SL-Note-99-019 (EA)

Geneva, Switzerland

15 February, 1999

In a few years from now, the TI2 transfer line for proton injection from the SPS into the LHC has to be installed. Before that time, starting at the end of the year 2000, civil engineering work for the TI2 tunnel has to start, in particular the connection with the TCC6 primary target zone in the West Area. The trajectory of the TI2 transfer line would traverse the shielding of the T1 primary target itself. Therefore this target has to be moved out of the way. Both the transfer line towards the T1 target, as well as the H3 beam that serves the West Area test beams with secondary particles produced in T1, have to be adapted to the new position. In this note we outline the work that has to be done, its implications, as well as cost estimates and a planning.

The T1 target has to be moved downstream by approximately 12 metres and sideways by about 1.5 metres as indicated in figure 1. Its exact co-ordinates are listed in the appended Beatch outputs.

At the end of the 1997/1998 shutdown (18-02-98), the induced radioactivity levels around T1 were measured by TIS/RP and levels up to 90 mSv/h were found at the exit of T1, in between the shielding and the pair of MTR dipole magnets following the target. In view of this it was decided to leave the target shielding in place for cool-down till the installation of the TI2 line, to order new shielding and to reuse only the ‘active’ elements (target box, monitors) of the target. The target box will be reused without changes, while for the instrumentation (TBIU/TBID) one considers the possible replacement of the Aluminium foils by Titanium ones.

After a few more years of cool-down, only the part of the shielding that blocks the passage of the TI2 line will be removed and some local shielding plates or concrete blocks will be installed to protect the surroundings against radiation from the inside of the shielding.

Note that a quadrupole of the transfer line to the new T1 target passes just next to the target shielding. It has been verified that the quadrupole just fits with about 10 cm margin.

As a first step of the work in 1999/2000, a 80 cm thick concrete shielding wall will be erected at the downstream end of T1, before any other work in TCC6 starts, to reduce radiation doses for the personnel working in the area. The new target shielding has been ordered at a cost of 154 kCHF. Delivery has been promised November 1999. A test mounting will be done in the lab. Final mounting in TCC6 should therefore take place in the second half of January 2000. The zone around the new T1 location will be cleaned out and prepared in the first half of January.

The tubing of the T1 cooling system and the transfer line has to be modified. The cost of these modifications have only been estimated very roughly and a more precise estimate will come later.

The jib-crane (‘potence’), which serves to install and take out the target box and instrumentation, can be installed on the upstream side of the new T1 target as to minimise interference with the cable tray and other infrastructure above the target. The height of the cable tray has then to be increased locally by some 5 cm and some bus bars and neon tubes have to be slightly displaced. As an alternative solution, the SL-BT group will study the construction of a new tooling, more convenient, safer to operate (reduced radiation exposure and risk of electrical shock and mechanical hazards for the personnel) and adapted to the new environment. The cost of new tooling remains to be estimated.

The dismantling of the old target (in » 2004) and the installation of the new target is supervised by specialists in SL/BT (S.Péraire). The dismantling of the old target will require the use of the shielded Clarks of the Transport group.

Note that the old T1 shielding is on the straight path of the transfer line in case of failure of the bends. It can therefore serve as part of the shielding system for such cases without constructing additional dumps, at least until the target shielding is partly removed and TI2 is installed.

The new transfer line has been designed by A.Hilaire. It contains no more wobbling magnets, as there is no space available for them, due to the interference with magnets in the line towards T9, which will not be dismantled in time.

The loss of the wobbling station is not a real problem, as the H1 beam (towards the Omega spectrometer) has been dismantled in 1997 and therefore only a single secondary beam line is served from the T1 target. One single restriction in the operation of the H3 beam is introduced by the absence of wobbling: it will no longer be possible to run pure electron beams by converting photons from decay of p^o’s produced in the target. This option, only interesting up to about 150 GeV/c (at higher momenta, one can separate the electrons in the secondary beam from the hadrons by synchrotron radiation), has in reality never been used. Tertiary electron beams produced from a -120 GeV/c direct secondary beam through Bremsstrahlung in a thin Lead target are in fact very pure and give adequate fluxes for test beams. The suppression of the wobbling station eases of course the operation (no more WOBSU surveillance programme required).

The installation of the transfer line will be launched by SL/BT and is discussed with SL/MR and the equipment groups involved. The magnets are available. Some are powered in alternation with magnets in the TI2 line by means of a high-power switch. In case the cabling for the T9 line can not be used, the cabling for the switch (after the shutdown of Lep) will cost approximately 20 kCHF.

At present two MTR magnets, some 13 metres of helium tank and two TAX-type mobile dumps immediately follow the target. Above the target and the beam line there are many cables, that need to be protected from radiation. Hence a massive side and top shielding. To allow rapid intervention in case of breakdowns, in a zone without cranes and with very restricted space, special mechanisms were installed to temporarily remove parts of the shielding in a fast and semi-automatic way. Unfortunately these mechanisms will no longer be compatible with the new layout due to lack of lateral space. Therefore a new system has been designed by Michel Clément, which will fit in the new location. A schematic view of this system is shown in Figure 2. A test mounting is planned to happen in November 1999 in building182, as agreed with EP Division.

Only the vacuum tube and one small quadrupole (about 500 kg) of the TI2 line will interfere in case of (hopefully rare) breakdowns of one of the MTR magnets. In such cases the TI2 quadrupole and the vacuum tube will have to be removed temporarily during the intervention.

Secondly, the TAX will be replaced by fixed dumps of TCX type, not motorised, with a single hole of diameter 64 mm centred on the beam axis. The choice of TCX is now justified, as

• The H3 will never be operated as a primary beam (its top momentum is 250 GeV/c, i.e. well below the momentum at which the SPS is operated), hence is single large hole is sufficient.
• The protons that traversed the target are dumped cleanly in the TCX, anyway.
• The absence of movement makes the mechanics much simpler and more robust, thus reducing the risk of exposure of personnel to high radiation levels (cf. recent incident on H4 TAX).
• One would have to buy new TAX blocks anyway (position of holes w.r.t. blocks is different), which are much more expensive than TCX blocks (where some are available already).

The thickness of the TCX along the beam can be the same as for two TAX modules (3.2 metres). The problem of muon fluxes through the dump can be avoided by requiring the T1 target head to be in position OUT (as part of the interlock conditions for access to TT61). Note that for primary beam momenta below 400 GeV/c, the maximum strength of the MTRs is such that an external bend limitation would be required to avoid the risk of primary particles traversing the hole in the dump.

In between the MTR and the TCX a 600 mm diameter vacuum tube will be installed. Inside the MTR magnets there will be no vacuum.

The changes in this region are under SL/EA responsibility.

4. The modifications to the H3 secondary beam

The secondary beam leaving the T1 target station towards the West Area leads to a splitter station located some 600 metres downstream of the primary target. From there two branches transport the secondary particles to two secondary targets from which the X5 and X7 beams are produced. These beams, serving a vigorous test programme of the LHC collaborations and many smaller groups, have recently been upgraded to a top beam momentum of 250 GeV/c. We propose to modify the H3 beam in such a way that it joins up with the existing splitters, while keeping its main characteristics in terms of transmission and optical behaviour.

The approach is to displace most of the beam sideways in the tunnel by roughly 1.38 metres. Due to the change of height in the transfer line, the beam height of the H3 in the tunnel will increase by about 15 millimetres. The 30 metres long matching section in between the horizontal bend following the TCX and the first vertical bend, so far consisting of 5 quadrupoles, will be shortened by 12 metres. As the top momentum of the H3 beam is now only 250 GeV/c, compared to 400 GeV/c in the past, this can be achieved with 3 quadrupoles only and without significantly changing the beam characteristics at the exit of this section.

At the top of the tunnel, there are now two groups of (essentially vertical) 5 MBE-type dipoles each. To connect the beam to the existing X5/X7 splitters, the outer 4 MBE’s of each group will be tilted and the central ones replaced by 2 horizontal MCB magnets each. This requires two additional power supplies for the MCB’s, one for each group of two. Those power supplies are available. However, due to the tilt angle the required current in the MBE magnets increases to 4 kAmps, thus requiring a reinforcement of their power cables. Those extra cables have been installed already in 1998. No changes are required downstream of the splitter. Please find added in Appendix A the Beatch description of the new beam line. In figure 3 we show the different modifications to the H3 beam schematically.

This part of the project is under SL/EA responsibility.

Along the second group of MBE magnets, there is a concrete wall, that separates the tunnel TT61 from the splitter zone TT4 (the old West Area target zone). In fact this wall has a function in supporting the roof, which carries 4 metres of earth on top of it. The wall has to be removed over a length of 6 metres to make space for one of the MBE magnets. Adequate supports are added to reinforce the surrounding structures. Over an additional length of 8 metres, a 35 cm diameter hole has to be traverse the wall at a skew angle to allow the passage of a vacuum tube. ST Division has prepared this and work has been advanced to the 1998/1999 shutdown in order to avoid interference with the activities in TT61 and TCC6 the year after. This work was completed on 12 February 1999.

In the tunnel, TT61, the beam is moved from the South to the North side of the tunnel. Although it eases somewhat the access to TCC6 via the tunnel, all services are now available on the wrong side of the tunnel.

For the cooling water, we try to recuperate as much of the existing material as possible. In the primary target area and in the first 110 metres long section of the H3 beam# beam, the water tube (supplied with water from BA6) will be moved from the South to the North side. In the last 200 metres long section of the tunnel, before the entrance to TT4, the old tubing (from before the H1+H3 upgrade to 400 GeV/c) is still available on the North side of the tunnel. A total of 2x7 valves will be mounted in the inlet pipe to allow cooling of the magnets in this part of the beam. For the intermediate section of the H3 beam (positions 120 to 458) the cooling water and will be done from the South side via flexible tubes to be installed over the top of the tunnel. This work is supervised by ST Division (R.Mollay, A.Monsted) for the fixed tubing.

SL/MS takes care of flexible tubes and also of the power cables, which will traverse the tunnel along the roof. This work involves a total of 35x2 man-days plus 5kCHF materials.

5. Other aspects

Access of personnel to TCC6 is most convenient via BA7. There is one lift for personnel (13 persons) and one for materials (capacity 25 tons). At the time of writing the ambient dose at the passage was of up to almost 100 mSv/hr, but this can be reduced to acceptable levels (40 mSv/hr) by temporarily removing 3 magnets in the T9 line: QTLD660500, QTLD660600 and in particular MPLV660604. The door separating TCC6 and TNC (BA7) would have to be opened and the passage into the neutrino cave locked for the duration of the work. For convenient passage of material the shielding at the exit of TCC6 on the T9 line has to be removed temporarily. Instead some shielding will be installed in a location inside TNC. Temporary storage of equipment between dismounting and reinstallation in a new position can be done in the BA7 zone, further downstream in the neutrino cave. For this purpose a surface of 25x2 m² (with handling facilities) is required for 11 magnets and an additional 60 m² surface with >1.6 metres height for the temporary storage of ³  650 tons of steel blocks and 20 steel bars.

The section of the line towards T9 in the region between the old T1 position and the exit of TCC6 has to be temporarily removed, in order to make space for manipulation of other equipment in the work area. In fact it was announced that the CHAMONIX workshop that the neutrino beam from T9 will no longer be required and therefore its reinstallation can be postponed.

The access doors in TT61 have to be slightly modified, mainly to change the position for beam passage. The TCC6 ventilation door has to be moved somewhat and the TCC6/TNC door has to be temporarily dismounted. Total cost estimated to be about 30 kCHF.

Some amount of obsolete radioactive material has to be stored for possible future re-use, requiring 40 m² of space for 6 dipoles and 3 quadrupoles plus, at a later stage, 15 m² for the target shielding blocks. In addition some material can be eliminated, namely 16 TAX blocks, 4 TAX tables, 4 chariots, a 12 metres long vacuum tank (90 cm diameter) with support structure, 4 magnet supports and some jacks, which would occupy a total surface of 60 m². This will be discussed with M.Silari (TIS/RP).

The TI2 ventilation and the civil engineering work for TI2 will be done in the 2000/2001 shutdown. For that purpose a few H3 elements will have to be temporarily removed, but this is not in the scope of this note.

The cost of the displacement of T1 and its implications has been estimated. A break-up is listed in Table 1. The new target shielding and the civil engineering in the TT4/TT61 zone have already been paid. The total cost of the project is 1393 kCHF, excluding new tooling for interventions on the T1 monitors or target box which is under study in SL-BT and which is expected not to exceed 50 kCHF.

A planning has been prepared jointly by J.Montes in AC/TCP) and M.Clément with P.Pierre (SL/EA). It is appended as Table 2. An up-to-date version is available on the WWW.

M.Clément (SL/EA) has kindly agreed to do the technical co-ordination of the activities in TCC6 and the surrounding areas during the shutdown 1999/2000.

Table 1 : Cost estimate

Table 2: Provisional planning by J.Montes (AC/TCP) with input from P.Pierre and M.Clément (SL/EA)

Figure 1: New layout in TCC6 (PDF) (PS)

Figure 2: Schematic design of mobile support structures for MTR magnets and shielding in TCC6 (PDF) (PS) .

Figure 3: Overview of modifications to the H3 beam

Addendum: Beatch of the new H3 beam

Addendum: Beatch of the new transfer line towards T1