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Procedure for X-ray Beam Alignment Beam
alignment is especially necessary after filament
change. Assuming the machine has been powered
up, you start preparing for beam alignment by doint the following.Move the readout system back to give you a confortable room to work. Put the x-ray pinometer, as shown in the figure, on the track of the readout system and turn the switch of the pinometer's base to the left. This will turn on the magnet in the base to secure the position of the pinometer on the track. Now, put the pinometer's detecting "tip" very next to the pinhole of the collimator. This allows you to get the x-ray beam and send it the to PDA-18 meter, which you should make sure is connected to the pinometer. Next, turn the AXIS SELECTOR of the mirror optics controls box to position 4 (FILTER WHEEL). Turn on the power of the box and use the FORWARD/REVERSE (F/R) switch to turn the filter wheel in the mirror box (you need to watch how it turns) to the OPEN position. Then, turn on the POWER of the PDA-18 METER. Locate the shutter switch of the x-ray (two of them on the front panel of the machine next to the X-RAY control panel). Turn the switch on the right all the way up to open the shutter. Now, you should see some reading on the PDA-18 meter. This is your starting point. At this point, the actual x-ray beam may look like this with respect to the position of the collimator's pinhole (the black dot at the center of the picture). Now follow the instructions step by step to align the beam.
You'll have to work with the MIRROR OPTICS CONTROL box and the PDA-18
METER shown here. Make sure these "toys" are connected to power.  Step
1. Open up slits (AXIS SELECTOR at positions 3 and 5)Turn F/R switch to REVERSE position and SPEED knob at a reasonable setting. Watch PDA-18 reading increasing until it reaches a maximal. You expect an actual beam like what the picture on the right shows. If you do not see the two perpendicular bright lines, the BIAS setting (next to the VACUUM panel) is probably at 0. Turn it to 3.5.  Step
2. Translate Mirror 1 (AXIS SELECTOR at position 1)Turn F/R switch back-and-forth until you see the PDA-18 reading reaches a new maximal. The actual beam now looks like the picture on the right, and you've moved the horizontal bright line onto the pinhole.  Step
3. Translate Mirror 2 (AXIS SELECTOR at position 7)Do the same as Step 2 to get new maximal PDA-18 reading. Beam position looks even better now - the pinhole is at the cross of the two bright lines. That's where you get the highest beam intensity. However, the beam probably is not in focus yet.  Step
4. Focus Mirror 1 (AXIS SELECTOR position 2)Turn F/R switch back-and-forth again. You should see PDA-18 reading increase again, though not as dramatically as you do when you tranlate the mirrors. The beam becomes more concentrated now.  Step
5. Focus Mirror 2 (AXIS SELECTOR position 6)The same game as above but to Mirror 2 this time. Now, both bright lines are well focused.  Step
6. Close down horizontal slit (AXIS SELECTOR position 3)Turn F/R switch to FORWARD position and watch PDA-18 reading dropping. First, it'll drop quickly. Then, at some point it'll stop dropping even though you do not release F/R switch. Finally, it starts dropping again. You want to leave the slit opening right at where the reading starts dropping the second time. You may have to do this a couple of times to make sure it's done correctly. Reduce the SPEED if necessary. This step (as well as the next) is absolutely essential because it gives you the highest possible intensity as well as best possible monochromaticity. Now, the beam looks like what shows on the right.  Step
7. Close down horizontal slit (AXIS SELECTOR postion 5)The same game for the other slit, and you finally get the beam right!!! After this step, you may need to go back to fine tune the translations and focuses to make sure you are get a peak beam intensity. After you are done, don't forget to turn the shutter switch back to EXT. position (all the way down) |
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