D2AM Material science Diffractometer

• Overview of the experiment.
• Description of the 7 circles goniometer.
• Sample environments.
• Detectors available.
• Filters to attenuate the direct beam.
• Description the goniometer slits system.

Overview of the experiment.

The material science diffractometer is a general purpose instrument which was designed to record intensities over a wide dynamical range. It consists of 7 circles allowing users to record data in and out of the polarization plane. The whole instrument lies on a table used for its alignment.

The (x,y,z) axis are defined on Figure 1.

Fig 1	Fig 2

• The sample can be oriented through 3 circles of the instrument :
1. THETA : sample rotation around a horizontal axis perpendicular to the incident beam (y).
2. CHI : sample rotation around x, it is carried by THETA. On figure 1 chi=90.
3. PHI : sample rotation around the sample normal. It is carried by CHI and THETA, so that the sample lies horizontal at chi=90 (its normal is z) and vertical at chi=0 (its normal is then y). Note that at CHI=0, THETA and PHI axis are parallel and horizontal.
• The detection line uses the 4 remaining circles. 2 of them adjust the position of the detector arm in and out of the diffraction plane. The 2 last are used to set the analyser at the right energy.
1. ALPHA : horizontal motion of the detector arm to allow measurement out of the polarization plane, its full use needs a special configuration of the experiment control program.
2. 2THETA ( or tth ) : vertical motion of the detector arm. It is carried by ALPHA.
3. THETA_A ( or omegaa ) : bragg angle for the analyser cristal, carried by detector arm.
4. 2THETA_A ( or ttha ) : vertical motion of the detector after the analysing crystal.

Description of the 7 circles goniometer.

The main characteristics of the 7 axis are listed below, units and angular values are user values expressed in physical values:

The spec macro get_7csettings can be used to ensure that user and dial values agree, It use the data file 7c_settings.db of your directory or the standard one (~/specadm/d2_macros/7c_settings.db).

You can get a complementary description of motor axis.

Sample environments available :

• A simple z-motorized sample holder , on which a huber goniometer head can be mounted. Its allows to keep a good confusion sphere.
• An x,y,z-motorized sample holder using the same goniometer head as previous holder.
On both last holders, at room temperature, a vacuum chamber with a 80mm diameter Be hemisphere can be used to reduce the sources of diffusion, still allowing a wide access to the reciprocal space.
• A Displex cryostat (15-300K) with Be hemispheres. When it is used, the angular range available for PHI and CHI are restricted to avoid collision. PHI can only be moved from -60 to +60 and CHI from -5 to 95.
• About the cryostat used on the goniometer
• About the high temperature reaction chamber (Anton Parr XRK 900) for powder studies
• here is a pdf document describing size available around the goniometer center.