|CERN AC Note (2000-03)-General description of the CNGS Project|
|2. Description of the CNGS project|
|Figure 9: Dipoles (red) and quadrupoles (blue) in SPS tunnel|
|The TN4 transfer tunnel will be used to orient the proton beam so that even
before it reaches the target it is already aimed at the Gran Sasso. This involves a
horizontal deflection of 33 degrees and a vertical deflection of 3.2 degrees after the
protons leave the SPS. The total length of the proton beam is 825 metres.
73 dipoles (bending magnets) and 28 quadrupoles (focussing magnets) will be needed to equip the TN4 line. All the magnets are of the same type as those used in the SPS (c.f. Figure 9 on page 15 ). These elements will only be powered for a very short period, while the protons are transferred towards the CNGS target, i.e. every six seconds or more; thus, they do not consume much electricity. The electricity power supply of line TN4 will be the same as that of transfer line TI8, at present under construction, which will link the SPS to the LHC.
2.2.2 The target and secondary beam
The CNGS target will consist of a series of small graphite cylinders. The size of the target has been chosen so that it will provide as many secondary particles as possible. In addition, the graphite cylinders must absorb the great heat and thermo-mechanical shock due to the energy deposited by the proton beam. The target must therefore be cooled with a jet of high-pressure helium gas in a closed circuit (helium is an inert, low density gas).