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7.3 Layout

IP layout is shown in Fig.7.7. Nearest final quadrupole magnet (QC1) is located at 2m from IP, where the QC1 is shielded against a solenoid field of 2 Tesla by a superconducting compensation magnet.
  
Figure 7.7: Interaction region.
\epsfxsize=13cm \epsfbox{detir/interaction.region.eps}

A huge number of X rays, which are created in electromagnetic showers of $e^{\pm}$ pairs at QC1, are absorbed in conical and cylindrical tungsten masks. Angular coverage of the conical mask ranges from 0.15 to 0.2 radian, leaving a small dead cone angle, but the front part of the conical mask could be instrumented as a calorimeter. There is the luminosity monitor covering an angular region between 0.05 and 0.15 radian inside the mask. The carbon mask in front of the QC1 is very effective to absorb low energy back-scattered electrons. The 4-layer vertex detector (VTX) is located at radial distance from 2.4 to 6.0cm, followed by an intermediate tracker to link charged tracks between the central drift chamber (CDC) and the VTX. All these instruments are installed in a support tube of 80cm diameter[10].

The interaction region has been updated since the 1st ACFA-LC (Beijing) workshop[11] in order to further reduce $e^{\pm}$ pair backgrounds in VTX and CDC, especially X-rays in the CDC. The major changes are in the beam pipes and the locations of the carbon mask and the pair monitor. The beam pipe inside the VTX is made of 0.5mm thick beryllium, 4cm in diameter, while the major part is a 15cm diameter beam pipe of 2mm thick aluminum in the mask. These two beam pipes are connected with a conical beryllium pipe of 2mm thickness. The 15 cm diameter is large enough for $e^{\pm}$ pair particles to curl inside the beam pipe without interactions. The pair monitors consisting of active pixel device are now located at 176cm from IP, i.e. inside of luminosity monitor. In the previous design, they were closer to IP and were one of the sources of X rays.


next up previous contents
Next: 7.4 Estimation of background Up: 7. Interaction Region Previous: 7.2.3 e+e- pairs
ACFA Linear Collider Working Group
E-Mail:acfareport@acfahep.kek.jp