UB Matrix for Triple Axis Instruments

> CELL a b c alpha beta gamma

set unit cell constants. If b or c are omitted, the same value as for a is used, if angles are omitted, they are set to 90 degress. Without arguments, the cell constants are listed.

> REF qh qk ql a4 a3 sgl sgu Ei Ef

Make an entry in the list of peaks. For angles and k-values not given, the current motor positions are used. If the given qhkl triple already exists, its list entry is overwritten. If not, a new entry is made. The peak number and the peak data are returned.

> REF CLEAR peak

Remove a peak.

> REF CLEAR ALL

Remove all peaks.

> REF

List all peaks.

> MAKEUB peak1 peak2

Calculate, activate and print out the UB matrix, as well as the peak list with qhkl values calculated back. peak1 is used as the main peak, i.e. driving to the angles given for this peak will correspond to a QHKL which may only differ by a scalar factor of about one, if the cell constants are not correct. peak2 is used only for determining the scattering plane.

It has to be checked that this is fully compatible with the TASMAD specification. In principle, AX,AY,AZ should correspond to peak1 and BX,BY,BZ to peak2.

>MAKEUBFROMCELL

Calculate and activate a UB which has been calculated from the cell constants alone. This is useful to get a4 when no reflection has yet been found to calculate a proper UB.

Markus Zolliker: there should be a an easy way helping the user to correct the cell constants (for example due to thermal contraction) according to the measured peak.

> LISTUB

List the UB matrix, the cell constants and all stored reflections.

Out Of Plane Operation

This formalism allows to drive out of the scattering plane using the tilt motors of the sample stage. Some cryostats cannot stand this. Therefore driving out of plane can be switched off and on.

> TASUB OUTOFPLANE 1

This command switches out of plane operation on.

> TASUB OUTOFPLANE 0

This command switches out of plane operation off.

> TASUB OUTOFPLANE

lists the current value of the outofplane variable

Example session:
(Some numbers might not be correct, as this module does not yet work in this form).

We enter cell values

   > CELL 2.88 2.88 2.88 90 90 90

Find the peak 2 0 0 and optimize it

   ...

Once we are at the maximum:

   > REF 2 0 0
   Peak   QH     QK     QL      A4      A3     SGL     SGU
   1    2.00   0.00   0.00   65.31  -87.21    1.25   -5.22

Find the peak 0 4 4 and optimize it.

   ...

Once we are at its maximum:

   > REF 0 4 4
   Peak   QH     QK     QL      A4      A3     SGL     SGU
   1    0.00   4.00   4.00   65.31  -87.21    1.25   -5.22
   
Show again the peak list:

   > REF
   Peak   QH     QK     QL      A4      A3     SGL     SGU
   1    2.00   0.00   0.00   65.31  -87.21    1.25   -5.22
   2    0.00   4.00   4.00   99.45   20.39    4.25   -1.22

Calculate the UB matrix, with 2 0 0 as primary peak and 0 4 4 as
secondary peak.

   > MAKEUB 1 2
   UB   2.456   0.530  -0.200
       -0.530   2.456  -0.090
        0.200   0.090   2.456
   Peak    QH     QK     QL      A4      A3     SGL     SGU     QH     QK     QL
   1 A   2.00   0.00   0.00   65.31  -87.21    1.25   -5.22   2.03   0.00   0.00
   2 B   0.00   4.00   4.00   99.45   20.39    4.25   -1.22   0.02   3.95   4.03

the last 3 columns above show the Q values calculated back from the angles.
We drive now to the 2 0 0 peak

   > DR QH 2 0 0
   > PR A4 A3 SGL SGU
   A4 =  64.218
   A3 = -87.515
   SGL =  2.258
   SGU = -3.217

The value of A4 has changed, because the cell constants do not match the values
given for the first peak. The value of A3 has changed by the same reason, and
in addition, because the the plane given by 2 0 0 and 0 4 4 is now tilted back
into in the scattering plane. For the latter reason SGU and SGL have changed also.

   > DR QH 3 3 3
   > PR A4 A3 SGL SGU
   A4 =  82.516
   A3 = -31.215
   SGL =  2.258
   SGU = -3.217

note that the values for SGU and SGU have not changed. The will not change
as long as we stay in the scattering plane (no drives to Q3) and as long
as the UB matrix has not changhed.

   > REF 3 3 3
   Peak   QH     QK     QL      A4      A3     SGL     SGU
   3    3.00   3.00   3.00   82.32  -31.25    2.26   -3.22
   > MAKEUB C B
   UB   2.456   0.530  -0.200
       -0.530   2.456  -0.090
        0.200   0.090   2.456
   Peak    QH     QK     QL      A4      A3     SGL     SGU     QH     QK     QL
   1     2.00   0.00   0.00   65.31  -87.21    1.25   -5.22   2.03   0.00   0.00
   2 B   0.00   4.00   4.00   99.45   20.39    4.25   -1.22   0.02   3.95   4.03
   3 A   3.00   3.00   3.00   82.32  -31.25    2.26   -3.22   3.00   3.00   3.00

We have calculated a new UB matrix, based on the peak 3 3 3 as primary and the
0 4 4 as secondary peak. The UB matrix has not changed, as we were already exactly
at 3 3 3.