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Background and the Interaction Region Design

In order to see where the background comes from, the beam line from the exit of main linear accelerator(linac) to the interaction point(IP) is shown in Fig.2 for JLC-I(tex2html_wrap_inline1435500GeV). [2] A bending magnet of +20mrad, which is the so-called big bend, is needed because the background from the upstream linac can not directly hit a detector. The second bending magnet of -16mrad makes a horizontal crossing of tex2html_wrap_inline1577mrad between two beams at IP. There are two major sections of 1200m collimation and a 600m final focus system in the beam line, where (1)muons and (2)synchrotron radiation are produced, respectively. At IP, (3)tex2html_wrap_inline1399 pairs and (4)minijets are created in beam-beam interactions. In the subsequent sections these four kinds of background are briefly discussed together with the possible designs of an interaction region against them.

Figure 2: Top view of the beam line from the exit of the main linac to the interaction point (IP) of JLC-I(tex2html_wrap_inline1435500GeV).

Toshiaki Tauchi
Fri, Dec 20, 1996 02:24:05 PM