This run featured several firsts. We used both the primary and secondary vertical mirrors, tested the new Soller slits that were custom made at RISO, and installed a translation stage to mitigate the effects of radiation damage on our sample.
Mirrors. We chose to work at 8.00 keV with an unfocused primary mirror and the secondary mirror positioned at 0.18 deg to suppress higher harmonics in the beam. This resulted in the beam entering the C-hutch at a height just barely within the range of motion of the xtalht motor. Instead of jacking up the entire LSS, we decreased the mirror tilt by 0.2 mrad and so lowered the beam by about 5 mm. We laterdiscovered that the sample height travel was too limited (by about 10 cm) to position the trough in the beam. We began by mounting the trough on top of lab jacks on the vibration isolation stage, and later replaced the lab jacks with a horizontal translation stage (see below). The secondary mirror was very effective. We observed the spectrum of the incident beam by connecting a bicron detector to a multi-channel analyzer and found that less than 2% of the beam was at the third harmonic.
Soller slits. For the experiment, we wanted to be able to switch back and forth between reflectivity and GID measurments, so we mounted two bicron detectors on the output arm of the LSS. The reflectivity detector was behind the usual output beam pipe while the inplane detector was mounted behind the new RISO Soller slits, which were clamped onto the output beam pipe. Some modifications to the Soller slits were necessary. We changed the motor connectors and vacuum line connection to ones in common use at CMC CAT. We had some spacer/adapter plates made so that we could mount the bicron (with a full set of XIA slits in front of it) to the rear of the Soller slits and to make sure that the slits cleared the output rotation stage. The kapton exit window popped when we first pumped down a vacuum. Rather than worry about getting a replacement window vacuum tight, we taped some kapton over the exit window and put a small slit in it near the bottom to allow us to circulate helium in the slits instead of evacuating them. The three motions of the slits (soller inboard (sib), soller outboard (sob) and soller x (sox)) were interfaced with EPICS and Spec. The XIA slits before the inplane detector became the slit 4 assembly in EPICS and Spec. The weight of the Soller slits eventually caused the coupling to the or motor to slip. Smooth operation was restored by balancing the load with a counterweight. In order to accommodate this arrangement, the output arm had to be moved about 100 mm away from the sample stage. We also set the parameters for the or motor to be slower. When the new linear detector is installed, it will be necessary to re-balance the load. Beefing up the coupling between the motor and the shaft might also be a good idea. Overall, the Sollers worked well. It was great that they are mounted in a way that ensures tha thet vanes are parallel to the beam.
GID.We found that radiation damage could destroy the GID from the alkyl chains of the phospholipid quite rapidly, so that a 15-minute scan could not be reproduced. We used a translation stage to move the sample transverse to the beam and expose new areas of the sample between measurements and we were careful to fill the trough with He before taking data. Unfortuantely, it took about an hour for the trough to fill with He completley and for the background scattering level to bottom out. In the future, it would be good to find a way to minimize this time while also conserving He. Our best GID (from the alkyl chains) had about 2500 cps in the peak on a background of about 100 cps.
Attenuator We removed the copper foils Ben had installed on the attenuator bar and replaced them with 1-10x 3 layers of aluminum foil, 0.00185" thick, and got a wheel factor of about 4.7.
Glass block. We used a glass block about 150x100 mm that was ground at Penn. This block (along with two blocks Ben had made at BNL) will stay at CMC CAT.