Scope Review (draft): Purity Monitors for DUNE Jianming Bian (UC Irvine) 1
Scope and Motivation • Build 6 PrMs in the DUNE cryostat, 4 standard and 2 long • Build 2 standard PrMs within recirculation (inline), reduced from 4 after studying diagram of recirculation system • Detector and cryogenic operation: monitor argon filling during commissioning, alert pump and cryogenic accidents during operation, alert unexpected contamination • Provide benchmarks LAr purities for recirculation studies and TPC calibration • Measure e-lifetime for data analysis • Measure purity stratification • Verify CFD 2
Purity measurements • Gas Analyzers: measure GAr purity, useful to alarm cryogenics issues • Purity Monitors: localized high precision LAr purity measurements, alarm cryogenic (inline PrMs) and cryostat (cryostat PrMs) issues, also useful in recirculation studies and analyses • TPC: use cosmic rays to measure electron lifetime in cryostat, useful for analysis. If there are enough cosmic rays could measure electron lifetime across the detector. DUNE FD doesn’t have enough cosmic rays for this. 3
Cryostat Purity Monitors Two strings of purity monitor assemblies on TCO and back sides, each string mounts 3 purity monitors on a supporting tube, in total 6 purity monitors in cryostat Need ports for straight deployment One of DN250 instrumentation ports on each side, if not available then use part of manhole on each side Similar system runs successfully in ProtoDUNE-SP Locations for Inline Purity monitors under discussion 4
Flange for straight deployment • Guarantee electronic and optical connectivity 3 X Optical feedthroughs • Completed PrM assembly needs to be tested in vacuum tube before insertion • Quartz fibers need to be protected and Side view can not be bent too much 2X 1/5” VCR (For gas fill and relief) 1X 1.33” CF Flange 4X 2-3/4 CF Flanges (Vacuum pumping) (3-HV and signal) Custom support tube (1-Fiber optics) adapter, protect optical fibers HV feedthroughs
Inline Purity monitors 2 PrMs outside of cryostat inline with cryogenics system, before and after filtration system PrM PrM 6
ProtoDUNE-SP Purity Monitors Q anode /Q cathode = e -tdrift/ t Top PrM M. Adamowski et al., JINST 9, P07005 (2014). Middle PrM Individual PrMon: • A miniature TPC Bottom PrM • Xe flash lamp light source Dirty LAr pump • Al-Ti-Au photocathode for drift electron generation • Faraday cage and optimized grounding scheme for minimal noise pickup • Cathode/anode readout electronics Clean LAr Distribution At ProtoDUNE-SP, all 3 purity monitors have same drift length, 25 cm Cathod/Anode disks, field shaping rings and grids from ICARUS PrMs 7
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Improved PrM Signal in ProtoDUNE-SP • PrM HV varied (0.25 kV-3 kV) allows for range of drift time from 150 us to 3 ms ProtoDUNE PrM signals at e-lifetime = 6 ms • Increase UV light by using 8 optic fibers for each PrM • At ProtoDUNE-SP regular purity 6 ms, Qa/Qc = 0.7 à no saturation • Each PrM measurement lasts 20 seconds with 200 UV flashes, provide high precision, localized electron lifetime • Measured e-lifetime at ProtoDUNE-SP: 35us - 8 ms 9
Charge Questions • How was output from the purity monitors used in ProtoDUNE and for which operational phases was the data collected critical? • Is the purity stratification observed within the ProtoDUNE-SP cryostat real and if so, is this consistent with initial purity measurements from cosmic rays? • What are the limitations of the purity monitors in terms of measuring high purity levels and what are the benefits that would be obtained by implementing proposed improvements to these devices? • Are the proposed number of purity monitors per far detector module (10 total, 6 inside cryostat, 4 inline within cryogenic infrastructure) necessary to meet critical system requirements? • Do the purity monitors need to be designed to operate over the full lifetime of the experiment? • Are the proposed mechanisms for supporting the monitors within the cryostat and connecting them to the outside of cryostat mechanically sound and cost effective? 10
1. How was output from the purity monitors used in ProtoDUNE and for which operational phases was the data collected critical? • July 23 - Sep 29: Continuously (hourly) monitor LAr purity during filling. Data taking started when bottom PrM fully submerged in LAr. Found saturation of LAr filter during filling —> report sent to cryogenics team and filter cartridges regenerated • Sep - Dec 2018: Monitor LAr purity a few times per day during beam data taking period. This alerted the experiment to several problems: recirculation pump stoppages, false alarms, problems from the cryostat level gauges. This prevented situations which otherwise would have gone unnoticed for some time, with severe consequences to the ability to take data. Neither the gas analyzers nor the TPC caught these problems in time. • Sep 2018 - Present: Monitor LAr purity during cosmic ray data taking. Provides a benchmark for LAr purities for recirculation studies and TPC calibration by measuring the e-lifetime for the TPC. • Critical to LAr filling, commissioning and data taking 11
Monitor LAr Purity during filling Monitor purity during LAr filling, find saturation during the filling As soon as the lowest purity monitor was immersed: ~40 us -> 7.5 ppb O 2eq On Thursday 30 st of August purity was compatible with ~60 us Anode signal Cathode signal ProtoDUNE-SP: On Friday 31 st of August, 2018 the purity of the bulk liquid argon dropped from 40 us purification cartridges needed to be regenerated. Regeneration took till the 3 rd of September. Filling restarted immediately after. 12 Filippo Resnati - DUNE Collaboration Meeting - CERN - 28 th January 2019
Monitoring LAr Purity During Operation Relative lifetime uncertainty only Purity drops (dips) during ProtoDUNE-SP operation caught by purity monitors. Reasons of purity drops include recirculation pump stoppages, false alarms, and problems from the cryostat-level gauges 13
Purity from PrMs as benchmark for cryogenic operation and recirculation studies 14
Lifetime for TPC calibration Purity Monitor TPC Cathode Anode Cathode • Cosmic rate is low in DUNE FD, and cosmic ray based TPC calibration needs to add up many cosmic ray runs taken at different periods à Choose TPC cosmic runs under same PrM purities for e-lifetime calibration • PrM-TPC combined lifetime measurement 15
2. Is the purity stratification observed within the ProtoDUNE-SP cryostat real and if so, is this consistent with initial purity measurements from cosmic rays? • See hints of purity stratification: Purities measured by PrMs are different at different heights. Purities became more consistent when pump and venting stopped. • But, still need to cross calibrate systematic differences between PrMs to confirm if stratification is real. For ProtoDUNE-SP, the calibration will be done in the long vacuum tube in ENH1@CERN when we pull the three purity monitors out to prepare for ProtoDUNE run-2 • The small statistic uncertainty give PrMs potential to make stratification with high precision, see answers to Q3. • TPC lifetime measurements affected by statistics, space charge effects and other non-uniformity issues, therefore, until now ProtoDUNE-SP TPC hasn’t provided consistent electron lifetime measurements, and there is no purity stratification measurement reported from TPC • There are people considering alternative ways of generating free electrons such as UV LEDs in a photocathode or radioactive sources. These would allow movable devices and reduce the systematics of the stratification measurements 16
Lifetime with 1-sigma band for absolute (overall) uncertainty Hints for e-lifetime stratification Absolute uncertainty 5-13% in lifetime at ~7ms, dominated by transparency correction and anode/cathode gain correction Gain uncertainty can be calibrated in vacuum à Will do so when we pull PrM Assembly out to prepare for protoDUNE-SP run2 Transparency correction uncertainty can be prevented if we have longer purity monitors 17
Lifetime for Cryogenic System Studies PrMs are sensitive to purity change Typically no regular TPC data when testing recirculation reduced pump speed All boil-off filtered pump off All boil-off vented pump off All boil-off GAr condensed and returned Pump restart P1 P2 P3 P4 P5 Mar 12, 2019 Ilsoo Seong 18
Lifetime Ratio compared with Mid PrM • When the pump was off (no flow), the lifetime difference getting smaller pump off pump off All boil-off GAr All boil-off condensed vented and returned pump stop P1 P2 P3 P4 P5 Ilsoo Seong 19
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