Minutes of the 11th LHC Insertions Upgrade Working Group held on 6th March 2008
Present: F. Cerutti, S. Chemli, P. Fessia, M. Karppinen, N. Kos, J.-P. Koutchouk, H. Mainaud Durand, M. Mauri, K.H. Meß, Y. Muttoni, D. Nisbet, R. Ostojic, H. Prin, V. Parma, R. Van Weelderen.
Excused: O. Brüning, S. Fartoukh, M. Giovannozzi, F. Zimmermann
Invited: F. Butin, R. Veness
1. News and approval of the minutes of the last meeting
The minutes of the last meeting are approved without any comments
Ranko Ostojic recalled the reasons that led to the decision for the choice of a resistive D1 in the IR1 and IR5 (see slides). He recalled that in the LHC Conceptual Design Report from 1995 ("Yellow book"), the D1 and D2 are superconducting magnets powered in series, and identical in terms of strength and aperture (85 mm, based on outer layer of the LHC main dipole). The energy deposition studies made at CERN with this layout in 1994 showed that the critical areas were located on the non IP side of D1 and Q1. These were confirmed by the Fermilab studies in 1995. The change in the type of D1 (introduction of 6 resistive magnets instead of a superconducting magnet) was made in the LHC V5.0. It was based on the fact that the only available D1 superconducting separation dipole available at the time was the 80 mm RHIC magnet (D1 in IR2 and IR8). The aperture of this magnet was too small with respect to energy deposition limits. In addition, a Q4 magnet was introduced in this version, sitting in the same cryostat as the D2. Hence, the distance between the D1 and D2 doubled, allowing the use of normal conducting magnets. Finally, this choice also allowed doubling the lifetime of the magnets in strong radiation field.
Ranko concluded that the present situation is similar to that of 1997: the position of the D2 depends on the optimal position of the Q4, which has yet to be fixed and may allow using normal conducting magnets for D1. The decision also depends on the energy deposition results and on the plans for using the space between D1 and D2 for other equipment.
2. Plans for experimental vacuum chambers and Q1-TAS area in IP1/IP5 (R. Veness, ppt file)
Ray first gave a general overview of the vacuum layout in the IR1 and IR5 between the two sector valves in front of Q1, which is subdivided in three major areas symmetric around the IP: the experimental beam-pipes that are closed by remote flanges in front of the TAS, the TAS which extends from 19 to 21.130 m and the VAX zones. The last two areas are identical in ATLAS and CMS; however, the beam-pipes are significantly different.
The ATLAS experimental beam-pipe is composed of a central section with an ID58 mm surrounded by two sets of three vacuum chambers with gradually increasing ID, to 80mm and then to 120 mm with conical transitions. At the two extremities, the experimental beam-pipe is terminated with a module providing the transition from ID120 mm to the TAS beam-pipe ID of 34 mm, and a connection to a pumping station. As presently known, ATLAS plans to modify the central section in the future to less than ID58 mm, needed for the new central detector.
The CMS experimental beam-pipe has a central section made of Beryllium and stainless steel with an ID58 mm. It is surrounded with conical beam-pipes with increasing diameter up to 320 mm. These conical beam-pipes reduce in the area of the TOTEM experiment to ID55 mm, followed by a transition of 80/100 mm. The extremities are equipped with modules identical to those in ATLAS. The future plans concern the replacement of the CT2 chamber when TOTEM is removed, and probably the replacement of the central chamber for LHC luminosity upgrade.
The required changes for the triplet upgrade concern in both cases the redesign of the connections to the TAS. This is currently done with the pumping modules that are fixed on a remotely handled flange. An aperture increase of the TAS beam-pipe implies a new transition to ensure the connection of the experimental beam-pipe to the TAS beam-pipe diameter. The machine-experiment interface at 19 m from the IP should still be respected, although Ray considers that it could be discussed keeping in mind the available space to open the detectors, the ergonomics in front of the TAS and the fact that additional shielding may be added (the radiation dose in this area is around 50mS per hour).
Ray also recalled that the two TAS in ATLAS are 20 to 30 mm further away from the IP due to the as-built shielding position. A NC was closed with the mention "use as is" but the TAS could be brought back in place.
The "VAX zone" is a crowded area inside the shielding. The internal surface of the shielding will become significantly activated after a few years of machine running. The removal of this equipment is not mandatory to uninstall the Q1, but Ray remarked that it would make life considerably easier. He estimated that about 100 mm of longitudinal space could be gained in this area by suppressing one of the bellows around the BPMW.
Ray mentioned that the TAS body could be kept for the triplet upgrade, replacing only the copper beam-pipe that presently has Ø34/60 mm, and that could be replaced with a beam-pipe Ø55/60 mm using a better grade copper for mechanical stability. For accessing the beam-pipe, the TAS has to be removed from the shielding and opened as shown by F. Butin. François said that the TAS body should not be reused due to its activation and a reasonable cost of a new one. Ray mentioned that the TAS components that have presently inner diameters between 60 and 63 mm could be standardized to 80 mm if this could reduce their activation.
3. Present situation and plans for TAS in IP1/IP5 (F. Butin, ppt file)
François gave a brief description of the TAS, which is a 2.13 m long, 3.2 ton copper cylinder with a diameter of 500 mm. He then showed a series of pictures illustrating the TAS position in the shielding and the way that it was assembled and installed. The TAS sits in its 6 tons cast iron cradle acting as a surrounding shield which slides on two rails inside the 122 tons cast iron monobloc. The monobloc is centered with a conical junction and bolted to the cast iron fixed tube sitting inside the cavern concrete; it is supported by outer shielding rings that are bolted to the cavern wall. Any changes of this 375 tons shielding would probably be an issue. The alignment of the TAS is performed through the monobloc via 2+2 rods in the horizontal and vertical planes. The final alignment will be done once all ATLAS shielding is in place. H. Mainaud Durand confirmed that the alignment accuracy will be inside the range of ±0.3 mm.
François presented the removal procedure of the TAS. This delicate operation could last less than a week after the preparatory actions are completed (removal of the ATLAS big wheel, the support structure put in place and the beam-pipe disconnected). He pointed out that an impact study and a level of activation assessment need to be integrated in the removal procedure. The possible use of remote handling for some bolting operations on the IP side has already been studied and tried-out with good precision.
Ranko asked whether a cooling circuit was mounted on the TAS cylinder. The answer is yes, there are cooling tubes through the yoke but they are not connected to a cooling station. Ray remarked that heaters are mounted on the TAS body for beam-pipe bake-out.
Ranko asked if there is a possibility to move the Q1 supporting system. François commented that the jacks could eventually be fixed directly to the monobloc but he stressed that the cast iron would be hard to machine.
The present situation and plans for the TAS in IP5 will be presented in the next meeting
S. Fartoukh, R. Ostojic and H. Prin