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7. Alignement of the 6ID-D Side Station monochromator

In this chapter the general procedure to align the 6ID-D Side Station from scratch is described. In this chapter only procedures affecting equipment of the 6ID-D Side Station are described. Before any work is done on the side station it should be assured that the 6ID-B Main Station and its equipment, exspecially the white beam slits and the monochromator are aligned properly. Warning! All alignement procedures described in this chapter should only be executed by staff personal from Forschungszentrum Jülich or $ \mu$-CAT, which has been trained to do so. This chapter is not intended for beamline guests. Whenever this text refers to white beam mask or filters the respective equipment of the 6ID-D Side Station is meant and not of the 6ID-B Main Station.

In general the alignement of the 6ID-D Side Station should be performed in same order like it is described in this text. Nevertheless a complete realignement of the beamline might not be necessary in all cases.

Exspecially the alignement of the white beam mask (section 7.1) and the filters (section 7.2) is critical. Any misalignement of those two components can lead to a water leak inside the UHV-vacuum of the windowless main beamline which has to be avoided under any circumstances.


7.1 Alignement of the white beam mask

The first steps in the alignement process of the 6ID-D Side Station are done optically with the fluorescence sreen of the 6ID-B Main Station mounted directly in front of the white beam stop of the 6ID-B Main Station. To make sure that no beamline components are destroyed and the fluorescence sreen is not burned by the white beam the undulator gap has to be opened to at least 40 mm so that only a few Watt of power are produced. As a saftey precausion ask the flour coordinator to set the lower limit of the undulator gap to 40 mm. That way the undulator can not be closed by accident causing serious damage to the beamline.

Next put in the white beam stop in front of the white beam mask. Remove the spacers before putting in the screen controlled by the 6ID-B Main Station computer. The spacers normally prevent the fluorescence screen from being hit by the white beam. The camera looking at the fluorescence sreen has to be realigned because it normally looks at the monochromatic beam of the 6ID-B Main Station, which is 25 mm above the white beam.

Now try to get the white beam through the white beam mask. The filters and the monochromator should be at a position where they do not obstruct the beam (see tables 7.1 and 7.2).

To align the white beam mask the whole first monochromator chamber can be moved horizontally and vertically with the two motors m1_x and m1_y, respectively. The aperture of the entrance side of the white beam mask is 10×20 mm2 (vertically × horizontally), the beam is reduced to a maximal size of 2×4 mm2. The mask should be aligned optically with the help of the above mentioned fluorescence screen. Warning! On the downstream side of the first monochromator chamber is a stand for the beam pipe. This beampipe is directly attached to the first monochromator chamber, therefore the stand has to be disconnected from the beam pipe before the m1_x or m1_y motors are moved. To avoid unwanted movements of those motores the motor drivers are normally switched of. After alignement of the motors you should connect the stand to the beampipe and switch of the motor drivers again.


7.2 Alignement of the filters


Table 7.1: Position of the water cooled filters in front of the monochromator (filter). There are 5 filter positions, 1 empty, 2 aluminium filter and 2 aluminium copper combinations, seperated by 1 mm. There is an additional hole, where the beam can pass through. The positions in the last line are from the survey done by Peter Hiller in October 2000.
Position F5 F4 F3 F2 F1 Hole
Filter empty AlCu AlCu Al Al  
Oct 2000 86.85 68.85 50.85 32.85 14.85 -4.0


The first filter, a 1 mm carbon foil is directly attached to the white beam masked and permanently in the beam. In addition either a 1 mm aluminium filter or a combined 1 mm aluminium +1 mm copper filter can be moved into the white beam with a filter changer (filter). To align the filter horizontally the undulator gap should be open as described in 7.1. The horizontal alignement is done optically with the motor filter. The filter is not correctly aligned if any round shapes of the beam are observed on the fluorescence screen. The beam has a squared size after the white beam mask, assuming, that the beam profile is defined by the white beam mask. This is the case if the white beam slits in front of the Kohzo monochromator are wide open. Try to center the filter horizontally. If there is any cut off observed vertically the filters are not mounted at the correct hight with respect to the white beam mask. Warning! Do not proceed. Ask Peter Hiller or Thomas Brückel for advice.

Warning! Under no circumstances should the filter be exposed to the white beam with closed undulator gap if not all filter positions have been aligned correctly and one of the five filter positions is in the beam position. This might lead to serious damage to the beamline and a water leak inside the UHV vacuum. It is strongly recommended that the equipment protection system (EPS) (see chapter 8) is tested after each realignement of the filters.

Warning! Under no circumstances should the first monochromator crystal exposed to the white beam with closed undulator gap if there is no aluminium or aluminium-copper filter in the beam. This might lead to serious damage to the beamline and a water leak inside the UHV vacuum.


7.3 Alignement of the first monochromator crystal


Table 7.2: Positions of the crystals of the first monochromator (m1_xtal). The maximum of 3 monochromator crystals is implemented. The positions in next last line are from the survey done by Peter Hiller in October 2000. The positions in the last line are from the alignement with the x-ray beam from march 2001. To move the first monochromator crystal out of the white beam move 10 mm in positive direction, for example if the (331) crystal is in the beam go to position 65.6.
Position 1 2 3
Crystal (311) (111) (331)
October 2000 150.90 102.70 55.305
March 2001 150.65 102.55 55.6


Once the white beam mask and the filters are aligned the $ \vartheta$-angle and the position of the first monochromator crystals can be aligned. Warning! This procedure has to be done with opened undulator gap. To do so the first monochromator crystal is driven into the beam using motor m1_xtal until roughly halfe of the white beam is cut off. Than motor monu is used until the crystal is parallel to the beam. The crystal is parallel to the beam when a rotation in positive as well as in negative direction leads to a larger cut off of the white beam seen on the fluorescence screen.

In the next step the horizontal position of the first monochromator crystal has to be aligned. To do this use motor m1_xtal to determine the position where the first monochromator cuts off the complete white beam and the position where the whole white beam can pass the crystal. The mean of these two positions gives you the position where the crystal is aligned in the center of the white beam.

This procedure has to be repeated for all three monochromator crystals. When this is finished the fluorescence sreen has to be pulled out of the beam and the spacers have to be put back into place so that the white beam cannot hit the fluorescence sreen any more. In addition the camera has to be realigned to look at the monochromatic beam of the 6ID-B Main Station, the position is 25 mm above the white beam.

The alignement procedures requiring an opened undulator gap are finished, the 6ID-D Side Station is now able to withstand the full heatload of the undulator. All the following steps should be executed for one of the three monochromator crystal pairs. Once one crystal pair is fully aligned the procedure should be repeated two times for the other two monochromator crystal pairs.

To proceed close the undulator gap to a value around 15 mm to 20 mm. The next task is to find the reflected beam from the first monochromator on the fluorescence screen behind the second monochromator. This fluorescence screen is operated through the small TV-system positioned close to the beamline computer. The fluorescence screen can be moved in controlled by an electro magnet. The camera is only operating while the corresponding switch on the TV-system is manually hold down. This is necessary, because the cameras cooling system is not sufficient in vacuum so the camera can only be operated for short time periods.

Move the second monochromator crystal to a position, where it is not in the beam (see table 7.3 and rotate it so that it is parallel to the beam, that means move motor monu to $ \vartheta$. You should position the second monochromator chamber (motor montrav) somewhere in the middle of the railsystem, I usually used the value -2239.54. Use the command mono_calc_position to calculate the position of the motors monu, mond and montrav.

Now the reflected beam from the first monochromator has to be found. The fluorescence screen behind the second monochromator has to be put in and the camera switched on. Look for the beam a few degrees around the calculated $ \vartheta$ angle of the first monochromator. If no beam is found, the chi angle of the first monochromator (motor m1_chi) has to be changed in 0.5 degree steps and the search has to be repeated. Once the beam from the first monochromator crystal has been found align with the motors monu and m1_chi that it is easily visible in the middle in the fluorescence screen.

The next step is to align the $ \vartheta$ angle of the second monochromator crystal. Move motor m2_xtal until roughly half of the beam is cut of by the second monochromator crystal. This position is of by several millimeters from the positions given in table 7.3, because the beam from the first monochromator crystal is not in the correct position right now, this will be done later. Now align $ \vartheta$ rotation of the second crystal in the same way as described in section 7.3 for the first monochromator crystal. But the aligned value now corresponds to two times your calculated $ \vartheta$ value.

Now a precise alignement of the motor m1_chi has to be done. Move the beam up with this motor until you see a sharp edge in the beam profile which is still cut off by one half from the second monochromator. Move m1_chi until this sharp edge is in the middle of the beam. This sharp edge belongs to the crystal holder of the second monochromator crystal and gives you the upper and lower end of the 5 mm wide crystal. Now move the beam down and repeat the procedure. After both positions have been determined move the beam to the mean of the two positions, this is the final position for m1_chi.

Finally $ \vartheta$ of the first monochromator crystal has to be aligned. For that reason align the second monochromator crystal (motor m2_xtal) that it cuts of exactly half of the beam. Now move the beam with motor monu a few hundrets of a degree that way that it is still fully visible on the fluorescence screen and align the second monochromator again in the center of the beam. Now you can calculate the relation between movements of m2_xtal and monu. Move m2_xtal to the last known position (see table 7.3) and calculate where you have to move monu and move monu to this position. The first monochromator crystal is now aligned, a fine tuning will be done lateron. On the fluorescence screen the direct beam from the first crystal might be seen on the edge of the sreen. This is normal and depends on the position of montrav. If montrav is close to zero (it is not recommended to do the alignement at this position) the direct beam should be fully visible at one side of the fluorescence screen.


7.4 Alignement of the second monochromator crystal


Table 7.3: Positions of the crystals of the second monochromator (m2_xtal). A maximum of 5 monochromator crystals can be implemented. 3 crystals, matching the crystals of the first monochromator are implemented, one position is empty and one test crystal ((111)) is mounted. The positions in the next line are from the survey done by Peter Hiller in October 2000. The positions in the last line are from the alignement with the x-ray beam from march 2001.
Position 1 2 3 4 5
Crystal empty test crystal (311) (111) (331)
October 2000 194.68 164.68 134.68 104.68 74.68
March 2001     128.95 98.8 70.5


To find the reflected beam from the second monochromator crystal is straight forward because the fluorescence screen is very close to the crytsal and therefore it should only be necessary to scan motor mond. Once the beam is found the fluorescence screen can be taken out and the beam should be observable in the 6ID-D hutch. It might be necessary to optimize the undulator gap to get sufficient intensity from the diode.

If major work has been performed, for example the second monochromator crystals have been replaced it might be necessary to either scan m2_chi to adjust the height of the beam or to move m2_xtal to adjust the horizontal position of the beam. In the second case remember to adjust motor monu by the calculated dependence between monu and m2_xtal as described in section 7.3.

Once you have beam inside the hutch scan motor monu to make sure the maximum intensity is getting through. Now there is monochromatic beam inside the 6ID-D Side Station.

Now the fine tuning of the crystal positions has to be done. Make sure all slit systems in front of the first diode in the 6ID-D hutch are completely opend and all collimators are removed. Start macro mono_align_crysals. This command starts a macro which measures the beam position on the second crystal by changing $ \vartheta$ of the second crystal and doing a rocking scan with the first crystal. That way the bragg angle for the first crystal is determined under which the bragg condition for both crystals is fullfilled and the beam hits the second crystal in the center. The data of the performed scans has to be analysed externally, for example with the programm Spectra.

The beamposition in the hutch can be aligned in a similar way. Position a slit system that defines the beamposition in front of the pin diode. Now run scans where the position of the second monochromator crytal (motor m2_xtal) is moved by a few millimeter, adjust the $ \vartheta$ value of the first monochromator crystal accordingly and do a rocking curve with the second monochromator crystal. This will move the beam horizontally inside the hutch therefore it can be moved to the position it is supposed to be. After this alignement macro mono_align_crysals has to be repeated to make sure the beam is still centered on the second monochromator crystal.

This complete procedure has to be repeated for the other two monochromator crystal pairs.


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Next: 8. Equipment Protection System Up: html Previous: 6. Using the image   Contents   Index
Dirk Hupfeld 2001-12-20