Experimental Area Meeting V. Bobillier1 Good connection to earth (in many points) of every metallic parts to be installed in the cavern is very important for safety reasons. Nevertheless, even if it is related, this will not be the main subject to be discussed today. We see that there should not be big conflict between EMC and earthing safety rules. EMC (Electro-Magnetic Compatibility) plays a key role in all small or large electric and electronics installation. Noise problems (level) can be reduced quite well when EMC rules are respected. For detectors, signals (that sometimes are of the order of magnitude of a few [nA]) that must be readout by the electronics are very sensitive to noise. Ground equipotentiality in the cavern is important (for both, safety and EMC). Particularly since we will have some signals transported on copper lines from detector to counting house. (This even if the signals are differentially transmitted through shielded cables.) Why grounding (and EMC in general) is important in HEP experiments.

Experimental Area Meeting V. Bobillier2 Grounding scheme in the experimental cavern Top view To surface Mains transformer It is foreseen to consider all the metallic structures connected to earth as a grounding mesh from the experiment point of view.

Experimental Area Meeting V. Bobillier3 Side view Grounding scheme in the experimental cavern Beam pipe It is foreseen to consider all the metallic structures connected to earth as a grounding mesh from the experiment point of view.

Experimental Area Meeting V. Bobillier4 Grounding scheme in the counting house. The metallic structure in the false floor of the barracks will be connected in many points to the cooling pipes, the cable trays and the earth cables running under the racks. This will be connected to earth and considered as a grounding mesh where all racks will be connected via a connecting braid. Grounding in the barrack’s false floor. Grounding of the racks.

Experimental Area Meeting V. Bobillier5 Grounding of the detectors: All data transmissions between the detectors and the counting house (about 100 meters) are made through optical links (except for the VELO). Floating HV and LV power supplies located either in the counting house or in the cavern with connection to ground on the detector side will be used by all detectors. Every sub-detector is connected individually to ground on one point either through the support rails, the 120mm2 earth cables or on the “earth connection plates” on the cavern walls. This connection has to be as short as possible. LHCb has less accessibility problems than the other experiments. This gives flexibility to make some additional inter-connections from detectors to ground if the base line solution shows to be ineffective.

Experimental Area Meeting V. Bobillier6 Detectors Vertex Locator: The Vertex Locator (VELO) and its electronics has the disadvantage of being located inside the LHC machine beam pipe, where the induced noise from the LHC machine will be important. The grounding of the VELO and its link with the machine ground is foreseen to be a challenging issue. The analog data transmission from the VELO to the counting house (~ 70 meters) will be made through differential copper lines. (Major worry) The VELO uses an analog readout with a powerful DSP based common mode compensation to resolve possible problems.

Experimental Area Meeting V. Bobillier7 Detectors Rich 1 and Rich 2: The Rich is binary but its discriminators are located in a well shielded and controlled environment inside the HPD vacuum tubes (on the detector). The proximity of the magnet and especially its power lines might be an additional source of noise. The data transmission from the front-end electronics of this detector are made via optical fiber ribbon cables.

Experimental Area Meeting V. Bobillier8 Detectors Silicone Tracker : The Silicone Tracker (Inner Tracker and Trigger Tracker) is also close to the magnet and its power lines. It uses an analog readout with a powerful DSP baseline compensation. The Silicone Tracker has long Kapton cables transporting the analog detector signals to the on- detector service boxes. A double faraday cage is used for the detector boxes. The data transmission is also made via optical fiber ribbon cables.

Experimental Area Meeting V. Bobillier9 Detectors Outer Tracker : The Outer Tracker detector is also pretty close to the magnet. This binary detector uses long detection wires that act as antennas but the shielded tube around the wires can be considered as a first protection in addition to the double faraday cage. Data are also transmitted via optical links.

Experimental Area Meeting V. Bobillier10 Detectors Muon: Calorimeter: The Muon is binary. The iron blocks forming the Muon filters will have a good shielding effect. It will have to be ensured that those blocks are well interconnected to ground. Here also, the data transmission is made via optical fiber ribbon cables. The Calorimeter has sensitive analog outputs but the large amount of iron forming this detector will play the role of a good and effective shield. Here also, the data transmission is made via optical fiber ribbon cables.

Experimental Area Meeting V. Bobillier11 Detectors Muon iron filters: The iron blocks forming the Muon filters will have a good shielding effect. It will have to be ensured that those blocks are well interconnected to ground. To ground via the shortest way.

Experimental Area Meeting V. Bobillier12 UPS TDM cupboards EXD panel Transformer Locations of the power distribution components in the experimental cavern Diesel generator at surface UPS Diesel generator How these main network components will be connected to earth ? It is not precisely known yet!TN-S Can the transformer be shared between the F-E electronics and the CPU farm ?

Experimental Area Meeting V. Bobillier13 Open questions What will be the best way to connect the faraday cage of the detectors to the ground and where should it be connected to ? (To the detector ground, to the cavern ground or somewhere else) (problems to make a good connection with aluminum components…?) How can one be sure that the reinforcement structure in the concrete is well connected to ground ? What is the most effective way to connect the cable shields and where ? (to the detector’s structure, to the front-end electronics’ ground, to the faraday cage…) Can the transformer be shared between the F-E electronics and the CPU farm ? A document about grounding, shielding and LV distribution in LHCb is available here (still a draft version, to be finalized soon): On the web a page concerns grounding:

Experimental Area Meeting V. Bobillier14 Installation and organization questions What will be done by who ? TS-EL usually install the earth cable around the cavern and in their cable trays. But who will do this for detectors cable trays ? Who will make the installation of the earth cables to connect the metallic structures to earth ? Who will make the installation of the interconnecting braids in the false floor of the barrack ? Time schedule, Planning ? Other questions ?

Experimental Area Meeting V. Bobillier15 Annexes… A ground cable well connected to the ground in many points running all along each cable tray is very efficient. It reduced the size of the ground loop cross- section which is good to reduce the sensitivity of it.