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Roman Pots at LHC for TOTEM

This workshop discusses the requirements and constraints of using Roman Pots as detectors at the Large Hadron Collider (LHC) for the TOTEM experiment. Topics covered include the design of the Roman Pot detectors, cryogenic silicon sensors, mechanical integration, welding techniques, and impedance issues.

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Roman Pots at LHC for TOTEM

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  1. Xth Blois Workshop on Elastic and Diffractive Scattering Helsinki 23-27 June 2003 Roman Pots at LHC for TOTEM Marco Oriunno CERN, EP Division on behalf of the TOTEM Collaboration http://totem.web.cern.ch/Totem/ Xth Blois Workshop, Helsinki 23-27 June 2003

  2. TOTEM Layout ~150m ~215m Optical Theorem Xth Blois Workshop, Helsinki 23-27 June 2003

  3. Operating Scenario TOTEM needs special/independent short runs at high-b* (1100m) • high-b optics for precise measurement of the scattering angle • reduced number of bunches to avoid crossing angle Total reduction of ~10-5 Lnom= 1034 cm-2 s -1 LTOTEM ~ 1028 cm-2 s -1 Parallel-to-point focusing: Trajectories of proton scattered at the same angle Low Luminosity during TOTEM runs is due to technical operating conditions Xth Blois Workshop, Helsinki 23-27 June 2003

  4. Roman Pot Constraints/Requirements • LHC beam collimations : • Horizontal Plane > 10s (Asynchronous beam dump failure) • Vertical plane > 10s (Halo) • Secondary vacuum for detectors and cables (outgassing) • RF Shielding of detectors since high intensity bunched beam structure • Low X/Xo design for background and trigger related problems • Alignment • Mechanical Stability • Radiation environment for ancillary electronics LHC Constraints TOTEM Requirements Xth Blois Workshop, Helsinki 23-27 June 2003

  5. Edgeless Detector Edgeless Detector Thin Window Thin Window b* = 1100 m x = Leffq +vx0 Leff(m) v 10s 10s RP1+2 = 150m RP3+4=215m Xth Blois Workshop, Helsinki 23-27 June 2003

  6. Why Cryogenic Silicon for TOTEM • Very small edge effects as no guard ring is needed (small surface current). The inner edge of the sensor can be shaped to match the beam hole. • Good x,y resolution of ~ 10 mm • High radiation hardness due to freezing trapping of radiation defects (test have shown radiation resistance ~ 1015 n/cm2) Xth Blois Workshop, Helsinki 23-27 June 2003

  7. Pot TOTEM Requirements LHC Constraints Detectors Roman Pot “Payload” Bottom-Top Design approach : LHC construction launched, Roman Pots are still in design phase Roman Pot Mechanics Integration in the LHC environment Xth Blois Workshop, Helsinki 23-27 June 2003

  8. Conceptual Design of the Roman Pot detector CMS Tracker Hybrid 3cm Thermal analysis Xth Blois Workshop, Helsinki 23-27 June 2003

  9. Xth Blois Workshop, Helsinki 23-27 June 2003

  10. Welding on a flat foil and folding Xth Blois Workshop, Helsinki 23-27 June 2003

  11. PCB cards Cooling Connectors Flat cables D-Connector Flange with double side D-Connectors Flange with feeding through PCB cards Xth Blois Workshop, Helsinki 23-27 June 2003

  12. Xth Blois Workshop, Helsinki 23-27 June 2003

  13. Constraints from the LHC-Vacuum : • Since all the vacuum chamber in the LSS are NEG coated, the pot must be designed to stand a baked out up to 300oC • A risk analysis of the operation of the Roman Pot operation should be performed • A design pressure of at least 1.5 bar shall be considered in the design of the window. A rupture disk breaking at a differential pressure of <0.5 bars should be installed Xth Blois Workshop, Helsinki 23-27 June 2003

  14. Impedance Issues • LHC Impedance requirements impose small resistivity and small volumes: • when the Roman pots are closed to the beam in DAQ mode the estimated impedance is 0.1 mW and it is by far lower than impedance budget allowed for the machine 250 mW , assuming a pot in Steel. • Operation restriction for near-beam detectors: • Image Current -> heat deposited on the pot by ohmic heating • RF Fields -> noise induced on the detectors and the electronics • Both are related to LHC bunch structure: • for TOTEM special runs -> 36 bunches 1.95ms spaced Xth Blois Workshop, Helsinki 23-27 June 2003

  15. Image Current Heating1 Main assumption: the heat is deposited on the bottom surface of the pot since the thermal diffusion length is >> then the skin depth Energy deposited In both cases the temperature rising is negligible < 1oC due mainly to the smearing of the peak current Q along the beam length sz. one bunch striking the window produces a heat load due to ionization ( 0.4 10 11 protons per bunch) 1. X.E. Lin, D.H. Whittum, “Image current heating on a metal surface due to charged bunches”, Phys. Rev. ST, Accelerators and Beams, 3, 101001 (2000) Xth Blois Workshop, Helsinki 23-27 June 2003

  16. Density (Kg/m3) Young Modulus (GPa) Yield Strength (Mpa) Radiation length Xo (mm) Aluminum 6063 2800 72 250 89 Stainless Steel 316L 8000 200 280 17.6 Copper 8900 110 152 14.3 Beryllium IF-1 1900 303 300 350 Titanium 6AL4V 4700 110 1100 35.6 Inconel 718 7800 200 1050 17.6 Deformation (m) Thickness 0.1 mm Steel Load = 1 atm. 800mm 400mm stress (Pa) Max. 900MPa Xth Blois Workshop, Helsinki 23-27 June 2003

  17. Brazing Pot window Thin window Technology issues • Brazing: • Inconel looses ~30% of the strength • Low limit on the thickness of the joints • Brazing inside the pot -> dead space • Electro erosion: • Low Yield of material • Increase of Porosity • Bottom of the pot flat -> no dead space Both technologies are available at CERN Tests on prototypes ready to be performed Xth Blois Workshop, Helsinki 23-27 June 2003

  18. Prototyping and Test of the Pots at CERN (July 2003) • Brazing test on Folded Inconel Foils • Production of 5 pot prototypes to test under pressure TEST procedures • Cycling load 0bar/1bar -> no permanent deformations • Thermal test cycling from RT to 300oK with and without pressure load -> no permanent deformations • Increasing of the pressure till rupture to define the ultimate load • 1 Pot Prototype for RF Pick up test on electronics • Production of 1 mock-up of the pot with dummy detectors to have a full integration exercise with the services Xth Blois Workshop, Helsinki 23-27 June 2003

  19. What has been done for the Roman Pot System: • Two solutions have been designed: Symmetric distribution of the loads but less favorable access for maintenance Not symmetric loads but optimized access For Both solutions • A compensation system based on external vacuum pumps allows for a fine regulation, releasing the force on the pots • A capacitive system accounting the relative position of the top-bottom pots, • Integration of two Roman Pot stations between the TAN and D2 Xth Blois Workshop, Helsinki 23-27 June 2003

  20. Xth Blois Workshop, Helsinki 23-27 June 2003 Roman Pot Device (First Version)

  21. Compensation bellow Pot Lever Arm Capacitive sensor Roman Pot Device (Second Version) Xth Blois Workshop, Helsinki 23-27 June 2003

  22. Horizontal Roman Pot Station Measuring and cross-calibration purpose LHC Beams Xth Blois Workshop, Helsinki 23-27 June 2003

  23. QRL (LHC Cryogenic Line) 4m Xth Blois Workshop, Helsinki 23-27 June 2003

  24. Study of alternative solutions ( in progress) Xth Blois Workshop, Helsinki 23-27 June 2003

  25. Collimator QRL BPM TAN Racks Roman Pot Station (made of two RP devices) Xth Blois Workshop, Helsinki 23-27 June 2003

  26. Cryogenic Cooling of detectors • Two main options: local cooling or passive elements • Active local cooling system • Passive system : Heatpipes, Mass Conduction • Cold source at 80oK -> Commercial Pulse-Tube (no vibrations) • Other systems as Joule-Thompson nitrogen flow are under investigation • QRL transfer line of LHC machine = NO ! Heat loads ~12 watt/pot > 230oK 2 Watt few mWatt DT ~ 5oK Heatpipe ~ 1500mm DT ~ 20oK 130oK 80oK Xth Blois Workshop, Helsinki 23-27 June 2003 Pulse tube

  27. TOTEM Test Beam Read/Out Hybrid ~RT Liquid Nitrogen Reservoir (77oK) Kapton Pitch Adapter (Thermal bridge) Edgeless Detector (130oK) Vacuum Vessel Xth Blois Workshop, Helsinki 23-27 June 2003

  28. Trigger Timing of RP4 at 215m Xth Blois Workshop, Helsinki 23-27 June 2003

  29. Radiation background on the Roman Pot (D.Macina, N.Mokhov) Assumptions: • Simulation has been done from IP5 to Q7 (v. 6.4,  = 0.5 m) • Peak luminosity is L=1034 cm-2 s-1 • Absorbed dose is normalized to : 180 days, 24 hours per day, <L> = 0.5 · 1034 cm-2 s-1,equivalent to 6.22·1015 non-elastic events per year Results: Accumulated radiation dose around the RP is ~ 103 Gy/yr Annual Fluence of Hadrons on the tunnel ground~109cm-2 Radiation hard components (cooling, local triggers, power supplies…..) are required This results are still true for IP1 since almost identical to IP5 Xth Blois Workshop, Helsinki 23-27 June 2003

  30. Futures plans • Mechanical and EMC characterization of full prototypes of the Pot (CERN, summer 2003) • Optimization of the detectors package and choice of an operational temperature for the silicon (CERN, Test Beam 2003) • Choice of a Cryogenic cooling system for the detectors (CERN and ILK Dresden) • Risk analysis on the operation mode of the Roman Pots vs. LHC • Integration of services in the Tunnel vs. space allocations and radiation environment Xth Blois Workshop, Helsinki 23-27 June 2003

  31. Xth Blois Workshop, Helsinki 23-27 June 2003

  32. Roman Pots Project • CERN is developing Roman Pots for the TOTEM experiment in a common effort with EP and EST division • The design is performed according the requirements of the TOTEM experiment, which is an LHC approved experiment for total cross section and the elastic scattering on IP5 • The project is meant as an LHC technology, therefore worth for IP1 where the optics and the machine layout are almost symmetric to IP5 (provided a suitable DAQ/Trigger integration) Xth Blois Workshop, Helsinki 23-27 June 2003

  33. Design of the Roman Pot is focused on three main phases: • Design of the Pot • Design of the Roman Pot Station • Integration in the Tunnel • Main items: • Thin window : outgassing prevention and RF shielding • Mechanical Design of a thin window • Integration of detectors inside the pot: precision mounting, cooling • Design of flange to routing the detector’s services outside the pot Xth Blois Workshop, Helsinki 23-27 June 2003

  34. RF Fields (basic considerations) Magnetic field induced by the beam bunch structure are mainly tangential and propagate perpendicular to the window decaying exponentially according to skin depth parameter: The skin depth is given by For TOTEM special runs we have w = 0.4 MHz, and we have d = 660mm for Steel and d = 100mm for copper. A thin window of 150mm in Steel is not sufficient to shielding the electronics since one get only a reduction of 10% of the magnetic field. A thin coating of copper ~50mm gives already a reduction of exp-(50/10) =6.7x10-3 Further Developments A full EMC test is foreseen on a one of the prototype of Pot in order to quantify the RF pick up noise Xth Blois Workshop, Helsinki 23-27 June 2003

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