The spectrometer consists of a 7-meter arm rotating in the horizontal plane and equipped with five spherical crystal analysers. With this spectrometer we have the capability to record spectra at five momentum transfers simultaneously. The realisation of the 12-meter arm is an ongoing project and once coupled with the 7-meter arm it will provide the capability to record spectra at nine momentum transfers simultaneously.

Table below summarises the main characteristics of the ID28 Beamline with the 7-m arm:

Reflection Energy
[keV]		 deltaE
[meV]		 Qmax
[nm-1]		 Qmin
[nm-1]		 deltaQ
[nm-1]		 Flux
[ph./s/200 mA]
Si(7,7,7) 13.840 7.6 ± .2 64 1 1.89 10.5.1010
Si(8,8,8) 15.817 5.5 ± .2 74 1 2.16 9.00.1010
Si(9,9,9) 17.794 3.0 ± .2 83 1 2.43 2.70.1010
Si(11,11,11) 21.747 1.5 ± .1 101 1 3.00 6.60.109
Si(12,12,12) 23.725 1.3 ± .1 111 1 3.24 5.85.109
Si(13,13,13) 25.704 1.0 ± .1 120 1 3.50 1.47.109

Energy indicate the photon incident energy; DeltaE is the total energy resolution; Qmax and Qmin indicate the maximum and minimum measurable momentum transfer; DeltaQ indicates the Q-spacing between adjacent analysers; the Photon Flux values are measured at the sample goniometer with the following experimental conditions: two 1.6 m U32 undulators; ring current: 200 mA; primary slits aperture: 1.6 mm (horizontal) x 0.7 mm (vertical); secondary slits aperture: 2.4 mm (horizontal) x 1.0 mm (vertical).

The Qmin depends strongly from the beam divergence (40 Murad hor. x 20 Murad ver.) and from the aperture of the slits in front of the first analyser.

The focal spot size at the sample is 250 Mum hor. x 80 Mum ver. using the toroidal part of the focussing mirror and 25 Mum hor. x 60 Mum ver. using the cylindrical part of the mirror for the vertical focussing and the multilayer mirror for the horizontal focussing