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Cooling detectors in particle physics Gavin Leithall CCLRC Rutherford Appleton Laboratory

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Gavin Leithall, RALPlacement Conference CCLRC Rutherford Appleton Laboratory Government funded central research laboratory which supports a wide range of university research activities Located in Oxfordshire I work in the Particle Physics Department on the vertex detector for the International Linear Collider

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Gavin Leithall, RALPlacement Conference The International Linear Collider Will collide beams of electrons and positrons with energies from GeV (upgrade to 1000 GeV) Scheduled to begin operation in 2015 Will have a total length of about 30 km Intended to complement the Large Hadron Collider by being a more precise measuring tool Together they are hoped to discover new particles and test theories (e.g. the Higgs Boson and Supersymmetry)

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Gavin Leithall, RALPlacement Conference What is a vertex detector? Collisions produce a spray of high energy particles A large detector is built around the beam pipe to work out what happened in the collision The vertex detector is the one closest to the collision point Used to reconstruct particle tracks to determine their production point (vertex) Required to have little material to minimise scattering

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Gavin Leithall, RALPlacement Conference Linear Collider Flavour Identification LCFI (my project group) is designing the vertex detector for the ILC The detecting elements called ladders are layered in concentric barrels The hits generated when a particle passes through enable track reconstruction

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Gavin Leithall, RALPlacement Conference Detector Technology The main technology being developed by LCFI is the Column Parallel Charge Coupled Device (CPCCD) These are composed of tiny pixels which accumulate charge when particles pass through Similar to the CCDs in digital cameras, but with a much faster readout The readout chips are placed at the end of the ladders Classic CCD Readout time N M/F out N M N Column Parallel CCD Readout time = N/F out

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Gavin Leithall, RALPlacement Conference Detector Cooling The vertex detector will produce heat which will need to be removed. It will also need to be maintained at a constant operating temperature (possibly as low as -70 deg C) It therefore needs a cooling system to meet these requirements Conventional cooling systems would add material to the detector volume, so are not ideal Blowing cold gas from the ends of the detector is a possible solution My project is to investigate the effectiveness of this

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Gavin Leithall, RALPlacement Conference Cooling Test Rig Built a system to produce a controlled nitrogen gas flow with –Variable temperatures (-100 o C to 20 o C) –Variable flow rates (0-20 litres / min) Built a system to read temperatures from platinum resistors Designed programs to enable remote control of both of these systems Gas Mass flow controller Heat exchangerFilter Regulator Heater Thermocouple Liquid nitrogen Control Box To Computer

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Gavin Leithall, RALPlacement Conference Detector model A quarter barrel model was decided upon because it would be easier to build than a full barrel, while maintaining all the essential physics. It has: –Stainless steel ladders and aluminium end-plates –Resistors in the place of the readout chips to simulate heating –Platinum resistors at various positions within the quarter barrel

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Gavin Leithall, RALPlacement Conference Quarter barrel construction End plate InletOutlet Side view of quarter barrel Resistors Ladders End plates Gas In Gas Out

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Gavin Leithall, RALPlacement Conference The Physics Quarter barrel Temperature = T q Gas In Temperature = T i Flow rate = v Gas Out Temperature = T o Flow rate = v Heating power = P i Power lost to surroundings = P s Surrounding temperature = T s

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Gavin Leithall, RALPlacement Conference Formulation of the problem P g (power gain of gas) can be calculated by P g = cv (T o – T i ) (c = specific heat capacity) Using energy conservation P i = P s + P g Using Newtons Law of Cooling P s = L (T q – T s ) (L = thermal loss coefficient) A graph of (P i - P g ) against T q should –Be a straight line with gradient L –Pass through P i – P g = 0 when T q = T s

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Gavin Leithall, RALPlacement Conference This graph –Is a straight line with a gradient giving L ~ 0.26 W / deg C –Suggests a room temperature of T s ~ 19 deg C

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Gavin Leithall, RALPlacement Conference A hypothesis I can make a hypothesis about the form of P g : P g = hv (T q – T i ) –h is the heat transfer coefficient, assumed constant, but could be a function of v, T q, T i This can be tested by plotting graphs of P g against the other variables

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Gavin Leithall, RALPlacement Conference This graph gives strong support to the hypothesis that P g is proportional to (T q – T i ) By plotting the gradient (i.e. P g / (T q – T i )) of each line against its flow rate, the hypothesis can be tested further

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Gavin Leithall, RALPlacement Conference This graph supports the hypothesis that P g / (T q – T i ) is proportional to v The gradient of this graph gives h ~ W / deg C / (litre/min)

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Gavin Leithall, RALPlacement Conference Conclusions Thermal loss coefficient L ~ 0.26 W / deg C The form of P g is P g = hv (T q – T i ) Heat transfer coefficient h ~ W / deg C / (litre / min) Maximum P g ~ 5 W when v = 20 litres / min and (T o – T i ) ~ 11 deg C

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Gavin Leithall, RALPlacement Conference Summary Testing the effectiveness of gaseous cooling for the vertex detector for the International Linear Collider Results so far show behaviour that is consistent with predictions Move on to investigate new configurations –More inlets, and with different positions –Different sizes and angles of inlets

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Gavin Leithall, RALPlacement Conference

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Gavin Leithall, RALPlacement Conference

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Gavin Leithall, RALPlacement Conference Plotting the value of P g predicted by the hypothesis against the value obtained by the earlier measurement provides a useful crosscheck This yields a graph which provides good support for the hypothesis

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