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Fast gas Cherenkov Luminosity Monitor Progress Update

Fast gas Cherenkov Luminosity Monitor Progress Update. O. Atramentov, J.Hauptman. Iowa State University. NLC requirements on performance. The NLC design luminosity places rather tight constraints on the performance of NLC detectors:.

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Fast gas Cherenkov Luminosity Monitor Progress Update

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  1. Fast gas Cherenkov Luminosity MonitorProgress Update O. Atramentov, J.Hauptman Iowa State University O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  2. NLC requirements on performance The NLC design luminosity places rather tight constraints on the performance of NLC detectors: …bunch-to-bunch time interval of 1.4ns suggests almost speed-of-light response… …large background of low energye±, suggests a detector with a 10-20MeV energy threshold …large IR radiation dose will radioactivate the detector mass, suggesting an energy threshold above8 MeV …large radiation dose will damage detector components, requiring radiation-hard detector O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  3. Gas Cherenkov calorimeter satisfies these four requirements: • The Cherenkov photon signal exits the calorimeter volume at the velocity of light • Gas has index of refraction n = 1+, ( 10-3), therefore Cherenkov angle is small and energy threshold for electrons is high • Decay products from radioactivation of the calorimeter mass are below Ethand therefore invisible • A calorimeter made wholly of gas and metal cannot be damaged by any dose of radiation. O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  4. e- Calorimeter design • The Cherenkov light is generated by shower particles that cross gas gaps between absorber elements. • Shower particles co-move with the Cherenkov light as two overlapped pancakes. The width of these pancakes is about 10 ps. • Inside surfaces must be highly reflective at grazing incidence. O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  5. production of Cherenkov photons by 10 GeV electron transversing 2mm gas conduits in Pb. O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  6. Geometry Generic geometry – transverse segmentation of the absorber Example geometries: • “Spagetti” • “Honey-Comb” • “Cylindrical Lasagna” O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  7. Geometry: “Cylindrical Lasagna” Y Z X O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  8. Geometry: Hexagonal Array O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  9. Simulation Seemingly trivial: the higher the better, butalas: close to 100% reflectivity is notoriously hard to achieve (especially in UV) • index of refraction • reflectivity • absorber material • geometric parameters: • characteristic size of the light guides, • gas/absorber ratio Energy resolution critically depends on these parameters. We need a detailed detector simulation O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  10. Simulation Change of reflectivity from 100% to 90% reduces # of photons by a factor of two. Rohit Nambyar O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  11. Simulation We would like to have gas with the highest possible n. Watch, however, for resident light from scintillation! β-butylene( n=1.00131 NTP ) might be a better candidate (than alkanes): scintillation/Cherenkov~10-5 Rohit Nambyar O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  12. Simulation Conversion from number of photons to energy seems to be independent on the energy of incoming electron. Time spread ~ 11ps! Rohit Nambyar O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  13. Optical Surfaces … high reflectivityis not trivial – such detector requires a large area of high quality surface. Such reflectivity (~95%) can be achieved with a very smooth surfaces coated with Al. O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  14. Optical Surfaces Technique for obtaining optical quality of the metallic surfaces is well underway: polishing machine is built; surface roughness ≤30nm; reflectivity at grazing angles down to 200nm is coming (being fine tuned). Reference mirror, glass substrate. Polished stainless steel shim (Ukraine). O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  15. 1.4ns Pulser …tests DAQ’s response to the bunch-to-bunch interactions and optical system. Requirements: • train of several 20-50ps wide pulses; • every 1.4 ns; • Cherenkov spectrum; • table-top. Oesa Walker O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  16. Cherenkov Light Generation ~5 mm • Aluminized tube with lead “plug” at bottom Hexane (ρ~1, UV) ~1-2 cm • 1mm diameter hole in plug allows only electrons with correct direction to pass Pb • Upper portion of tube filled with hexane to generate and transmit Cherenkov light 90Sr Oesa Walker O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  17. Delay Design 1 • Use lens to focus light from generator into beam • Two beam-splitters break beam into three parts • Path lengths differ by 1.4ns (approx. 42 cm) Oesa Walker O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  18. Delay Design 2 • Connect 3 liquid light guides of differing lengths to end of generator tube • Lengths differ by 1.4ns (approx. 30cm in light guide liquid) • Coil light guides to ensure light emerges from same distance from PMT Oesa Walker O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  19. Summary & To-Do List: DAQ • Existing components: • sub-nanosecond FPGA-base ADCs are commercially available • 16-anod fast PMTs (e.g. H6568 – 200nm, 150ps). • We will work with other LC collaborators on DAQ chain. O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  20. Summary & To-Do List: Optical Surfaces • surface quality control: roughness less then 30nm • reflectivity measurement at grazing angles in UV • polishing techniques give surface finish comparable to high quality commercial mirrors. • reflectivity measurement of the reference mirror. • Coat polished samples with Al, Al+MgF2 and perform reflectivity measurements O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

  21. To-Do List: Simulation • G4OpBoundary class is being now fixed by Geant4 team to work with complex geometries. • thus it should be possible to properly implement “honey-comb” geometry (its construction now has become feasible due to improved shim polishing techniques) • find optimal absorber, shape and size of conduits, gas/absorber ratio. Stay tuned! O. Atramentov, American Linear Collider Workshop, Cornell U. 13-16 July 2003

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