CUORE Detector Calibration System

CUORE Detector Calibration System Karsten M. Heeger University of Wisconsin Detector Calibration System Leader US CUORE Annual Review LBNL, August 2-3, 2011 1

Outline Calibration system requirements Scope and system elements Progress at Wisconsin since 2010 improved DCS failsafe system and positioning integration work system testing hardware for 4K test readiness and optimization for DCS fabrication cleaning, assembly, and installation planning Schedule and personnel DCS milestones and CD-4 requirements 2

Calibration of CUORE Bolometers Detector Calibration System Provide absolute energy calibration of energy spectrum in each bolometer I. Gain Stabilization For each bolometer an energy pulse generated by a Si resistor is used to correct pulse amplitudes for gain instabilities ( every 5 min). Summed spectrum from all detectors [counts/(kev kg yr)] 5000 4000 3000 2000 II. Calibration of individual bolometer III. Voltage-Energy Conversion Fit of a calibration measurement with a gamma source (e.g. 232 Th) of known energy. Energy calibration performed regularly. (~ monthly). 511keV calibrate with γ-sources need 5+ lines visible in calibration spectrum energy accuracy goal: < 0.05 kev 583keV 208 Tl 1000 Karsten Heeger, Univ. of Wisconsin 0 LBNL, August 2-3, 2011 3 500 1000 1500 2000 2500 3000 911keV 228 Ac Sum calibration spectrum of Cuoricino with 232 Th source 969keV 228 Ac 2103keV 1592keV single escape double escape ββ0ν 2615keV 208 Tl

CUORE Detector Calibration System Key Issues Thermal loads meet heat load requirements of cryostat Calibration rate of < 150mHz for each bolometer to avoid pile-up Sources can be replaced. Other source isotopes can be used if necessary need to (e.g. place 56 Co sources has next been to studied) Shortest possible crystals calibration to allow calibration time (< 1 week), of minimize all bolometers loss in detector livetime. Negligible contribution to radioactive background in the ββ0ν region Minimize the uncertainty in the energy calibration (< 0.05 kev) Calibration uncertainty - affects the resolution of the detectors - is one of the systematic errors in the determination of the 0νββ half life 4

Calibration Source Simulations radioactive sources: 56 Co and/or 232 Th 56 Co: proton activated Fe wire; 232 Th: Thoriated Tungsten wire ~100 events over background per peak are required for successful calibration both have been used in Cuoricino 5

Calibration Source Simulations source positions Optimization of Source Strength, Position, and Distribution 0 60 external sources EXT SOURCES (symmetric) INT SOURCES internal sources achieve uniform illumination of all crystals with internal/external sources determine max source activity, minimize calibration time MC HEX STILL 6

Calibration Source Simulations source positions 0 60 external sources EXT SOURCES (symmetric) INT SOURCES internal sources Optimization of Source Strength, Position, and Distribution achieve uniform illumination of all crystals with internal/external sources determine max source activity, minimize calibration time event rate in crystals (2615 kev) MC Max hit rate of 150 mhz per crystal to avoid pile-up, based on Cuoricino experience Activity per discrete source: internal/external sources: 130 mbq/633 mbq internal/external sources (top/bottom) : 131 mbq/ 728 mbq (higher activity to compensate for z- variation) HEX STILL layer 6 6

Detector Calibration System insertion of 12 γ sources that move under own weight motion system insertion and extraction of sources in and out of cryostat guide tubes no straight vertical access source strings move under own weight in guide tubes source locations vertical cross section of the cryostat 300K 40K 4K 0.7K 80mK 10mK Pb shield detectors @ ~10mK Pb shield top view of detector array with source positions 7

Detector Calibration System insertion of 12 γ sources that move under own weight motion system insertion and extraction of sources in and out of cryostat guide tubes no straight vertical access 300K source strings move under own weight in guide tubes 40K source locations 4K 0.7K 70mK guide tubes 10mK Lead shield detector support plate bolometers @ ~10 mk top view of detector array with source positions 8

Cryogenic Considerations Calibration system must be integrated with complex detector cryostat Must meet available cooling power requirements at all thermal stages Stage T [K] Cooling power available to calibration [W] Static heat load from guide tubes Radiation from source string at 4K 40K 40 50 ~ 1 ~1 -- 4K 4 5 0.3 0.02 -- 0.7K 0.6 0.9 0.55m 0.13m 0.08µ 70mK 0.05 0.1 1.1µ negligible 0.3µ 10mK 0.01 1.2µ 1.07µ 0.08µ detector 0.01 < 1µ -- 0.25µ Thermal conductivity of guide tubes Radiation heat inflow from 300 K Heat radiated by the source strings Thermal conductivity of the source strings Frictional heat during source string motion Guide Tubes and Thermal Coupling internal Stainless Steel Copper Perfect thermal coupling Weak thermal coupling external 300K 40K 4K 0.7K 70mK 10mK Lead shield Detector region 9

Calibration Motion System Motion Box Drive Spool vacuum flange string guide emergency switch electrical feedthrough motor, gears, and encoder drive spools can be removed with clean bag for individual source exchange source string spool load cell home limit switch vacuum feedthrough with shaft 10

Calibration Source & Guide Tubes Source String Kevlar string flexible, moves under gravity in guide tube small mass: < 5 grams vertical distribution of source activity can be adjusted 30 capsules crimped and evenly spaced over 85 cm of Kevlar string source wire Cu crimp PTFE heat shrink ~10mm Guide Tubes stainless and/or machined from solid, low-background copper can use teflon tubes for bends radioactive source wire 232 Th: Thoriated Tungsten wire 56 Co: proton activated Fe wire 11

Calibration Thermalization to 4K 300K Sources must be cooled to < 4K to meet heat load requirements Strong mechanical contact is needed between the source carrier and a heat sink at 4K Thermalization at 4K Flange Magneto-mechanical 4K thermalization mechanism 40K 4K Lead shield 0.7K 70mK 10mK solenoid linear actuator Lead shield source string pushing blade Detector region CUORE cryostat 12

Failsafe and Positioning Systems Improved Failsafe Positioning Encoder measures spooling of source string. Load cell measures tension in string. Allows rough position determination in cryostat. Monitors insertion and retraction. Software limits for automatic shut-off. Emergency switch protects mechanically against excess tension. Home limit switch provides mechanical zero position of source home position. Induction-based proximity sensors detects position of source capsules and counts them. Gate valve closes motion box during regular data taking Failsafe during power and pressure failure, with mechanical and software switch. 13

Integration Effort at Wisconsin DCS Integration Effort at Wisconsin and with CUORE Integration Team CUORE cryostat is complex In early 2011 UWisc integrated DCS model into up-to-date cryostat model. 4 interferences above 300K: - 3 solved by rotating/customizing DCS parts - 1 solved by changing pulse tube part cryostat model incomplete below 4K: - top support, bottom support plates missing - outdated detector frames Frascati integration team working on many critical CUORE issues, cryostat is one of them 14

Outstanding Integration Issues Top Support Plate+DCS+Wiring Reveals Interferences Further integration work needed in detector region - Italian integration team proposes to change guide tube routing: original routing, proposed new routing - Monte Carlo studies of backgrounds in progress - decision by end of August 2011? Connection to bottom plate to be finalized 15

Phased System Testing Program Calibration System Testing Motion/mechanical tests at 300K extensive tests performed to date, verified and characterized motion and instrumentation complete but ongoing Motion/mechanical tests at 77K tests mechanical operation of thermalization mechanism and cryostat parts for > 5 year lifetime complete but ongoing Motion/thermal tests at 4K (in CUORE cryostat at LNGS) hardware built for test of 1 motion box and typical guide tube routing, integrated test of thermalization, depends on CUORE cryostat schedule in preparation, planned for early 2012 Motion/thermal tests at 4K (standalone) - setting up independent 4K test chamber in Wisconsin (He bath and pulse tube) - tests in fall 2011 will allow UWisc to make measurements with thermalizaton mechanism and learn and prepare for 4K testing at LNGS 16

Calibration System Testing & Schedule Figure: Peterson 17

Calibration System Testing & Schedule start of cryostat assembly = start of UWisc presence at LNGS Figure: Peterson 17

Calibration System Testing & Schedule start of cryostat assembly = start of UWisc presence at LNGS cryostat assembly procedure under development, expect 4K test in early 2012 Figure: Peterson 17

System Testing at Wisconsin Mechanical motion test stand at 300K Outgassing measurements and baking System tests at 77K Setting up independent 4K pulse tube 18

Load Cell Data Mechanical motion test stand at 300K load cell data shows unique geometry of guide tube system load cell guide tubes webcam proximity sensor load cell data profile limits up source moves reliably under its own weight position accuracy ~ 1-2 mm reproducible load cell pattern allows safe operation down 19

Improved Positioning with Limit Switch emergency kill switch home reset switch - Home position from encoder drifts over time by about ~2mm - home switch resets home position to increase positioning precision - engages at low force ~0.3N Position (cm) drift of home position over time without home reset switch Time (hrs) 20

Mechanical Testing at 77K Thermalization Mechanism Prototype Testing source string & capsule CUORE requirements - expect calibration ~ 1/month - 60 cycles per string over 5 years - 180 cycles per mechanism over 5 years - expect < 500 cycles including commissioning thermalization blade Testing > 27000 cycles for 1 s push and 1 s release at 300K > 15000 cycles for 1 s push and 1 s release at 77K > 400 cycles for 30 s push and 30 s release at 77K > 9000 cycles for 1 s push and 1 release on top edge of blade at 77K > 800 cycles for 1 s push and 1 s release on undersized capsule at 77K no jamming, no wear of mechanism, no significant wear on capsules 21

Calibration System Test at 4K Integrated test of one motion box and inner and outer guide tubes at 4K in CUORE cryostat at LNGS test of the key DCS components in empty CUORE cryostat thermalization mechanism motion box above 300K thermal Cu shunt to improve thermalization - requires CUORE cryostat at LNGS, DCS schedule follows on-site work - uses old guide tube routing around lead shield - hardware designed and built for 4K test does not reflect proposed change of guide tube routing through lead shield. 22

Hardware for 4K LNGS Test see demonstration hardware at review 23

Readiness for DCS Production Building and optimizing jigs for guide tube production developed procedure for precision bending of copper guide tubes - meet bending radius to < 1mm - determine radius with digital image and Autocad radius fitting - max elliptical deviation of inner radius ~0.006 (0.15mm) Gundrilling method for guide tube fabrication customized jig for bending, welding, and leak checking 300K-4K stainless guide tubes - built 300mm length for 4K test, can increase to 500-800mm length if needed. would eliminate segmentation of guide tube in detector region - fabrication tools easily reconfigurable for new routing in cryostat 24

Cleaning and Assembly at Wisconsin - New class-1000 cleanroom at Wisconsin with cleaning capabilities. Meets UHV requirements. - Will be used for source fabrication and final cleaning of motion box parts and for cleaning of DCS cryostat components. - Will be used for final acceptance testing just before shipment. 25

Installation Planning at Wisconsin 1:1 wooden model of cryostat flanges 4K 40K 300K 1:0.75 model printout of cryostat 26

Installation Planning at Wisconsin 1:1 wooden model of cryostat flanges 300K-4K guide tubes in jig 1:0.75 model printout of cryostat - visualize and develop installation procedure before installation at LNGS - practice installation of guide tubes and indium seal 27

Calibration Team Current Scientists K. Heeger (faculty) Daniel Lenz (postdoctoral fellow, UWisc) L. Ejzak (graduate student, 5th year) A. Dally (graduate student, 2th year on CUORE) S. Sangiorgio (postdoctoral fellow, now at LLNL) Engineer/Designer (UWisc) Ken Kriesel (mechanical engineer) Glen Gregerson (designer Planned in FY2012-13 Scientists K. Heeger (faculty) Daniel Lenz (postdoctoral fellow, at UWisc) A. Dally (graduate student, 2th year on CUORE) Researcher T. Wise (senior researcher) Engineering as needed Communication (Wisconsin and CUORE cryostat group) weekly meetings with Wisconsin engineer phone meetings with cryostat group in Milan integration meetings at time of collaboration meetings on-site for DCS testing on-site long-term for cryostat assembly and DCS testing on-site installation and testing 28

Calibration System Milestones completed achievable if DCS 4K test at LNGS by Spring 2012 need to commit to building remaining DCS hardware in summer 2012 29

Revised CD-4 Requirements Proposed Change to Calibration System CD4 Deliverables Objectives for Revised CD-4 Criteria: 1. ensure DCS functionality to greatest extent possible 2. make deliverable independent of cryostat and on-site work as much as possible based on vacuum requirement from cryostat all requirements have essentially been met with 4K test hardware 30

Summary Wisconsin has completed design, mechanical tests, and vacuum testing of motion box. Developed source fabrication procedure. Continue long-term motion testing. Built hardware for 4K calibration test in cryostat at LNGS. Optimizing fabrication procedures for remaining DCS hardware. Addressing outstanding integration challenges together with CUORE integration team in Italy. Will finalize DCS integration in detector region in Fall 2011. Develop independent capabilities at Wisconsin for cleaning, assembly, and mechanical and thermal testing of DCS components to greatest extent possible. Developing installation plans and procedures utilizing 1:1 model of cryostat at Wisconsin. 31

` Karsten Heeger, Univ. of Wisconsin LNGS, March 28-29, 2011 32