The detector system on Station 9.6 has its own locally built table. It has to be driven in the vertical and horizontal directions in order to maximise the alignment between the synchrotron beam and the internal collimation system of the detector being used. There are several motors used to do this, all of which are controlled through the beam alignment software pxgen++.
There are two ion chambers, supplied by MAR, that produce a reading on the black display terminal in the User area outside the hutch. CHAMBER1 (IC1) is situated immediately after the first set of slits on the camera, and is on the input side, closer to the source. Similarly, CHAMBER2 (IC2) is situated after the second set of slits, on the crystal side. If the display shows no reading, check that the port and station shutter are both open.
The program may be started by typing pxgen++ at the prompt. Select the "Optimize Beam" tab.
A schematic of the table is shown. It is possible to move the following motors:
A motor is selected by clicking on the appropriate arrow on the table schematic. To move the motor, first select the mode By with an increment of 50, units of Microns and Slow speed. The motor can then be moved by clicking on the + or the - button or by clicking on the Start Move button. It may be a good idea to record the motor positions at the beginning. Thus it will be possible to get back to the 'starting point' should some disaster occur!
It is recommended that you start by optimising the reading of IC1 by moving just the front vertical and front horizontal motors. When this value has been optimised, switch to IC2 and optimise this using the Yaw and Pitch options. These movements will maintain the reading of IC1 and allow IC2 to be optimised. An increment value of 10 to 20 mDeg should be used for Yaw and Pitch.
Moving the horizontal pre-mono slits will change the horizontal crossfire of the beam hitting the monochromator, also changing the intensities on the ion chambers proportionally. Reduction of the crossfire will allow better resolution of spots in the horizontal direction. This is probably only needed for crystals with very large cell dimensions. When reducing the cross-fire, the slits should clip the beam evenly on both sides, i.e., one slit should reduce intensity by 25%, for example, and the other slit by another 25% of the original reading. Please remember to make a note of any changes to these slits in the log book.
If the terminal shows no reading, check that the station shutter is open. If there still is no reading, you should open up the camera slits to around 1 mm. The drums controlling the slit width adjustment have two dials on either side of a central rail. The outer dial reads in full mm, and the inner dial reads in fractions of mm.
Proceed to maximise the ion chamber reading by driving the table motors. There should be some reading with the slits set that wide. If it is a faint reading, try using gain x100. Only major disasters may be invoked as a reason for failing to get a reading by now. You should proceed to maximise the reading on CHAMBER2. Reduce the slit widths gradually, and repeat until you have optimised the reading through the slits set at the desired width.
If the ion-chamber display goes blank, it is an indication that the continuity of the signal from the ion chambers has been interrupted. Check the cables, and make sure they are correctly plugged into their sockets. One possible area where they may become disconnected is inside the hutch to the right of the door. The normal interlocking procedure involves the User going round that corner to reach Search Point A. If in so doing the blue cable was nudged, it might be dislodged from its socket in the panel, and should be reinserted.