Physical Foundations for Design of High Energy Beam Absorbers

We analyzed the physical basics for design of absorbers for high energy beams of electrons and photons. Typical examples are the collimators and dump systems. In particular, we considered a collimator for usage in Cornell ERL project, where it could be used for reduction of γ , − e halo, minimization of exposure SRF module to SR from neighboring bending magnet and for absorption of direct beam hit in case of emergency. The collimator proposed uses Pyrolithic Graphite (PG) at front end and Tungsten insertion closer to the exit end. Beam dump system for absorption of 15 MeV, 1.5MW average power also uses a PG. As examples we considered gamma collimator and gamma absorber (dump) for ILC positron conversion systems also. 1. OVERVIEW Collimator is an inevitable component of any high-power electro-optical system. ILC and ERL are the most prominent examples of this kind. ERL uses for recirculation of electrons: two DC SRF modules linked with CESR by electro-optical channel and by return loop at the other side [1]. Beam from injector module (~15 MeV) is directed into the first SRF module, which accelerates the electrons from 15 MeV to 2.5GeV. At the same time, the beam of 5 GeV, arriving from CESR site, transfers its energy into the same SRF module by deceleration to -2.5 GeV. After passage the ~180 deg return loop at the end of North SRF module, two beams (separated longitudinally by half wavelength) enter the second (south) SRF module. In this module, one beam continues its acceleration to 5 GeV, meanwhile the other beam continues its deceleration reaching ~10MeV. After that this low energy beam is separated from the highenergy one and directed into the beam dump, while the other beam, having energy ~5 GeV and low-emittance, goes to the experimental area and further to the CESR loop. After making a turn in CESR and channels, the beam enters the North SRF module and the process is repeated. One place for the installation of a collimator could be identified at the entrance of the second (south) SRF accelerating section of ERL after the turning arc. One additional collimator of the same design-type (with complementary fast kicker in front of it) should be installed at the entrance of North linac. Another collimator (same design, but shorter) could be located nearby the Demerger. The same type of collimator(s) could be used for protection of low –aperture SR insertion devices. The arguments for this are straightforward. To some extent, there is no self balanced mechanism of equalizing energies at the exit of North linac to 2.5GeV (and to 5GeV in experimental area) like it is in a cyclic machine with auto-phasing. The only parameter in hand is the controllable RF power from additional RF generators which makes the energy of one beam