THE DISPLACEMENT OF THE T1 TARGET

In order to make space for the passage of a transfer line for the injection of protons into the Large Hadron Collider (LHC), the West Area primary target T1 will have to be displaced. This work will take place in the winter shutdown 2000/2001 or possibly already in 1999/2000. Due to the presence of bending magnets in the line towards the neutrino target T9, which (for the moment) has to stay in place, the target will have to be moved downstream by about 12 metres and sideways by about 1.56 metres. The wobbling magnets upstream of the target will have to disappear for lack of longitudinal space. Some pictures of the implications of the TI2 transfer line on the West Area are available here (thanks to P.Collier/SL-OP).

If the neutrino line would not have to be preserved, the target could move upstream to roughly its old longitudinal position and the wobbling station could be preserved. However, the wobbling station is of limited use only, since the H1 secondary beamline has been dismantled. The only option lost due to the suppression of the wobbling station is that of pure electron beams (up to some 150 GeV/c) from conversion of photons from pi0 decays.

As a consequence of the displacement of T1, the H3 beam, which serves as parent beam for the West Area test beams X5 and X7, will be displaced sideways to the Gex side of the tunnel TT61. Schematically the whole project can be pictured as follows:

In the present design of the new H3 beam, the layout of the front end, up to the TAX, is exactly preserved. The only exception is the centering of the TAX blocks with respect to the beam axis. In fact, in the absence of a wobbling station, the impact of the primary proton beam (450 GeV/c) is a unique function of the H3 momentum:

In the case of high positive momenta, the proton impact is rather close to the beam passage. But even for the maximum H3 momentum of 250 GeV/c there is more than 30 mm of material between the proton impact and the edge of the bigest imaginable hole.
For this purpose we have shown the present large hole in the H3 TAX, 85 by 52 mm racetrack. In the absence of a wobbling station, a much smaller hole would be sufficient to cover all options.
From the above graph, one can easily see that the protons will always hit the TAX block sufficiently far away from its edges, provided the holes for the beam passage are positioned about 25 cm from the Gex side of the blocks.
See the sketch below for an explanation.

In fact the TAX will be replaced by a fixed collimator, a so-called TCX. To reduce radiation levels at the exit of the TCX during access to the tunnel, the T1 target head will be included in the H3tunnel chain (T1+B2+B3 in the old H3 terminology).

Downstream of the TCX, the acceptance defining section has to be shortened by about 12 metres. From then on the optics and layout of the beam line can remain unchanged till the top end of the tunnel TT61. The old Bends 3 and 4, that provided a 80 mrad (essentially) vertical bend, can be arranged such that (without longitudinal displacements) the beam can be made to arrive at the entrance of the splitters in exactly the same position and at the same angle as before. For this purpose, 4 out of the 5 dipoles in each group are tilted. The central dipole will be installed horizontally and powered separately. This way one preserves independent control over the beam steering in the horizontal and vertical plane and one clears the access to TT61 as quickly as possible. However, it requires a displacement of the wall opposite the entrance gate PPGX TT5.3. Note that the tilted dipoles remain of MBE type, whereas the central ones will be groups of two MCA's each. This preserves the present H3 acceptance to within some 5 percent, whereas horizontal MBE magnets (52 cm vertical aperture) would reduce the flux by 25-30% (for wide open COLL-4).

The relevant documents (present and preliminary status) are the following:

Beatch	h3for2000
Transport	h3for2000
Turtle	h3newt1

in usual places in the /afs/cern.ch/user/e/eagroup/database directory. A drawing of the optics exists as a Postscript file or in PDF format.

A note describing the whole project is in preparation. The present draft is available here.