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Design of a high power synchrotron radiation absorber for HERA

In the framework of the HERA Luminosity Upgrade Project it is foreseen to move the final focus quadrupole magnets of the proton machine 16 m closer to the interaction region. As the electrons must not be affected by these magnets, the beam pipes for electrons and protons have to be well separated at these magnets. This implies rather sharp bends with bending radii down to 360 m for the electron orbit in the interaction region. At an electron energy of 30 GeV and a beam current of 58 mA these bends cause a high level of synchrotron radiation. The synchrotron radiation will be guided through the interaction region and will be absorbed far downstream at low power densities. However, it is unavoidable to stop parts of the synchrotron radiation beam at high linear power densities of up to 2 kW/cm rather close to the interaction point where the electron and proton vacuum systems are separated. In order to protect the proton final focus magnet and the septum beam pipe from this synchrotron radiation, a high power synchrotron radiation absorber was designed. This absorber not only has to withstand the heat load of the synchrotron radiation, but it also has to be designed to minimize the backward scattering of the radiation, because these scattered photons might hit sensitive detector components in the interaction region. This paper will first give an overview of the geometry of the interaction region with special emphasis on the synchrotron radiation. Then the geometrical and thermal requirements for the high power absorber will be described and finally the layout of the absorber will be presented.