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Reflectometer D17

D17 is the first ILL dedicated reflectometer and it has been designed to be as flexible as possible in resolution and modes of operation. The instrument is suitable for the analysis of surface structures in solids and solid/liquid interfaces. Horizontal surface experiments, such as free liquids, will suffer from a severe restriction in Q-range and flux and are thus not recommended for this instrument.

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D17 LAMP Book

AW_STARTMONO

AW_STARTMONO is a GUI for designing and configuring scans in monochromatic mode.

It will take your input and then create a job file that you can run directly from the MAD interface.


Help on the different fields is given below:

Directory Path contains the directory where the job and configuration files will be saved. 

It's wise to have your name directory here (e.g. /users/data/YOURNAME).  That way, you're guaranteed not to lose it, or have it accidentally overwritten in the future.

NOTE:  In order to run the job file, you must eventually copy it to /users/data/

Parameter file name contains previously saved configuration of the aw_startmono_old GUI.

Previous configurations of aw_startmono_old that have been saved can be reloaded.  Enter the appropriate file name in the field here and click on Get Parameters.

Lambda contains the wavelength in Ångströms.

The motor positions and count times are fixed in Q, so make sure this value is correct.

d(Lambda)/Lambda is the wavelength resolution.  This is only important if you wish to use a step size fixed by resolution.

Minimum Qz and Maximum Qz define the range of Qz for the specular reflectivity.  The positions for SAN will be calculated based on these values and Lambda.

DAN offset is used to calculate the detector positions.  See Scan type (below) for how this number is implemented.

Step size: There are two choices here:

Constant dQ, where dQ is the step size in Qz (defined for the specular reflectivity), which is typically much smaller than 1.

Fix by resolution, where aw_startmono estimates the resolution as a function of Qz (DAN = 2 × SAN + DAN offset, based on d(Lambda)/Lambda) and calculates the step size based on the value in No. pts in resolution, which should be an integer typically around 5.

Scan type:  There are three options here:

DAN fixed: will move DAN to DAN offset, and will simply scan SAN

theta-theta: will scan SAN and will move DAN = SAN + DAN offset

theta-twotheta: will scan SAN and will move DAN = 2 × SAN + DAN offset

Slit sizes:  There are three options here:

Fix constant, where the size sizes will remain fixed over the entire scan range.

Fix footprint, where the footprint on the sample will be constant at each point in the scan.

Fix S2W, where S2W is fixed and S3W will change to keep, as close as possible, a constant footprint on the sample.  This option more or less uses S3W as a background slit, with the angular resolution being determined by S2W and the projected width of the sample.

More information on these choices here.

Counting on:  You may choose time or monitor.

at intervals:  You have two options here:


Constant, where you enter a number in the preset.  Each point in the scan will be counted for this long, either in time or monitor (whatever you chose in the field just above).

{t/m}=a(b+c*Qz^d), which calculates a count preset at each point in the scan based on Qz.  Seeing as how reflectivity falls as ~Qz–4, this option allows you to maintain reasonable statistics at large Qz.  Enter the appropriate constants in a, b, c, and d.  The count presets at the minimum and maximum Qz will be shown in the fields on the far right.

Polarization option:  There are four options here:

None:  A simple scan with no manipulation of the flippers

F1 on/off (no analyser):  Two measurements with the first flipper on and off at each point in Qz.

Supermirror analyser:  Four measurements with each of the combinations of the flippers before and after the sample.

3He analyser:  Seven measurements (yes, 7!) with the four flipper combinations, structured in such a way as the time dependence of the 3He cell will be compensated at each point in Qz.

More on the various options here.

The next three fields are diagnostics:

Total number of Q points shows you just that.

Total measurement time adds up all the count times and gives you an idea of how long the scan will take.  It does NOT account for movement time, so the total time for the scan WILL be longer than the number given here!

Monitor counts/second.  Obviously, if you've chosen to count on  'monitor', you need to put in an estimate in here to get an idea of the total count time.

Write job file.  Once you're happy with your job set up, you need to write the job file to be run from the MAD interface.  Enter the name you want here and click on the button to save it.

Save configuration:  Once you're happy with your job set up, you can also save all the parameters in the fields of the GUI.  They can be reloaded in future, when you want to tweak your job parameters another time.

Close STARTMONO, pretty self-explanatory, no?