Once every semester it is useful to check out whether the monochromator energy resolution is optimised. The exepriment is easy. Using the W{110} crystal one measures in dispersive plane the W 4f core level emission for various photon energy (say 80, 110, 160, 200, 240 eV) using grating 1 (VLS 200). A different core level can be used using grating 2 (e.g. Rh 3d). In principle, keeping the photon energy constant, the mirror and the grating angles have to be varied in order to minimise the beamline contribution to the Gaussian broadening of the W 4f peak. Suitable angle variation are obtained by moving the grating and/or mirror by about 0.1 mm. To find an example of this procedure, have a look at Labbook No. 15, 13-21 July 2004.

The optimisation of the monochromator front mirror MUST be the same when using grating 1 (VLS 200) and grating 2 (VLS 400). So, if grating 1 works fine and grating 2 seems to have lost its calibration, just move the grating 2 stepper until when the core level under study has got approximately the kinetic energy you expect. Then move in smaller steps (0.1 mm) and choose the angular value which gives the best energetic resolution. In order to do this, use BCSJAVA/monochromator and select the "show details" checkbox in the set energy section. After clicking, the mirror and grating angle will appear. Calculate the angular variation between the BCS nominal value and the best energetic resolution value. This number represents the correction one has to input in the MONOCH3 protocol in the BCS program.

This correction has to be input by editing the code controlling the monochromator on the BCS. This can be modified using the monochromator wizard, available at the link below:

http://adam.elettra.trieste.it/projects/mono/monoch/monoch_cfg.cgi

The wizard is protected by a password. (Do you know it?).

In input of the program, modify the float variables deltaMaMi and deltaMaGr (for grating1 and grating2 CLASS) according to the anguar differences measured in the experiments:

/* -------------- M I R R O R --- O P T I C S ----------------------------*/
Mirror CLASS {
..................................................................
deltaMaMi FLOAT -27.745; /* 27 July 2006 - best for 500 eV */
};

/*-------------- G R A T I N G 1 -------------------------*/
Grating1 CLASS {
.................................................................
deltaMaGr FLOAT 22.7685; /* 27 July 2006 - best for 250 eV */
};

/*-------------- G R A T I N G 2 -------------------------*/
Grating2 CLASS {
.................................................................
deltaMaGr FLOAT 22.7910; /* 27 July 2006 best for 500 eV */
};

Once you save the file (please comment changes done and save old parameters), you need to wait for 60 seconds. This time is necessary for the nfs cache (of the BCS computer) to be emptied. Then press the button "reload", to order the BCS to reload the input parameters of the monocromator protocol.