After installation and before data collection can begin
for the first time, the apparatus must be aligned (Appendix
2) and calibrated (Section 5.). Calibration should
be done for each run. When this process is completed, the incident x-rays
are confined to a 100 x 100 micron beam centered on the sample.
Finally, the relation between channel number on the MCA and the
energy of the diffracted beam, as well as the d-spacing of the diffracting
lattice plane in the sample is established. This must be done independantly
for each of the 4 detectors, when they are part of the experiment.
After a sample is installed, the upper ram is lowered to a fixed position, the spacer block moved into position, and the upper ram raised against the spacer block. This is all done with relative low hydraulic pressure. The lower ram is then raised until the sample is contacted. These hydraulic operations are done with electrical remote controls. A diffraction spectrum is then taken at nominally zero pressure and room temperature.
Although the sequence of steps may vary, depending on the needs of the investigator, the most common sequence is to raise the pressure slowly until the desired pressure is reached, then raise the temperature. At many points during this procedure, the process is halted and a data set taken; data is normally collected for 300 seconds. As the lower ram is raised; the cell assembly is compressed, raising its center; hence, the Z-position of the pedestal must be moved to "follow" the sample. In addition, the sample may be temporarily "lost", so the pedestal must be moved in Y and Z to try to place the center of the sample in diffracting condition. A routine exists to oscillate the pedestal up and down (or in other directions, if desired) during data collection, to spread the diffraction over a larger area while maintaining precise diffraction conditions. This is useful if the sample is particularly granular. Refer to IDL Command Line Scripts for more details
The pressure-temperature path depends on the needs of the particular experimenter. After the final pressure and temperature are reached, the sample is usually "quenched" (rapidly cooled by switching off the power), and the pressure lowered. As the cell deforms plastically upon pressurization, the depressurization stage is frequently the most difficult; it must proceed slowly (1-4 hours), and "blowouts" are possible. The exact cause of these blowouts is not certain, but it may be due to the inability of the gaskets between the anvils to hold the cell in as the anvils are withdrawn.
In 2000, the VMS computer was retired and the programs ported to a PC. In 2002, an EPICS control system was adapted to the X17 environment, and the control software completely rewritten. The CAMAC is no longer used to house the XIA digital signal processor, it is still used to run the E500 motor controllers. EPICS itself runs on one or more IOCs (Input/Output Controller); one is a Motorola-driven card in the VME crate using an operating system is called vxWorks. Two others run on dedicated PCs, and are called "SoftIOCs", because the controller function is in software. When the VME crate is booted, the various initialization files are downloaded from another computer, currently a MacIntosh G5 running system 10.3 - a variant of Unix. The XIA digital signal processors are now run from a National Instruments PXI chassis. The PXI chassis communicates with one of the SoftIOCs via a fiber optics cable. There is also a Princetion digital camera which communicates with the other SoftIOC, also with a fiber optics cable.
Fill the detector with liquid nitrogen. It takes about 15 liters and about 24 hours to cool down completely. For best results, don't let the detector ever warm up. Insert the hose from the 25 liter nitrogen Dewar into the opening at the top of the detector cryostat. The 25 liter Dewar needs to have about 3 PSI internal pressure, which it will develop in about 12 hours if all valves on it are closed. If you are in a hurry, you can pressurize it with the tube from the nitrogen gas bottle inside the hutch.
In the hutch, there are two racks which should be on. Each of the following items should be left on, but you should check to make sure: In the left-hand rack (rack 1, from bottom to top):
In the right-hand rack (rack 2), from bottom to top:
Inside the hutch, but outside the racks, turn on the Princeton Coolsnap camera power supplies, the D-DIA Gauges power supply, and the Canberra NIM bin on top of the hydraulic system.
The X-17 CAMAC crate and the Linux PC (in the X17B1 area) are normally left on all the time; check that they are on. Also, check that the aperture switches are OFF.
All motors have individual power/enabling switches. All those you do not plan to use should be off.
Each stepper motor is driven by a motor controller module. Most of them are located in the several driver chassis. Some of these chassis are located in the right-hand electronics rack, and others (those for the side station) are located in a short rack near the double door.
Motors 1 and 2 require 2000 steps per revolution, while the rest require 1000 steps (see table A1 in the Appendix). The number of revolutions per user unit (mm or degrees) depends on the mechanical stages and varies from motor to motor. The number of steps per user unit is defined in the motors template file and can be displayed using all in the individual MEDM motor window.
Because it is very important that a motor not be driven accidentally, there are several levels of safety. Each motor or motor bank has switches to enable and control its power. If the motor is not enabled and/or not powered up, the computer may try to drive it, but the motor will not move. In this case, knowledge of the motor position will be lost, and the motor will not move. For motors 11 and 12, there are brakes which must be off for the motor to be driven.
This program creates and/or copies the necessary files to the directory in which you will save your data. Complete directions are in the Documentation directory of drive D: on the server. As of September, 2002, this is mapped as drive P: on the SAM computer (and all other computers at the beam line). This is still true as of March, 2008. You can access it here.
Click on the Startup icon, which will load the IDL Runtime version of Startup. Follow the on-screen directions. There are five buttons at the bottom of the window. Pressing the first one displays the information which has been entered. If there is missing data, you will be notified. Pressing the second one will display and print the information on a letter-sized sheet on the laser printer. The third one will print the label. Check these, and if they are correct, then press the fourth button, which will update the PVs which were set by the Startup program. The fifth button adds a record to the Rundata.log file and exits. If you made a minor mistake, you can edit the label file (RUNLABEL.PRN) and then print it by entering COPY RUNLABEL.PRN LPT1: at the command prompt of the server computer (be sure to include the colon!). Go to the Experiment Information window of the main MEDM control panel, and check that all the lines are correct. Operator Name should have the IDs of all the experimenters; Experiment Title should be a label which doesn't change for the entire run (i.e. for all the files in the current subdirectory). Experiment Comments 4 and 5 should be the chemistry and phase information entered in Startup. Experiment Comments 1, 2, and 3 are there for information which changes for each datafile; Experiment Comment 1 should be a brief label of a specific file (e.g. "Calibration using NaCl", etc).
Problems with getting the detection system to work is frequently due to unexpected changes in the switch settings.
Motor Driver Module for motors 17-24 (this is an incomplete copy of John's box)
Main Power :ON
Motor Driver Module for motors 1-8 (John's box)
Main Power :ON
Bank Power: both ON
Brakes: ON (switches down, lights off)
Individual power switches:
CAMAC Crate: ON
4 push-button switches (from left to right):
I/O Patch Panel no switches
Display Module no switches
2.4.3 DATA COLLECTION: CAMAC CRATE
We now have a 4-channel DSP which will have the equivalent of 4 DSA2000s. It is in the PXI chassis, and has no controls. This must be on. In the near future, we will have three of these, giving a total of 12 Digital Signal Processors. We will use ten of these for the new 10-element detector.
HIGH VOLTAGE POWER SUPPLY inside Canberra NIM bin
-300 volts for the 13 element detector, +500 volts for the single element detectors