Undulator versus Wiggler

A decision between an undulator and a wiggler for SAXS experiments has to be based on the optimum flux at the sample for a given SAXS resolution and the necessity to tune the wavelength for anomalous dispersion studies. The beamprofile should furthermore be rather symmetric at the aperture slits in order to get a comparable SAXS-resolution both in the horizontal and vertical directions. 

The photon emission of an undulator is concentrated into a central cone with halfwidth x (a), z (cr). (observation direction 0 = cp = 0) 

Corresponding values, together with the size of the beam at 30 m distance from the source point — calculated via Eq. 6 — are indicated in Table 2. ESRF 

The p-values are fixed by the magnet lattice [13]. It can be seen that — for constant ex, ez — the high-/ undulator is optimized for a small divergence, while the low-fi is optimized for a small source point. 

Evidently these type of sources result in a quite symmetric beamprofile at the aperture slits. The high P-undulator is, however, preferable if one wants to have the smallest possible aperture slits. 

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