Dump lines

For E89-009, the real photons were directly stopped at the Hall C dump and the primary electron beam bent by the splitter was transported and dumped at a temporarily installed 15 kW local dump. This arrangement was possible because beam current was limited to only 2 $\mu$A. In the case of E01-011, the beam current will be increased to 30 $\mu$A and the beam power will exceed the capacity of the local dump. Therefore, primary beam should be re-oriented back to the Hall C regular dump. Figure 38 shows the layout of the required new dump lines. The target vacuum chamber will be equipped with two exit lines, one for straight forward real photons and the other for bent primary electrons. The splitter magnet bends the beam by 8.15 degrees with respect to the central Z-line of Hall C, for example. The existing BZ magnet with a 1.5'' gap will be the first magnet located 5 meters away from the target. The second BZ magnet can be placed only 10 meters from the target in pathlength, since the first one bends the beam by 16.5 degrees. The second one has a 2.2'' gap and it bands the beam by another 8.35 degrees to guide the beam straight to the Hall C dump along the Z direction. If the beam energy is significantly different from the scheduled momentum (1.851 GeV), the BZ bending power should be increased. However, the bending powers (integrated magnetic field) of these existing BZ magnets meet just the requirement for 1.851 GeV beam, therefore, the beam energy cannot exceed 102% of 1.851 GeV. Due to BZ magnets' limited gap sizes, the path length between target and BZ magnets was minimized. It also reduces the radiation budget associated with the neutrons produced by beam halo on the dump line pipe. It might be better to use a rectangular shaped pipe for the electron line due to the small horizontal spread by the Splitter magnet. The photon and electron lines will be merged at a common chamber placed in the the second BZ magnet. Large diameter pipe will be used after the second BZ magnet. During the E89-009 experiment, four small beam line corrector magnets, two vertical and two horizontal, were used for the electron line to be transported to the local dump. Similarly, these four magnets can be used and installed between the target chamber and the first BZ or between the two BZs. They will serve to transport the beam correctly to the Hall C dump, it is important particularly in the vertical direction. The Splitter magnet cannot be used to change the primary electron beam direction since it fixes the optics for HKS and Enge Split-pole.

Fast rastered beam will be used for the calibration run with the CH$_2$ target to protect the target, however the experiment requires the point beam for the standard operation as mentioned above to achieve a high resolution. In order to protect the Hall C dump, the slow dump line raster should be installed between two BZ magnets.