Thanks as usual to the onsite staff and the previous users, who did nice jobs of documenting the last year's runs.
We really ought to put all the operations notes in chronological order on the CMC website sometime. Meanwhile, be aware that the x-ray group server "solids" will soon be inaccessible from outside BNL. You should be viewing these pages from our new home base, www.solids.bnl.gov. Please change all bookmarks that point to solids.phy.bnl.gov !
I am writing this halfway through the run (10 september).
Spec 5.00.04 was installed. This version incorporates the new array data structure for scan data. All SURF and FOURC users should start fresh (invoke with -f option) to input the new macros. Be aware of user macros breaking if they referenced the old scan data groups explicitly -- and rewrite them!
This version of Spec has a command called plotselect that takes as an argument one of the counter mnemonics. It appears to be required in addition to resetting the DET variable: For example, DET=ion2 sets ion chamber 2 as the detector, but plotselect ion2 is also required to have Spec plot the counts in ion2 if it was using something else before. I need to ask Gerry whether this is a bug. (Sure seems like one.)
As I write this, the psd macros have not yet been implemented though it's planned for this run.
Several users in a row voted the XIA slit controllers off the beamline, and these have been replaced with ordinary motor controllers on the liquid spectrometer flight paths. To avoid duplicate names with motors in the B hutch, we have renamed the incident and detector slits slit7 and slit8 respectively, and made changes to slit.mac to display all configured slits (B and C hutches). In future we may want to redefine the display macros, but we should be aware that occasional users do odd things (like using the LSS with Fourc) and might need unexpected combinations of slits for this reason.
Our experiment involves arachidic acid langmuir films and mineral crystals nucleating at the interface. We were concerned about both beam damage and harmonic rejection (my favorite obsession). To ameliorate both, without changing the mirror position, we decided to do the experiment at 10 keV. We also defocussed in the horizontal, changing mirhbend from 50,000 to 10,000. At the high values, the beam shape (seen at the LSS detector in the C hutch) is roughly triangular. At 10,000 the peak intensity decreases by a factor of two and is flat across the top, without too much structure. Intermediate values looked worse, flat with a pointy bump sitting in the middle. Yes, a picture would be worth a thousand words here. Let's see how the data look and then decide whether this is a useful configuration.
We had a problem with the spectrometer position again: this time, since the beam comes slightly lower into the hutch than before, the incident flight path post is high enough to hit the theta stage at an even smaller value of two-theta. In fact, I can only get about 0.4 degrees past the zero position at 10 keV, so it's a good thing we aren't at 8 keV instead. As it is, the lineup scans I want to do are impeded. My horizontal input slits are 5mm wide because I defocussed the beam. Backlash prevents going anywhere in the positive two-theta direction.
We're borrowing the 10 keV attenuator bar from X22B and need to make one for CMC.
Please buy me a real oscilloscope, with a cathode ray tube in it.
I hooked up a pump to the soller slit assembly, patching the small slit in the kapton so I could pump it out. Overnight, the kapton broke and tore into the collimator films! About half of the foils were completely destroyed. We took the unit apart, removed the broken films, and sorted the survivors into "unharmed" and "torn at the edges". The intact films were put back in with the coarse resolution setting (separated by two aluminum spacers). I cut about 1.25 inches from one end of any film with an edge torn by less than that, and put these back together with the fine (one spacer) setting. The remaining aluminum spacers fill up the middle.
Well, Ben always said he wanted to have made the set with three settings (coarse, fine, and open gap); and Thomas and I always said we wondered what the guts of the soller slits look like; now we got our wishes. When I put the assembly back together and put the tension on the blades, they straightened out pretty nicely. Looking down the collimators, they aren't perfect, but they don't seem much worse than our "good" ones at X22B. The fine, coarse and open regions all have about the same widths (5mm). We'll test them this week and see what they look like. If we have to have them replaced or repaired -- well, there goes my oscilloscope with the cathode ray tube in it.
Didn't finish testing it yet (10 September 2001). We did start up the gas and the electronics, put it in the beam and get the counts, but I can't tell you what it looks like on the sample.
I promised in the last memo (June 2000) that there'd be a web page for the experiment on clays eventually!