micrometers are set to a value of about 20.
- The fixing bar of the alignment plates is screwed to the table.
Take care:
When changing the open beam pipe, always make sure the shutter is closed by checking the shutter open lamp!
Initial run:
- Place the open beam pipe with absorber.
- Set the detector to "unbinned" mode.
- Measure with setup/beam alignment with 1 second exposures.
- Place the half-beam pipe with absorber.
- Measure the vertical position in both positions (o and o o o) and use the position with lowest intensity
- Adjust with front-vertical side screws (both the same amount) until you're at about 50% of the sum of the two intensities
- Measure the horizontal position in both positions (o o and o o o o) and use the position with lowest intensity
- Activate the hovers and adjust horizontally with micrometer #2 until you're at about 50% of the sum of the two intensities
- Deactivate the hovers.
- Measure with the open hole with absorber. If the intensity is much higher then before, repeat the above.
- Mount a goniometer head with pre-aligned half-beam absorber (1.5 mm bar).
- Start a measurement vertical. Two measurements are executed with Phi 180° rotated and the difference between the two measurements.
- Adjust with the backside vertical adjustment (Rotation vertical) to the proposed "new" value (with measurement Continuous)
- Redo the vertical measurement until both measurements are equal within 10%.
- Start a measurement horizontal. Two measurements are executed with Phi 180° rotated and the difference between the two measurements.
- Activate the hovers.
- Adjust with micrometer #1 (Rotation horizontal) to the proposed "new" value (with measurement Continuous)
- Redo the horizontal measurement until both measurements are equal within 10%.
- Deactivate the hovers.
- Put in the open beam pipe and absorber and carefully adjust the mirror rotations until maximum intensity (don't lean on the rotating anode tube!)
- Repeat the first alignment procedure, but now more accurately.
- The difference between the two horizontal measurements with the half beam pipe should be less then 20%.
- The difference between the two horizontal measurements with the half beam absorber bar on the goniometer head should be less then 10%.
- Place the 373 collimator with absorber and repeat the measurements using the half beam absorber bar on the goniometer head.
For normal measurements there are three standard collimators.
 |
Put in the largest (normal measurement) collimator with the attenuator and measure the intensity under similar
circumstances used previously. Do the same with the other collimators. Write these values down for future reference. |
This finishes the fine alignment of the goniometer.
- Close the shutter and set the shutter safety key to "closed".
- Hoover the goniometer back and sideward in the slits of the alignment plate.
- Switch off helium or vacuum
- Dismount the mirror output port and mount the Xyclops adapter.
- Mount the Xyclops.
- Set the shutter safety key to open and open the shutter
- Adjust the mirror rotations until the primary non-reflected beam is visible.
- Dismount the mirror and be sure you don't change the adjustments
- Turn off the X-rays
- If the mirror is not adjusted to the direct beam before dismounting the mirror adjust the small input and output apertures
visually in the middle. First adjust the input apertures with the two rotations, and then adjust the output aperture with the
horizontal/vertical adjustment. The input Be window holder must be dismantled for this.
- Mount the mirror on the mirror support. During fastening of the screws (rigid) press the mirror housing slightly to the front in the direction of the HV cable.
- Turn off the X-rays
- Make sure the fixing bar for the goniometer alignment is not yet fixed to the table.
- Set the micrometers to 20
- Set the goniometer to table distance with all vertical adjustments to 10 mm (one full rotation = 1 mm)
- If the mirror is not adjusted to the direct beam before dismounting the mirror adjust the small input and output apertures visually in the middle. First adjust
the input apertures with the two rotations, and then adjust the output aperture with the horizontal/vertical adjustment. The input Be window holder must be dismantled for this.
- Mount the mirror with height adjustment plates until it is approximate horizontal (typically one adjustment plate is needed).
- During (rigid) fastening of the screws press the mirror house slightly to the front (in the direction of the HV cable).
- Hover the goniometer until it is close to the mirror output port and adjust the two front vertical adjustments (both the same amount) until the input port of the goniometer
is visually at the same height as the mirror output port.
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Last change 15 March 2002
