DORIS III is an electron-positron storage ring which was originally designed
primarily for high energy physics
experiments involving 
collisions but was also used as a
source of synchrotron radiation in
experiments covering a wide range of topics.
Up until May '93 DORIS III alternated between two modes of operation. In parasitic mode
the ring was typically run at energies of 
and stored both electrons and positrons.
Priority was given to high energy physics experiments but synchrotron radiation was
still available. In dedicated mode the ring was operated at lower energies of
around 
with only electrons used to supply synchrotron
radiation to beam lines at the wiggler and bending magnet
stations. After May 1993 the source became dedicated to the production of
synchrotron radiation. The consequences
were an improvement in source stability leading to higher electron currents
and a smaller source size. Table 
shows the typical
operating parameters of DORIS III for the three cases mentioned above. The parameters shown
are the electron energy at which the ring is operated; the critical energy, 
, of the ring
defined as that energy which bisects the distribution of radiated power of the synchrotron, (i.e.
half of the total radiated power is above and half below); the current circulating as
electrons in the ring, 
; the radiated power in one milliradian of horizontal arc at maximum ;
the number of electron bunches circulating in the ring at any one time; the typical electron beam
lifetime; and the emittance defined as the area of the phase space ellipse describing the positional
and orientation distribution of the particle trajectories.
Table: DORIS III storage ring parameters in both modes of operation.
Figure: Bending and Wiggler magnet lines of the DORIS III storage
at DESY in Hamburg (kindly provided by Dr H. Brefeld, HASYLAB.
Fig. shows the position of the wigglers and bending
magnets around the storage ring. The two bending magnets, 
and 
, support
six of the EMBL beam lines, two of which, X31 and X11, are used solely
for protein crystallography.