WHAT IS NEW AT CERN?

Transcription

1 WHAT IS NEW AT CERN? Dominique Missiaen, Antje Behrens, Patrick Bestmann, Jean-Frédéric Fuchs, Jean- Christophe Gayde, Mark Jones, Hélène Mainaud Durand, Antonio Marin, Dirk Mergelkuhl, Mateusz Sosin, CERN, Geneva, Switzerland Abstract Since 2009, the LHC has running very well and this year reached an energy of 4TEV, producing more luminosity than expected. At the end of 2011 the LHC experiments Atlas and CMS had both accumulated 5 fb-1. This has left very little time to access the tunnels and accomplish survey campaigns, except for some repositioning of the low beta quadrupoles and a measurement of sector 78 which has been a very unstable area since the era of LEP. From the end of 2012 up to November 2014, a long shut down will take place in order to repair the splices in the LHC interconnections, allowing in the future an energy of 7 TEV. This period will be used by the survey team to remeasure all the components of the LHC in the vertical and horizontal directions. The LHC collimator train also completed its first measurements during the last winter technical stop and studies for a new LHC survey train have been started. The Linac4 project, future proton source for the LHC injectors, is progressing slowly but work has been done for the fiducialisation of components and the determination of the geodetic network necessary for the installation of the infrastructure in the tunnel. The HIE-Isolde project has provided the opportunity to study a permanent monitoring system using the BCAM technology. This paper will present the status of all these activities and studies as well as the strategy for the survey activities during the next long shut-down. INTRODUCTION While the LHC and the injectors are running, the survey team is working on the alignment of new projects such as linac4, HIE-Isolde and the preparatory work for the LHC experiments upgrades planned for the next long shut-down and the non-lhc experiments. Studies have also started concerning the possibility of realising the automatic survey of LHC arcs and several sensors have been tested. During the technical stops of 2 months at the end of each year, an access is possible in the tunnels allowing preventative survey in the unstable areas and the first measurements with the train for the survey of the LHC collimators. A long shut-down of almost two years, called Long shut down 1 (LS1), has been scheduled to repair the splices in the LHC interconnects and this period will be used by the survey team to maintain the vertical and horizontal alignment of the whole LHC components and its injectors chain and to consolidate the low β quadrupoles permanent monitoring system. The survey team will also be deeply involved in important upgrades of the LHC Experiments such as the change of beam pipes for ATLAS, CMS and LHCb or new detector parts installations in ALICE and others. This will lead to a full opening of the detectors and a huge demand of survey measurements. LHC ACTIVITIES Survey and realignment Since 2009, the LHC runs very well with a maximum of time dedicated to physics. The schedule only allows some access in the tunnel during a winter technical stop which takes place at the end of each year and lasts about two months. Figure 1 : vertical smoothing in The sector 78 of the LHC, which has been detected very unstable since the era of the LEP has been remeasured in the vertical plane during the technical stop of and the well known hole of the LHC has been realigned as show on figure 1. The same measurement has been done during the last technical stop in in vertical and in horizontal as the LHC is critical in both planes and has not been measured in H since In the vertical direction, the hole was not observed with the direct levelling done with the DNA03 and Na2 and no re-alignment was done. But a deep analysis of the data taken with the AT401 [1] showed that the hole reappeared this year as well. In the horizontal plane, despite the fact that the magnets were re-aligned many times in vertical since 2009, there was no major displacement of the magnets. A total of 38 magnets that were far away from the smooth curve by more than 0.25

2 mm were realigned, among those only two were at almost 1 mm [1]. The LHC collimators survey train For the first time during the technical stop , the train for the remote survey of collimators [2] was tested in the Long Straight Section 7 measuring 200 m of collimators on each part of the IP7. The same measurements using standard techniques such as direct levelling and ecartometry were also realized allowing a comparison between both methods. In the horizontal plane, the remote measurements taken with the train are very similar with the standard ones as shown on Figure 2. In the vertical plane, some geoid corrections have still to be implemented in the final calculation. The main movements observed on these magnets are in the vertical plane where the Q1s are sinking while the Q3s are going in the opposite direction. This is particularly visible in points 1 and 5 where a new cavern has been built for the LHC experiments as shown on Figure 3. There were no real request from the Physics and Operation for realignments but the main goal for the survey team was to have these magnets in a smooth position with respect to the experiments on one hand and the magnets located in the Long Straight Sections on the other hand. During the realignment of the Q2 located on the right side of point 5 where a radial displacement of 25 μm was requested, we had the surprise to observe, thanks to our permanent monitoring system, the displacement of this cryo-magnet by 0.8 mm in the horizontal direction and mm in the vertical. This phenomenon is due to the fact that there are too many constraints in the interconnections between the magnets mainly due to tie rods which prevent the cryostat to move longitudinally the ones w.r.t the others and to bumpers which prevent the triplet to move towards the experiment. Figure 2 : horizontal position of collimators This test was globally very promising while some improvements concerning communication and software have been decided and already undertaken. The next step will be the measurements of the same zone and the collimators around point 3 during the LS1. Repositioning of the low β quadrupoles Despite the fact that the repositioning of the low β quadrupoles can be done remotely and doesn t require an access in the tunnel, a repositioning of these critical magnets took place during the technical stop for the points 2 (Alice) and 8 (LHCb) and during the one of for the magnets located around points 1 (Atlas) and 5 (CMS). CRYOSTAT JACK SENSOR + HARDENED INTERFACE WASHERS ACTUATOR Figure 4 : load sensors - strain gauge (washer type) As a matter of fact the cryostats were not supported only by their jacks but also by the interconnections themselves. This problem triggered the decision to install load sensors (Figure 4) between the jacks and the cryostats. These sensors will measure the weight applied by the cryostat on each jack and will help the survey operator to take the right action during a realignment operation. The installation has started in 2012 and will be completed during the LS1 [3][4]. Figure 3 : vertical position of the low β quads around IP5

3 Train studies LHC STUDIES The pre-studies for a new train generation have already started based on the experiences with the collimator survey train. The most delicate and complicated part of the train is the stretched wire reference which is used also in the vertical plane. This requires a very precise knowledge about the wire parameters and a wellcontrolled environment. It is impossible to ensure this for larger parts of the LHC and a new concept for the vertical measurements has to be developed. First tests have shown that the Ultrasonic HLS gives very promising results for a mobile application on the train. This system can be used to determine the height difference between two mobile parts of the train. The link with the magnets is done again using digital close range photogrammetry which worked very well already on the collimator train. The mobile HLS application is a compromise between the micrometric precision which can be achieved by these systems and the rough train conditions in which it will be implemented. The temperature gradients inside the flexible water tubes and the stabilisation of the water surface are limiting the HLS performance but it is still possible to achieve the precision of an optical level. The concept for the radial measurements has slightly changed as well. Instead of using optical laser micrometers around the wire, the new concept is working with photogrammetry only. Technically it is possible to measure the wire position directly with photogrammetry but the environment must be well under control. First tests done on several types of wire (Figure 5) gave results better than 30 µm in the determination of position. Figure 5 : different types of wire (iron, fishing, carbon peek and vectran) detected by photogrammetry Depth of scene, background, contrast and illumination are parameters playing an essential role for the precision and reliability of such a system and not all parameters can be fully controlled in the LHC. Major developments have to be done in order to make this reliable and fully automatic. Mechanically the most important modification will be the use of modular robotic arms for the manipulation of the sensor heads and wire anchorage. This arm is manipulating already the existing sensors for tests with excellent precision and great results so far. LINAC4 LINAC4As first step of the LHC luminosity upgrade program CERN is building a new 160 MeV H linear accelerator (Figure 6), Linac4, to replace the 50 MeV Linac2 as injector to the PS Booster (PSB). PIMS CCDTL DTL chopper line 160 MeV 104 MeV 50 MeV 3 MeV 86 m Figure 6 : Linac4 layout Installation of the machine infrastructure has been progressing since the delivery by the civil engineering company of the Linac4 building and tunnel at end All equipment has been preliminarily integrated into an extensive 3-D computer model which allowed an early solution of interference problems. The infrastructure installation will be completed in September 2012, to leave place to the installation of machine components. The beam line and assembly reference points were marked on the ground tunnel and a scan of the installed infrastructure in both the surface building and the tunnel was undertaken. Network determination During the Xmas Break 2011/2012 a new determination of the underground geodetic reference network along the main LINAC tunnel and the transfer line tunnel has been accomplished using AT401 and Gyromat3000 measurements. The new coordinates in the CCS (CERN Coordinate System) of the survey reference targets in the tunnel floor of the L4 have been determined by a final calculation with constraints on the reference marks of the Booster. The removable survey pillars will be soon installed and added to the L4 network. Everything is ready for the jack installation that has started in September (source, LEBT, RFQ, MEBT) and should be completed for all the L4 machine components in the beginning of The 3 MeV test stand The section up to 3 MeV is being installed and commissioned in a dedicated test stand. The LEBT is in place and the RFQ, built entirely in the CERN Workshop, has been installed and will be aligned soon. The first diagnostic line should be installed in a few months. All the 3 MeV elements will be transferred and aligned in 2013 to their locations in the Linac4 tunnel. Fiducialisation A complete metrology measurement of the first CCDTL module (Figure 7) has been done in Russia (BINP, Novosibirsk) in June with an API laser tracker in order to check feasibility of the 6 ½ tanks assembly and the geometry of the axis composed by the 6 drift tubes. RFQ

4 Figure 7 : metrological check of the first CCDTL The first DTL and CCDTL modules should be delivered in few months at CERN and many metrology measurements will be necessary with laser tracker before tunnel alignment. Beam commissioning of the linac4 will take place in steps of increasing energy between 2013 and From end of 2014 Linac4 could deliver 50 MeV protons in case of Linac2 failure. HIE-ISOLDE The HIE ISOLDE project is a major upgrade of the ISOLDE REX facility. The goal is to increase the energy and quality of the radioactive ion beams delivered to the experiments. The beams will be accelerated in a superconducting linac made of 6 cryo-modules (Figure 8) containing superconductive RF cavities and solenoids. The cryo-modules will share the insulation vacuum with the beam vacuum. The system is mainly based on well-proved elements such as the Brandeis CCD Angle Monitor (BCAM) devices [7]. The key elements such as the viewports and the possible target types have been studied and tested in different environments, including the constraints due to vacuum or cryogenic conditions. A HBCAM camera which is an upgrade of the proved BCAM is under development. Implementation of a new CCD, mechanical adaptation changes, focal length upgrade to increase the field of view and integration of an illumination ring are foreseen. First steps are encouraging and no important problem is expected. The software development [8] is well advanced. The mathematical model and main software modules for the reference frame reconstruction are ready. The validation started successfully on a partial but almost full size mockup. The HIE-Isolde Alignment System technological options are now almost all fixed. The goal is to be ready to install the first alignment system once the first cryomodule will be assembled and ready for vacuum and cryogenic tests. In the meantime more standard survey is being prepared to cover the needs of the cryomodule assembly in a class 5 clean room on The survey infrastructure integration in the global layout is under study. Simultaneously, preparatory work for the linac prealignment, the transfer line installation and alignment is on-going. Beam commissioning at 5.5MeV/u is foreseen for the end of the 2014 run and physics for the start of Two additional high-beta cryomodules will be installed in The two low-beta cryomodules completing the linac are foreseen for a later stage after ACTIVITIES FORESEEN DURING LS1 The LHC and its injectors Figure 8 : The HIE-ISOLDE Linac To run the linac in the optimum conditions an integrated permanent alignment system [6], based on opto-electronic sensors, optics and precise mechanical elements, is being developed. It aims to guaranty positioning and monitoring of the cryo-module active elements with precisions of 0.3 mm for the RF cavities and 0.15 mm for the solenoids at one sigma level along directions perpendicular to the beam axis. The concept is to create a permanently controlled reference frame in which the fiducial marks of the active elements will be observed. Figure 9 : the LHC and the injectors chain Initially foreseen to repair the splices of the LHC interconnects in order to run the machine at 7 TEV, the LS1 has been scheduled for a period of 20 months starting at the end of Taking into account that the next long shut down (LS2) is scheduled in 2018, many services decided to organize a heavy maintenance of their

5 equipment not only in the LHC but also in the injectors chain (Figure 9). The survey team, in close collaboration with the Accelerator & Beam Physics and Operation groups decided to launch a huge campaign of survey and realignment which includes: - The PS Ring which was surveyed for the last time in The PS Booster, surveyed in 2008, which will be renovated to be a central link in the chain of the new injector system when the Linac4 will be connected - The FT16(TT2) and TT10 transfer lines providing particles to the SPS - The SPS, surveyed for the last time in the H plane in 2005 and where a hole of 4mm on a distance of 1 km has to be realigned in V - The TI2 and TI8 transfer lines linking the SPS to the LHC which are well known as unstable areas since their construction - The LHC, not measured since 2008, where some areas are very unstable like the sector 78 and where the degradation of the alignment in the H plane reaches 0.12 mm per year at 1σ, which means that, in a period of 10 years, 2 magnets per sector will be misaligned w.r.t their neighbors by more than a mm if no realignment is done during LS1. Maintenance of the low β quadrupoles alignment system Low beta quadrupoles in the LHC are equipped with Hydrostatic Levelling Sensors (HLS) and Wire Positioning Sensors (WPS) in order to monitor their position. The simplest solution to check that all the HLS sensors work well is to add or remove water to the hydraulic network through a filling/purging device and check that all the sensors see the same displacement. Concerning WPS sensors, the stretched wire is displaced radially and vertically at its extremities, and the sensors have to monitor displacements that are proportional to their longitudinal position along the wire. Till now, this operation could be carried out directly in the tunnel, but the area will become more and more radioactive. Devices that will allow performing remotely these tests are under development. Figure 10 : WPS filling-up system The remote filling/purging for HLS will consist of a mobile water tank connected to the water network (see Figure 10). The vertical displacement of the tank is performed along a worm by a DC motor coupled with a RVDT [9]. Speed reducers and ending contacts complement the system. Figure 4 presents the prototype that is under validation at CERN. For the WPS, the principle of this system is to push the wire thanks to a piston tilted at 45 w.r.t the local vertical so that the validation can be done for both vertical and horizontal readings of sensors. Figure 11 : WPS validation system The concept of pushing the wire was validated with the system shown on Figure 11: the wire has been pushed more than 4000 times by the piston, without breaking. A period of 10s after displacement was necessary to stabilize the wire before recording the readings of the sensors [5]. Two systems based on the concept of displacing the wire are under design. LHC Experiments During the next LS1 an important amount of work is planned in the four LHC experiments in order to consolidate the infrastructure, to repair or fix known problems, install detector part which have been staged and install components of the first upgrade. Among these activities the change of the central beam pipes of ATLAS and CMS will be done as well as the replacement of the long section of the LHCb beryllium pipe. Different detector installations will be done such as the ATLAS IBL inner detector insertion near to the IP, the installation of the YE4 yoke end cap disk in CMS and of new detector modules in ALICE. For that, the full opening of the detectors is foreseen. These activities lead to a strong participation of the survey team not only during the LS1 period but already now in the frame of the preparatory work which is done for months mainly during the LHC run periods. As an example, a 20m long scale one mock-up of the ATLAS central part has been built to test the tools and the procedures in this area. In parallel the CMS YE4 preassembly has been performed on surface. Another example is the preparation of the LHCb large dipole consolidation for which a control of the deformations and displacements of the coils in the yoke between the 0 and 1 Tesla conditions was demanded. After study and tests photogrammetric measurements have been successfully done in this unusual environment, the camera being exposed to magnetic field of about 200 mt.

6 In the meantime the integration of an automatic system based on BCAMs for opening/closing of ATLAS is being studied in collaboration with the ATLAS team. The radioprotection and the integration of the ALARA (As Low As Reasonably Achievable) rules is also one of the concerns leading to some methodology and hardware changes. For example the use of AT401 instead of total stations or the integration of alignment systems in shielding parts will help in this direction. Resources This very ambitious survey campaign will require, on top of the 21 staff members, 15 extra persons coming from the manpower contract to realize all the measurements and re-alignments. A large effort of the Experiment Collaborations and Physics Department is also done to support the survey for experiments. A very detailed planning is in the process of being established taking into account the general LHC planning and all the co-activities constraints. The preparation concerned also the hardware maintenance of the CERN home-made instruments- and the software field data acquisition, post-processing and database. [5] S. Mico, Déplacement du fil par électro-aimant, edms n , CERN, [6] J-C. Gayde, G. Kautzmann et al, HIE Isolde Alignment and Monitoring System Technical Design and Project Status, Fermilab, Batavia, September [7] BCAM Brandeis Camera Angle Monitor, [8] J-C. Gayde, G. Kautzmann et al, The HIE-ISOLDE Alignment and Monitoring System Software and Test Mock-up, Fermilab, Batavia, September [9] A. Bonnal, Pilotage d'un moteur à courant continu pour contrôler le fonctionnement d'un ensemble de capteurs hydrostatiques et pour le remplissage et la vidange d'un réservoir d'eau Rapport de stage, july 2012, EDMS CONCLUSIONS Despite the fact that the LHC and the injectors chain has run very well since the restarting in November 2009 and there were very few access in the tunnels, the activity of the survey team was rather important. It mainly focused on the alignment and fiducialisation of new projects such as Linac4 and on R & D studies dedicated to a survey train for the remote measurements in the LHC and the permanent monitoring of superconducting RF cavities and solenoids located in the tank modules of the HIE-Isolde using the BCAM technology. In the experiments, out of the intensive Technical Stops periods, the work was focused on LS1 preparatory work and Non- LHC experiment projects. The LS1, which has been carefully and heavily prepared, will be a more intense period in terms of survey activities in the tunnel and all the studies will be slowed down and restarted in In the meantime and almost independently of the LHC schedule, the survey work for Non-LHC experiments will have to be continued. REFERENCES [1] D. Missiaen, M. Duquenne, Could the laser tracker AT401 replace digital levelling and ecartometry for the smoothing and realignment of the LHC, IWAA12, Fermilab, Batavia, September [2] P. Bestmann and al, The LHC collimator survey train, IWAA10, DESY, Hamburg, September [3] M.Sosin, Installation of load sensors at Low quadrupoles supports, CERN EDMS , December 2011 [4] M.Sosin, J.Sandomierski, Installation of load sensors at P5 low-beta jacks, CERN EDMS , June 2012