Prerequisite to the operation of an electron storage ring as a primary source standard is - in addition
to sufficient stability of the storage ring - the knowledge of the parameters needed for the calculation.
The spectral photon flux *Φ*_{E} for a photon energy *E* is given by the Schwinger equation which
can be expressed schematically as:

The storage ring parameters are:

- electron beam current*I*,

- electron energy*W*,

- magnetic induction at the source point*B*,

- electron beam effective vertical size*Σ*_{y}.

The storage rings parameters have to be measured with high accuracy in order to calculate the spectral output with a low uncertainty. In practice the spectral photon flux through an aperture is calculated and therefore also the emission angle*Ψ* and the geometry parameters determining the angular
acceptance have to be measured, i.e. the distance from the source point *d* and the aperture size
(e. g. *a* • *b* for a rectangular aperture).

- electron beam current

- electron energy

- magnetic induction at the source point

- electron beam effective vertical size

The storage rings parameters have to be measured with high accuracy in order to calculate the spectral output with a low uncertainty. In practice the spectral photon flux through an aperture is calculated and therefore also the emission angle

last update: 2011-09-30