The liquid surface spectrometer, constructed at BNL Physics, is designed to allow x-ray scattering from liquid samples. The spectrometer has two stages, one with a steering crystal which uses a Bragg reflection to deflect the beam downwards onto a horizontal sample, and a moving sample stage to intercept the beam and support the detector arm. A BNL/Harvard collaboration manages a similar instrument at NSLS beamline X22B.

During this X25 run we tested the spectrometer and performed the first resonant x-ray scattering measurements from liquid metal surfaces, at the L_III edges of Au and Bi in liquid Hg-Au and Bi-In alloys. Read here about the experiments. A nice set of pictures was taken during the run, they'll be posted here as soon as possible.

In this memo:

• Motor notes
• Geometry code
• Alignment and gizmos
• Shopping List

In comparison to the other liquid spectrometers, this instrument is very sweet. Congratulations to those responsible for the excellent design, and thanks to everyone who helped work on it.

Motor notes

We installed four-phase motors in order to avoid having to reconfigure the drivers at X25. Everything moved well except for the sample z stage, steering crystal chi, and steering crystal phi-x translation, and we also would prefer more resolution on the steering crystal stage positioning motors. We expect that going to the three-phase motors will provide the additional torque and resolution required, so at the moment, we aren't specifying any changes in gear reducers.

Installation of the three-phase motors requires:

1. Choosing, purchasing and attaching motor cable connectors
2. Setting up the driver/controller hardware
3. Testing all motions again
4. Testing the spec/epics/motor interface

The first two items can be done at BNL, the third can be done here with a limited choice of motor parameters, and the last needs to be done at Argonne. We also thought of a few mechanical modifications that haven't been finished:

1. Longer blocks to space sample stage further from the steering crystal stage
2. Table height motor control box
3. Rudder for driving the thing
4. Bracket on dovetail cover plate for vibration isolation (the vibration isolation unit works very well!)

(Back to the top.)

Geometry code

The Surf code to govern the scattering geometry was finalized during this run. The beam tracking is very good with this machine! Unlike any other liquid surface spectrometer we have experience with, with this machine we were able to change the energy and just continue to measure without adjusting any of the centering positions or tracking parameters. For more information about this scattering configuraion, see the X22B LSS homepage.

We didn't trust the alignment enough to attempt to do energy scans at fixed position, but I did play with it a little, and found that the fixq option in Escan doesn't seem to work in Surf. I might look into this, although nobody will be clamoring for it.

To do:

1. Make a few cosmetic changes to the Surf macro files
2. Ship them to Gerry to be included in the standard distribution
3. Install Surf (the Spec configuration for liquid surface scattering)
4. Test Surf with the spectrometer at CMC.

(Back to the top.)

Alignment and gizmos

Although tracking was good, it wasn't perfect. Since the deviations of the beam position were very small, the source is unclear, but it is probably a combination of things like concentricity of the circles and orientation/position relative to the beam.

Steps we shouldn't skip, and helpful gizmos, are

1. Something to test whether the circles are concentric
2. Modify (i.e. make uasble) the piece to hold a pin in the sample stage, and set the incident horizontal slits around this position.
3. Make a pin to mount in the ir and or stages to set the height
4. Obtain an azimuthally mounted bit of Ge(111) for setting the theta zero
5. Modify the crosshair and foil mounts in the crystal stage to be both more adjustable and more stable.

(Back to the top.)

Shopping list

We had to borrow the following from X22B or X25. Either CMC or the liquid spectrometer itself should own these things:

1. Detectors (bicrons, ion chambers)
2. Ion chamber mount for X95 flight path, to fit beside slits
3. Motorized slits
4. Motorized filter wheel and set of filters for different energies
5. Auto-level telescope on a stable, heavy stand
6. TV camera and bracket for mounting on the X95 flight paths
7. Metal foils for scanning the energy to find the absorption edges
8. Air hoses and fittings for evacuation of flight paths and for running compressed air to the airpads (which work great, by the way!)

(Back to the top.)