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 and the 2-theta circle. The exit slit assembly, which is fixed relative to the 2-theta circle, defines the diffracted beam to within 100 microns. 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.
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. 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), to spread the diffraction over a larger area while maintaining precise diffraction conditions. This is useful if the sample is particularly granular. In addition, another routine exists which collects many diffraction spectra in rapid succession, say one every 30 seconds or so, in order to study kinetics of phase transformations.
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.
The operation of SAM85 in conjunction with the synchrotron currently requires the use of programs running on a VAXstation 3100 running VMS. This computer is interfaced with two CAMAC crates, one which is part of the X17 beam line, and another, the SUNY crate, which controls SAM itself. The X-17 crate controls the upstream apertures and the monochromator. The SUNY crate runs the motor assemblies on SAM and the Canberra Series 35 multichannel analyzer.
Fill the detector with liquid nitrogen. It takes about 4 liters and about two hours to cool down completely. For best results, don't let the detector ever warm up. The easiest way to do this is to connect a hose from the 25 liter nitrogen dewar to the inlet pipe. Make sure the outlet pipe is pointing down, so condensed water won't flow into the detector dewar.
There are three front panel switches for each bank of motor drivers.
Bottom switch labeled MAN-OFF-ON is the power switch and should be ON.
Middle switch labeled MAN-REM should be on MAN.
Top switch labeled OFF-ENA should be OFF until you are ready to drive that bank of motors.
Each stepper motor is driven by a motor controller module. The modules for base (were purchased in Japan and run on 100 volts, hence the large transformers. The other modules (for motors 1-8 and 14-16) were acquired here and run on 117 volts.
Motors 1, 2 and 14 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 parameter file (see Table II), and can be displayed with the command DM (display motors).
Because it is very important that a motor not be driven accidently, there are several levels of safety. First, each motor has a "fixing parameter" established in the SAM85 program. If this is set to 1, the motor cannot be driven. Secondly, 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 the base motors, it is more important that the motors not move than that their position be known, so the enable switch for these motors should be OFF. Finally, for motors 7 and 8, there are brakes which must be off for the motor to be driven. Never disengage either brake if the corresponding motor power is off!
For motors 1-8, there is a main power switch, one switch for each of the two banks (1-4 and 5-8), and individual power switches. The main switch position is detected on program startup, and must be on. Individual switches are checked when the corresponding moter is driven. Bank switches are never checked.
Problems with getting the detection system to work is frequently due to unexpected changes in the switch settings.
The panels/modules are listed from top to bottom. See figures 2 and 3.
A/D Converter Patch Panel: no switches
Motor Driver Module (motors 4-12)
Top 3 motor enable switches: ENA
Middle 3 MAN-REM switches: MAN
Bottom 3 MAN switches: ON
Upper brake switch: OFF (brake on)
Lower brake switch: ON (brake on)
(both brake lights should be off)
Motor Driver Module (motors 1-3)
both modules ON
CAMAC Crate: ON
4 push-button switches (from left to right): IN, OUT, OUT, IN
I/O Patch Panel no switches
The panels/modules are listed from top to bottom. See figures 2 and 4.
Display Module no switches
DC-Frequency Converter 1 for voltage
Power ON
Full Scale Input 10 Volts
DC-Frequency Converter 2 for current
Power ON
Full Scale Input 1 Volt
Heater Power Control
Power ON
Enable: ON or ENABLE
Current Controls: CCW
Main Transformers
All 3 switches ON
The following list is not meant to be gospel, but a good starting point for troubleshooting. The settings will give a calibration of ~15 channels/keV (the 122 keV Co57 peak will be at channel 1830).
2020 Spectroscopy Amplifier
FINE GAIN: 886
COARSE GAIN: 30
POLARITY: -
RESTORER: HI, SYM
THRESHOLD: AUTO
PUR: OFF
SHAPING MULTIPLIER: X1
TIME: 4 Ms
HIGH VOLTAGE POWER SUPPLY
500 volts
MEMORY SEGMENT: 1/2
ADC GAIN: 2048
AMP GAIN: NOT NEEDED
LLD 0 (may be increased to ~0.20 to eliminate low energy counts)
ADC OFFSETS: ALL OFF
ADC INPUT (on rear): EXT