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VELO Decisions Thomas Ruf LHCb week February 2001 Interference with LHC machine   LEMIC, January 2001: Presentation of the VELO Vacuum Chamber design

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VELO Decisions Thomas Ruf LHCb week February 2001 VELO Decisions  Sensor choice  Position of Off-Detector Electronics

Text of VELO Decisions Thomas Ruf LHCb week February 2001 Interference with LHC machine   LEMIC,...

VELO Decisions Thomas Ruf LHCb week February 2001 Interference with LHC machine LEMIC, January 2001: Presentation of the VELO Vacuum Chamber design was well received, see also conclusion from A.Rossi. The subsequent discussion in the LHC technical board was also quite positive (unofficial). BUT, BUT, possible request from the LHC machine: Downtime of LHC in case of a worst case accident should be limited to 2 weeks. This means for LHCb: Replace VELO Vacuum Chamber with spare beam pipe RICH1, inner tracker ? continue LHC running without LHCb Detailed planning needs to be worked out how this could happen. Started by M.Ferro-Luzzi in context of risk analysis. Need a spare beam pipe. Fast switch to spare beam pipe needs to be taken into account in design for Station1 and Rich1. VELO Decisions Thomas Ruf LHCb week February 2001 Conclusions Conclusions presented by A.Rossi (LHC-VAC) The LHC/VAC group accepts: Foil not withstanding atmospheric pressure - compromise between safety and physics performances. 2 phases CO2 cooling system in secondary vacuum. Provided that: Risk assessment complies with LHC standards. Design developments in close collaboration/supervision with CERN. Prototype and testing prove principles. Replacement of the vacuum chamber in the case of a major accident. Yearly design reviews, 2 day workshops: lApril 2001 lFebruary 2002 lFebruary 2003 VELO Decisions Thomas Ruf LHCb week February 2001 VELO Decisions Sensor choice Position of Off-Detector Electronics VELO Decisions Thomas Ruf LHCb week February 2001 The VELO Sensor Choice Unanimous decision at the 3rd VELO workshop, 26 January, to adopt n-strip detectors as the baseline for the TDR. Driving arguments for a technology choice are: Resolution Signal / Noise Radiation hardness Availability Problem: Cannot get all the good things at the same time. Find a solution of which we are convinced it will work. Improvements are still possible at a later time. Problem: Cannot get all the good things at the same time. Find a solution of which we are convinced it will work. Improvements are still possible at a later time. p-strip OR n-strip detectors ? TP: 150 m thin n-strip detectors with 40 m minimal strip pitch since then: trying to prove feasibility and to improve VELO Decisions Thomas Ruf LHCb week February 2001 What do we have tested? n-on-n detectors from HAMAMATSU Thickness: 300 m, Smallest strip pitch: 40 m p-on-n detectors from MICRON: Thickness: 200 m ( 150 m and 300 m exist but not tested Smallest strip pitch: 32.5 m for the r-detector and 24.4 m for the phi-detector p-on-n detectors, DELPHI module, double sided readout: Thickness: 310 m, Smallest strip pitch: 42 m n-side 25 m p-side ( only every second strip read out But LHCb is special: Small strip pitch ! + measurements from ATLAS, CMS, ROSE, But LHCb is special: Small strip pitch ! VELO Decisions Thomas Ruf LHCb week February 2001 Effect of Radiation from Rose collaboration based on diodes NOT directly comparable to strip detectors VELO: ~ 1 x n eq cm -2 / year at r=8mm Increase of depletion voltage after irradiation. Lifetime of the VELO is limited by the maximum voltage which the detectors can stand. Because of small strip length and low temperature, the VELO is not limited by the increasing current. Detector will slowly die from inside to outside: The region at r>11mm will last twice as long as the region at r=8mm. depletion voltage ~ d 2 use thinner detectors BUT signal ~ d or run detector not depleted n-type p-type radiation VELO Decisions Thomas Ruf LHCb week February 2001 What is the difference of a n-strip and p-strip detector after irradiation ? Charge collection efficiency and resolution of an irradiated double sided silicon microstrip detector operated at cryogenic temperatures. Nucl.Instrum.Meth.A440:17-37,2000 Measurements done using a double sided detector If the detector is not fully depleted, charge is spread over a large area on the p-side. Effect only seen for small strip pitches (

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