The operation with high current, a low emittance electron beam and the use of long undulators allows a number of ESRF beamlines to be run with both high spectral flux and high spectral brilliance.
 

The main parameters of the electron beam in the storage ring are summarised below :

Energy
GeV
6.04
Maximum Current
mA
200
Horizontal Emittance
nm
4
Vertical Emittance
pm
4
Coupling
%

0.1

Revolution frequency
kHz
355
Number of bunches
 

1 to 992
Time between bunches
ns
2816 to 2.82

The lifetime, bunch length and energy spread depend on the filling pattern. They are given below for a few representative filling patterns. In both the 16 bunch and the single bunch modes, the energy spread and bunch length decay with the current, the value indicated in the table corresponding to the maximum current. The bunch lengths are given for the usual RF accelerating voltage of 8 MV.

Filling pattern bunch
Uniform
16-bunch
Single
Maximum current (mA)
200
90
20
Lifetime (hours)
75
9
6
Rms energy spread (%)
0.11
0.12
0.22
Rms bunch length (ps)
20
48
73


The main optics functions, electron beam sizes and divergences, at the various points are given below. For insertion device source points, the beta functions, dispersion, sizes and divergences are computed in the middle of the straight section. Two representative source points of bending magnet radiation have been selected corresponding to an angle of observation of 3 mrad (9 mrad) from the exit, they correspond to different fields. Electron beam profiles are Gaussian and the size and divergence are presented in terms of rms quantities. The associated fwhm sizes and divergences are 2.35 times larger. Beam sizes and divergences are given for the uniform filling modes and apply to almost all filling patterns, except the single bunch for which a slightly larger size and divergence is reached due to the increased energy spread of the electron beam.



Even ID section
(ID2, ID6,...)
Odd ID section
(ID1, ID3,...)
Bending Magnet (3mrad)
Bending Magnet (9mrad)
Field
(T)
depends on ID
depends on ID
0.4
0.85
Horiz. Beta Functions
(m)
35.2
0.5
1.41
0.99
Horiz. Dispersion
(m)
0.137
0.037
0.061
0.045
Horiz. rms e- beam size
(µm)
402
59
100
77
Horiz. rms e- divergence
(µrad)
10.7
90
116
111
Vert. Beta Functions
(m)
2.52
2.73
34.9
34.9
Vert. rms e-beam size
(µm)
7.9
8.3
29.5
29.5
Vert rms e- divergence
(µrad)
3.2
3
0.85
0.85