6 Design and Principles of Synchrotrons and Circular Colliders
261
Fig. 6.32 Synchrotron radiation emitted during beam separation in the HERA interaction region.
The plot shows schematically the interaction region lattice, the beam dimension and the direction
and density of the synchrotron light
emitted photons. For the HERA collider this problem has been studied in detail (see
Fig. 6.32) and a combination of absorbers and movable collimation masks have been
used to avoid hits from direct or back scattered photons into the detector parts.
The performance limitations of such an e-p-collider are given by the singe bunch
intensity of the protons (limited by the particle source), the overall current of the
electrons (limited by RF power or beam instabilities), the number of bunches that
can be stored in the machine (limited by technical reasons of the injection elements)
and the usual limits of the mini beta insertions that have been mentioned above.
The main parameters of HERA are summarised in Table 6.1:
Table 6.1 Summary of the
main parameters of HERA
Electrons
Protons
Energy
27.5 GeV
920 GeV
Beam current
58 mA
140 mA
Particles per bunch
4 × 10 10
1 × 10 11
Number of bunches
189
180
Beta function at IP x/y 0.63 m/0.26 m 2.45 m/0.18 m
Hor. emittance
20 nm
5.1 nm
Emittance ratio ε y /ε x
0.18
1.0
Beam size (IP) σ x /σ y
112/30 μm
112/30 μm
Luminosity
7 × 10 31 cm −2 s −1