modified. A cavem in Point 1 has therefore about LEP-like dimensions in a longitudinal orientation, while for a perpendicular cavern larger diameters

avoid disturbance to LEP, these existing structures should not be OCR Output machine tunnels (LEP and SPS) and a service cavern for LEP (US 15). To ground which have to be taken into account. There are transfer and constructed. However, many structures exist already above and below conditions are good and large caverns and access shafts could be

Point 1 The beam line is at 79 m below ground level. The geological installation of an experiment in Point 3, because of the very difficult geological conditions.

three interaction regions 1, 5, and 7. No considerations have been made concerning the experiments. LHC experiments could, therefore, be housed in newly excavated caverns at the data with LEP at the even numbered points of the accelerator during the initial round of LHC The working group has assumed that the four large LEP experiments are still collecting of these eight areas.

sections of the accelerator. Consequently, experiments could in principle be conducted in each The lattice of LHC foresees crossings of the two proton beams in all eight straight

2. Site considerations

Volume 3 of the proceedings.

new experimental areas for LHC. More detailed description of specific subjects can be found in This report tries to summarize the overall concepts and boundary conditions concerning aspects of constructing, installing and operating an experiment at LHC.

to the presentations made in the detector instrumentation groups and concentrated on the various experimental areas. The discussions III the Detector Integration group have been a complement about future LHC experiments in order to propose realistic designs for the new LHC interconnected. The principal aim has been to collect a sufficient amount of basic information concentrated on problems where experimentation and machine design are closely The activities of the ECFA—LHC working group on Detector Integration have

1 . Introduction

·•··•··•··•··•=

P. Sonderegger, H. Taureg, A. Verdier, F. Wittgenstein.

L. Leistam (convener of working group), K. Potter, A. de Rujula, W. Scandale, Contributions: W. Bartel, L. Camilleri, G. Carboni, C. Fabjan, K. Eggert, A. Herve,

Lars Leistam, CERN

D9

275

pressure bumps in the presence of the beams. OCR Output

situ bakeout will also be needed to ensure the lowest possible residual gas pressure and avoid found for supports and vacuum getter pumps about every 2 m throughout the ·; 16 m. An in vacuum chamber can be equipped with a thin-walled central section. Space will have to be this subject, since the minimum aperture required by the machine is not known. If required, the chamber, a 2.5 cm central chamber was suggested. The working group could not conclude on diameter of 5 cm. Some arguments were presented in favour of a smaller diameter vacuum The room temperature vacuum chamber through the experiment will have a nominal standard pp interaction region is shown in Fig. 1.

completely clear region for physics experiments will not exceed : 16 m. An example layout of a With a minimum of space for vacuum pumps and valves, and maybe a correction magnet, the of small angle particles from the interaction region by a suitable absorber of about 3 m length.

will be about 30 cm closer. In addition, the coils of this magnet must be protected from the flux superconducting quadrupole, the physical end of the cryostat of approximately 1 m diameter The closest magnet is 20 m from the interaction point but, as it is a high gradient radioactivity in elements close to the beam pipe.

At these very high luminosities it is important to consider the resulting induced particles per bunch be increased to 3 >< 1011, but the beam line layout will remain the same.

interactions anywhere else), the bunch spacing must be increased to 45 ns and the number of To obtain the maximum luminosity (5 x 1034 cm·2 s·1) at one interaction point (i.e no to a pp luminosity range of 1.65 >< 1034 to 5.5 x 1032 cm‘2 s'

pp or ion-ion consists of a quadrupole triplet giving a 5* between 0.5 and 15 m, corresponding shift will be limited.The standard insertion for an LHC interaction region when operating with The proton beams will normally collide in only three areas as the total beam-beam tune 3 . Interaction region layout

needed, Points 1 and 7 should be used in preference to Point 5.

The working group concluded that in case only two new experimental areas would be territory and new land will have to be acquired.

access shafts and surface buildings will fall to a large extent on Swiss is, however, close to the border between France and Switzerland. The large diameter cavern can be envisaged. The interaction region at Point 7 geological conditions are similar to those of Point 1. The construction of a

Point 7 The beam line is located at 94 m below ground level and the m) is therefore excluded.

and is of inferior quality. The construction of a large diameter cavern (> 24 expensive. The molasse rock starts at a relatively large depth below ground making the construction of access shafts more complicated and more of water layers have to be traversed in order to reach the underground area,

Point 5 The beam line is located at 86 m below the surface. A number

up to 35 m are possible.

a longitudinal orientation, while for a perpendicular cavern larger diameters modified. A cavem in Point 1 has therefore about LEP-like dimensions in

276

277 OCR Output

to the assumption that both machines will operate alternately for a number of years after the The long-term physics program of LEP and the construction schedule for the LHC lead 5 . LEP/LHC alternate operations

50 m downstream.

To reduce backscattering, the synchrotron radiation will have to be absorbed on a dump some radiation as low as possible, taking into account the acceptance requirements of the experiment.

A careful gptimigatign of this bend will be necessary to keep the critical energy of the

experiment.

head-on collisions. This bend results in a synchrotron radiation fan, which will traverse the LHC beam 1.2 m higher. A further bend is needed at the entry to the experiment to provide LEP must be deflected vertically through an angle of about 6 mrad, in order to raise it to the region. The layout of such an interaction region was discussed in detail. The electron beam of In the ep mode of the LHC the two beams will collide in only one interaction 4 . ep interaction region

support structure (its movability !) prevents a more detailed appreciation.

experiments, but the absence of a mechanical design of the interaction quadrupoles and its It was generally agreed that the proposed standard interaction region is suitable for LHC

indicated.

longitudinally-orientated cavern. The LEP beam elements at a non—collision point are also Fig. 1 Layout of a standard LHC interaction region beam line in a

, _

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278 OCR Output

Fig. 2 Shielding arrangement for a LHC experiment during LEP operation.

‘{x\//{

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non trivial, a possible shielding arrangement for an LHC -shielding[access: shielding the LEP experiments in their garage position is

experiments:

constraints to the design of LHC experiments and necessitate some adaptation of the LEP be regarded as particularly difficult. Altemate LHC/LEP operation will indeed introduce some The working group recognizes that the question of altemate LHC/LEP operation must

the beam can pass through the beam pipe at the centre of the experiment.

3) The detector is lowered or raised to the beam line of the other machine, so that beam pass and to install shielding where necessary.

2) A sufficiently large passage is cleared through the detector, in order to let the 1) Experiments are rolled out of the interaction region into a garage position.

possible scenarios:

The difference of 1.20 m in elevation between the two accelerators leads to three

guaranteed during beam operations.

space requirements for shielding [1], if safe access to the experimental cavern has to be machine must allow the corresponding beams to pass. The problem is compounded by the During operation of one of the machines, the experiments associated with the other of the accelerators and for the experiments associated with them.

installation of the LHC has been completed. This altemate running has consequences for both

tentative listing of their installation regions. OCR Output

gas-jets, fixed targets or detecting the neutrinos/muons from the collision point. Table 2 gives a The working group took note of several presentations suggesting experiments using size and weight compared to the large "muon" experiments.

Presentations of ep and ion-ion experiments show that they do not differ significantly in is the difficulty of providing a good crane coverage over the experiments.

substantially bigger diameter perpendicular to the beam direction. Common to both orientations little or no more than LEP dimensions with the axis parallel to the beam or a cavern of The dimensions of these conceptual detectors suggest that one needs either a cavem of to 30,000 tons. The diameters transverse to the beam range from 15 to 25 m.

is about 2 to 3 times that of LEP experiments and the weight is expected to range from 10,000 The main difference with respect to the LEP experiments is the overall size. The length

L3 + 1 32 16 11'000

Muon toroid (coil) 22 ^{18 4‘100}

Shaped solenoid 28 ^{24 23'000}

Compact solenoid 33 ^{14 21'O00}

24 17

Iron toroid 25'000

length [ml diameter [ml weight [ton Detector Dimensions

Table 1 see Table 1.

preliminary survey of possible large detectors, designed to include a muon detection system, conceptual detector designs were presented during the workshop. The working group made a The design of LHC experiments is still in a very early phase, however, several 6 . Dimensions of experiments

-schedule: the change—over time will set a limit on the change—over frequency

intersections

·desigg: additional constraints due to difference between LEP and LHC

279

respect to the beam line. A 20 m diameter shaft, offset to the side of the cavern, serves as the OCR Output Fig. 3 shows the layout of a 35 m diameter hall in a perpendicular orientation with cavem and a longitudinal cavern.

indicated in Table 1, the working group has designed two experimental areas: a perpendicular Following the general civil-engineering considerations and the overall dimensions under good rock conditions.

deposits. Preliminary studies indicate that cavems with diameters up to 35 m can be excavated

depend on the properties of the molasse rock and the thickness of the covering moraine

time for the excavation in comparison with other techniques. However, the cavern dimensions surrounding the excavation to be employed as active support, which will minimize the cost and LEP experimental cavems, which have a diameter of 21 m. This method allows the rock mass The foreseen construction method will be identical to the one used for excavating the underground areas.

thickness.The depth and existing surface structures preclude a cut-and-fill construction of the situated in the molasse rock, which is covered by a layer of moraine deposits of variable The possible sites for the construction of the experimental caverns allow them to be 7 . New experimental cavems

studied in detail.

forward-region detector. In particular, the possible conflicts with machine installations must be or enlarged sections of the straight section tunnels will have to be arranged to accommodate a

‘muon" detectors. Special cavems will have to be constructed far from the intersection regions Here the influence on the design of the experimental areas is very different to the large u·beams (deflected) "side" cavern

Neutrino-e, pt (from collision point) special cavem at ~ 500 m in present tunnel

Neutrino·tau (from collision point) in straight section, limited size detector; would tit Beauty detector intersection, forward regions up to about 20 m Fixed target in straight section, enlargement of present tunnel Gas-jet in straight section, enlargement of present tunnel

Tvpe Regions

Table 2 LEP.

layout and it is therefore possible that some equipment must be removed during the operation of from collision point. There are no such corresponding free regions in the LEP straight section layout: a 29 m gap starting 60 m away from collision point and a 99 m gap starting 118 m away The LHC lattice leaves two larger equipment-free regions in the standard straight section

282 OCR Output

limited to monorails or possibly arc-shaped cranes with maximum capacities of 35 to 40 tons.

of conventional bridge cranes in the cavems. Crane installations over the experiments will be the initial design phase. Furthermore the size ofthe experiments will not allow the installation the experiment and space in underground areas and surface buildings must be allocated during gas-distribution, communications, etc. Some of these installations constitute an integral part of service and support installations: electrical power, cables, cooling and ventilation, cryogenics,

In general the next generation of large experiments will require sophisticated and bulky

is 1.23% and in Point 7 it is 0.72%.

experimental hall at an angle compared to the horizontal floor. In Points l and 5, the inclination

Because of the inclined construction of the LEP/LHC tunnel, the beam line traverses the

along the beam line will require careful access control and monitoring during shutdowns.

experimental hall during the operation of the accelerator. In addition, the induced radioactivity adequate shielding around LHC experiments, such as to allow permanent access to the Independent of the orientation of the cavern, it will be essentially impossible to arrange envisaged.

and fixed target experiments, for which modest enlargements of the machine tunnel can be accommodate very particular detector arrangements, such as small angle spectrometers, gas—jet It is also conceivable to construct a cavern with a different geometry in order to

area.

Point 5. Consequently, only a LEP size cavern, as shown in Fig. 5, can be constructed in this As mentioned in Section 2, the construction of a large diameter cavem is not possible in experimental hall.

installed in a second cavern placed at a radiation safe distance (8 m of rock) from the moving large detector parts to the surface. Counting rooms and service installations would be a very large or heavy experiment. The garage position is here replaced by the possibility of large 18 m diameter access shafts placed directly over the beamline to facilitate the assembly of beam position is more difficult than in the perpendicular layout. The cavern shown has two difficult. A parallel garage hall can be built, but the transfer of detector parts from garage to axial (along the beam) opening of the experiment. The arrangement of a "garage" is, however, limited by civil engineering constraints. The 24 m diameter hall shown allows a convenient A longitudinal orientation as shown in Fig. 4 makes better use of the hall diameter during installation.

access space, garage position, free loading space in front of the access shaft and storage space is justified by the space needed for a 20 m diameter experiment: space in the beam position, underground halls. The overall length of the hall, shown as an example, is 100 m. This length will be provided in order to fulfil the basic safety requirements concerning access to counting rooms and service installations for the experiment. A second independent access shaft situated in the shielded extension of the experimental hall. This shielded hall will also house the sides of the cavern at floor level. Personnel reach the cavern through a 9.10 m diameter shaft OCR Outputmain equipment access shaft. Small tunnels for personnel access and safety run along both

which one could be equipped with a 2500-ton lift (shown at Point 1 but adaptable for 5 and 7). OCR Output Fig. 4 A 24 rn diameter longitudinal cavern with two 18 m access shafts, of

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few large sections or as a complete assembly. A possible installation scenario is shown in Fig.

public roads to the experimental site. The detector is then rolled to the beam line position in a position the experiments are assembled from relatively small parts which can be transported on be assembled with similar techniques to those used for the LEP experiments. In the garage be made available nearly two years in advance of the first beam. In this case the experiment can If the underground area incorporates a garage position for the experiment this area can i) Perpendicular cavem with garage position.

Two scenarios can be envisaged:

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the surface buildings. The tentative planning is shown in Fig. 6.

of the detector, the civil engineering schedule for the underground cavern and the availability of The installation procedure of an LHC experiment will be determined by the construction OCR Output8 . Installation of experiments

286 OCR Output

possible to judge whether this installation time is adequate.

for the experiments. However, with the present knowledge of future LHC experiments, it is not The working group recognized the effort to accommodate a sufficient installation period large experiments to meet the overall schedule.

public roads. Therefore sufficient surface hall and lab space must be provided, in order to allow superconducting coil, may exceed the dimensions and weight which can be transported on The size of the LHC experiments is such that indivisible components, eg a large Fig. 8.

of lowering several thousand tons at a time [2]. An example of an installed detector is shown in detector components andthe access shafts have to be equipped with heavy lifting gear, capable The surface area has therefore to provide sufficiently large halls for the preassembly of the large units are subsequently lowered into the experimental cavern and assembled on the beam line.

preassembled into a few large components at the surface of the experimental site. These heavy installation procedure has to take this into account. The experiment should therefore be later than in case i), because of the presence of the LEP shielding. The detector design and A longitudinal cavern will be available for the installation of its experiment somewhat ii) Longitudinal cavern without garage position

Fig. 7 Installation procedure in a cavern with garage position.

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REFERENCES

# * # * ik

presented designs should be regarded as a starting point for future work on experimental areas.

set "natural" limits to the work performed by the Detector Integration Working Group and the Finally, it must be stressed that the absence of more definite LHC detector designs has regarding new experimental areas for LHC.

scheduling of LEP/LHC alternate operation, plays an important role in the considerations We also note that the overall installation schedule for the LHC project, including the

experiments.

experimentation. However, more work remains to be done on the installation of large the basic features of the proposed experimental areas and interaction regions are suitable for We have examined the various conceptual detectors proposed for the LHC and find that

9. Conclusions

Fig. 8 Large detector installed in a longitudinal cavem.

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