Pixel 2002 International Workshop On Semiconductor Pixel Detectors
Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays New Directions in Mechanics and Cooling for Pixel Detectors W. O. Miller Innovative Technologies International (iTi) iTi Wei Shih Allcomp Corporation [email protected] iTi: ATLAS # 1 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Objectives ATLAS is fielding a large Pixel Detector which represents a significant advancement over existing silicon-based detector systems Achievements have been significant, the design is well established and supported with extensive testing- With some knowledge of the past, my objective was to step back and to
look at the design, focusing on mechanical issues from a different perspective Hopefully, the outcome will influence future detectors To accomplish this objective, we first briefly review mechanical and cooling concepts embodied in the ATLAS Pixel Detector Large in size, composed of both barrel and disk detector elements Design was faced with major cooling issues; highly distributed heat loads, totaling over 15kWatts Tight constraints on radiation length and stability Some of the service issues are still emerging We conclude by summarizing an approach being studied that is a significant departure from the approach taken by ATLAS [email protected] iTi: ATLAS # 2 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays ATLAS Pixel Detector Pixel Detector 1744 modules 3 barrel layers 3 disks, each end Heat loads ~7W/module 13kW in detector space 17.1kW in pixel volume 38.6kW total, balance from cables General Design Goals Stability, ~10 microns Radiation length-normal incidence Cooling
Evaporative (C3F8), two-phase flow -20C inlet, providing -6 C at detector For 17kW, mass flow rate of 185g/s [email protected] Local supports <0.7% Frame <0.4% Low mass High Reliability 10 year life cycle Low maintenance iTi: ATLAS # 3 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Coolant lines 1.2g/s Local Supports Disk local support Composite Ring C-C sectors Barrel local support Shell Stave Coolant lines Modularity of detector Side A, 35 flow circuits Side C, 45 flow circuits
shell stave Layer 1 and Layer 2 2.6g/s B-Layer 3.6g/s [email protected] iTi: ATLAS # 4 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Barrel Assembly Mechanical design approach is mature, testing of key components complete stave coolant connections Details of services, connections and routing are in being finalized bi-staves vapor return lines [email protected] Courtesy of Thomas Pfaff (IVW) iTi: ATLAS # 5 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays
Barrel Structure CF-PEEK elements with pillars, bonded between outer shell and inner skins ==> Sandwich structure to allow screwing of SSR to halfshell Screws Courtesy of Thomas Pfaff (IVW) CFRP faceplates CF-PEEK core elements [email protected] iTi: ATLAS # 6 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays View of End Section (cooling) Side C: 45 outlets and 45 inlets End section frame (frame joint) Return from barrels Vapor returns Barrel capillaries Service panels (truncated in length) Capillaries for both disk and staves [email protected] iTi: ATLAS # 7
Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Plumbers Nightmare Illustration represents the beginnings of the packaging required as the services pass out of the Pixel Detector Support tube 1/3rd of a quadrant bundled together Courtesy Fred Goozen LBNL [email protected] iTi: ATLAS # 8 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Radiation Length Issue Mass-kg Courtesy of D. Costanzo-LBNL 33.1
35 30 25 20 15 10 5 0 2.6 4.3 Modules Frame Other Total mass breakdown Includes barrel pixel support tube [email protected] Radiation Length-% 8 6.78 Normal Incidence 6 4 2 0.52 0.34 Modules Hybrid
1.04 0.24 0.36 Shells Frame 0 Staves 3-Layers iTi: ATLAS # 9 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Cooling System Concept based on controlled boiling in a stave or sector Saturation pressure in stave or sector nominally 1.7bar entrance, 1.3bar exit Capillary feed to stave or sector, with inlet to capillary of 9.3bar As tested, each flow circuit, i.e., bi-stave and adjacent sector pair, use upstream and down stream pressure regulator to control temperature Extrapolation for 80 circuits: 160 pressure regulators (80 inlet and 80 outlet), and 80 outlet temperature regulators Plumbing, 3 connections in each barrel cooling line and 2 each for the disk
from the local support to the end of the frame (PP0) Side C: 33*3*2+12*2*2=246 mechanical connections Side A: 23*3*2+12*2*2=186 additional mechanical connections Roughly, 432 mechanical fittings to make and check at each assembly and disassembly The evaporative cooling system is quite sophisticated, but at what expense to earlier goals of low-mass, low radiation length, and possibly at some impact on reliability. [email protected] iTi: ATLAS # 10 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays New Design Option Passively remove heat from modules, without using forced convection Transfer the heat from the modules to collection points, where the energy is removed by convection Circulated fluid could be either single or two phase, but presently assumed to be two phase Use passive heat removal system to extract heat from cables as well Reduce fluid connections, potentially by a factor of 10, or so Reduction constrained only by desire for redundant flow circuits Efficient passive heat removal can not be provided solely by highly conductive composite Proposal uses evaporative fluids [email protected] iTi: ATLAS # 11 Pixel 2002
International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays We propose that detectors involving hundreds of cooling lines can be simplified using heat pipes Propose to explore this option using the ATLAS barrel system as an example Heat pipes transport heat efficiently from the evaporator to the condenser Heat Pipes (HP) Very efficient, effective thermal conductivity about 1000x of Cu Heat out Heat in Here, the two sections are close coupled Design options 1st, HP that replaces stave, eliminating OMEGA piece, Al tube, and grease film. 2nd, HP becomes part of the structure, eliminating the outer shell Options are introduced to lower radiation length
[email protected] or c p a V ore con sati n e d n atio r o p eva Annular wick iTi: ATLAS # 12 on Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Typical Wick Geometries Heat Pipes for HEP Application Must achieve low radiation length Must be lightweight
Conceivably can be used as part of the structure, with modules mounted directly Proposal Thin Carbon-Carbon (C-C) shell with integrated wick C-C wall porosity sealed by the wick material Arteries can be added, but another degree of complexity [email protected] Process is to find the best tube size and wick configuration that minimizes mass and thickness, as a function of candidate fluids Screen wick Axial groove wick simple More complicated Slab wicks with circumferential grooves iTi: ATLAS # 13 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays C-C What is it? Carbon-Carbon Denotes composite composed of carbon (or graphite) fibers in a carbon matrix C-C may be formed as flat laminates or into structural shapes Material properties can be enhanced by densification of the carbonized
material, followed by heat treatment to obtain high modulus, high strength and high thermal conductivity Carbon infiltration by CVD , and or pitch C-C Material: properties are tailorable 2D K1100 Laminate, E~3X AL, K~2X AL, CTE ~-0.75ppm/K Kz= 45 W/mK, ~50-60X resin based laminate C-C characteristics Typical radiation length of 23cm Hydrophobic, insensitive to moisture Negative CTE, ranging from 0.5 to 1.5 ppm/K depending upon laminate layup, expands when cooled Strength rivals steel, but strain to failure is lower C-C sandwich panel [email protected] iTi: ATLAS # 14 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays HP Fluid Options Basis for selection Low temperature two-phase fluids Preferably low saturation pressure in temperature range of interest, -20 to
10C Fluid surface tension and heat of vaporization criteria Very important as we will see next Process has just started Selection of fluid Design of HP Integration with structure [email protected] iTi: ATLAS # 15 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Candidate Fluids-Groove Wick Description Fluid Conditions NH3 CH3OH C4H10 R12 C3F8 C4F10 Saturation Pressure-bar Temperature-C Groove Wick Dimensions 2.9
FOM-kW/cm2 16140 1735 1375 1079 745 510 Ammonia: NH3 Methanol: CH3OH Perfluoropropane: C3F8 [email protected] Isobutane: C4H10 Perfluorobutane: C4F10 R12: CCL2F2 FOM l l iTi: ATLAS # 16 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays 1st Order Groove Wick
Ammonia fluid satisfies the goal of a small diameter HP rather easily Advance notice of this comes from the fluid Figure of Merit (FOM) calculation FOM brings together key fluid parameters that are important to HP applications. Methanol does not attain the goal of 55W with a simple wick geometry as hoped Option to a groove wick with constant dimensions is to change shape with axial dimension, improving the wick permeability Changes to groove geometry are being investigated Other candidate fluids show major short comings with the simple groove wick Possible one of these fluids will work with another wick geometry, e.g., screen wicks Work will continue to select a fluid and wick geometry to minimize the HP profile dimensions [email protected] iTi: ATLAS # 17 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Description HP stave with step-up/stepdown geometry for axial overlap
HP is a stiff tube, overcoming gravity sag between supports Modules are mounted on flat machined C-C plates Introduce condenser manifold 1st Structural Option Module thermal management piece HP Condenser manifold Improvements Eliminates several ATLAS stave components Condenser manifold eliminates the 432 tube connections in the tracking volume Condenser manifold can be built with multiple coolant passes to add redundancy [email protected] iTi: ATLAS # 18 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Condenser Manifold Condenser manifold objectives Condenser manifold is an external flow circuit, replacing the 80 or so flow circuits Condenser is supplied with multiple flow circuits, say 3 for system redundancy
Manifold accepts heat from ends of the heat pipes We choose to confine the heat transfer to nominally 40mm axial distance at end of HP If necessary, we will use surface area enhancements, like foam to reduce temperature drop in the manifold Fluid in manifold could be C3F8, using the system as developed by ATLAS [email protected] iTi: ATLAS # 19 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays HP-Structure Integration Adjacent HP tubes are joined with thin composite strips, upper and lower strips The strips form a circumferential step-up/stepdown pattern, providing a continuous shell like structure Structural concept is similar to the CMS barrel concept Module Overlapping Provided circumferentially by step pattern Step-up/step-down pattern is molded in the axial strip to permit overlapping in the axial
direction [email protected] 2nd Structural Option cable support down/up, 2 directions C-C tube structure with C-C facings iTi: ATLAS # 20 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Stave Support Options Gravity sag solutions Case (a)- HP tubes tied together with rings Case (b)-HP tubes stave only Case (c)- HP tubes integral with shell Results Case (a) sags excessively Case (b), stave with 6 supports will sag 28m, a supporting shell <3 m Case (c), composite strips between HP tubes sag <8m with module and cable weights added
case a case b case c Radiation length Preliminary results for lowest mass and radiation length favor case (c) [email protected] iTi: ATLAS # 21 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Benefits/Risks Potential Benefits of Passive Heat Extraction with Heat Pipes in the ATLAS Pixel System Improved local thermal stability-passive, not subject to change by individual performance of regulators Major reduction in number of tube connections, and associated mass Elimination of 160 pressure regulators Improved structural thermal stability, eliminate adjacent coupling of Al tubing Less mass, lower radiation length at >1 Potential for modularity of 1 versus present modularity of 2 Improved system reliability and functionality Risks Demonstrate C-C heat pipe technology with 10 year life Address low mass and sealability Address thermal design, leading to pipes of the order of 6mm diameter
Demonstrate stability of HP fluid in radiation environment [email protected] iTi: ATLAS # 22 Pixel 2002 International Workshop On Semiconductor Pixel Detectors for Particles and X-Rays Conclusion HP Design Construction concepts for achieving sealed C-C are being formulated 1st order specimens of wall structure have been constructed Performance studies for wick geometries are underway HP Testing Expect to test a1/2 length 55W HP composed of carbon-carbon elements by end of CY2002 Financial support Provided by DOE Phase I SBIR Related application NASA Nuclear Electric Propulsion initiative in sore need of carbon-carbon HP radiator, using C-C sandwich facings [email protected] iTi: ATLAS # 23
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