Purity monitors — some considerations for DUNE Jianming Bian (UCI) Andrew Renshaw (Houston) Laura Manenti (UCL) Apr 17, 2018
Purity Monitor (PrMon) System Description Individual PrMon: Xe flash lamp light source • Al-Ti-Au photocathode for • drift electron generation Cathode/anode gates for • charge screening at readout Internal cable shields tied • to PrMon cage and flange M. Adamowski et al., JINST 9, P07005 (2014). Vertical string inside cryostat placed on each end of Cryostat, cable shields attached to cryostat ground The individual purity monitors will be assembled into two strings at different heights All three PrMon cages attached to ground via flange 2
PrMon System Components: Equipment Custom electronics in NIM bin on top of cryostat next to flange, see slide 7 For details 1 Wiener MPOD mini-crate (4 slots) mixed HV/LV HV/LV located in electronics rack containing: PrMon PrMon Power 1 EHS 8205n or 8205n-F module (F means • Fron-End Supplies single channel floating ground) • 1 EHS 8260p or 8260p-F module 1 MPV 8016D module • The PrMon front-end 3 Alazar ATS-310-8M PCI Digitizers Waveform decouples the signal from in PCI extension box, located at Digitizer electronics rack next to PC the HV and amplifies it before sending it along to the digitizers 24 V Power Xe Flash PC Running LabVIEW-based analysis on Source Lamp LabVIEW digitized waveforms, and program also controls Phoenix Contact Hamamatsu Windows PC at hardware QUINT4- product, see slide electronics rack with NI PS/1AC/24DC/5 6 for details USB-600X device for IO 3
PrMon System Components: Cables SHV coaxial cable SHV coaxial cable with SHV connectors with SHV connectors on both ends on both ends (~20 m long) (~2 m long) HV/LV PrMon PrMon Power Fron-End Supplies LV cable terminated at NIM bin and Coaxial cable selected by CERN (RG-58 OK) LEMO/BNC connectors power supply (~20 m long) (~20 m long) Waveform Xe flash delivered to PrMons via optical fiber Digitizer fed-thru cryostat flange Waveforms from PCI extension box to PC via serial cable 24 V Power Xe Flash PC Running Source Lamp LabVIEW Cable selection by CERN, 3 LV cables terminated at NI UBS- 600X device and at power Cable selection by CERN, LV Cable selection by CERN, LV cable supplies (few meters long) cable terminated directly to 24 terminated at NI USB-600X device V supply and flash lamp supply and at flash lamp external trigger (possibly ~20 m long) (~20 m long) 4
Degradation • Caused by operating purity monitors in impure liquid argon or argon gas • Interlock to prevent purity monitor running at very low purity • Increase light intensity (signal) to reduce effect • Have at least one purity monitor inline with the cryogenics purification system and have them valves so they can be maintained over time • Run flash light with high frequency can partially recover the cathode • Use a heating method to repair photocathode degradation caused by water on the gold surface, so the purity monitor can keep running over long periods in the cryostat 5
Photocathod Degradation ( Longevity of Purity Monitors ) Photocathode degradation could significantly worsens a purity monitor's signal during long-term use. organic compound ？ Elements on the surface of photocathodes Regn1: Title 16K Photocathode before LAr Running 14K Au 4f 12K LAPD PrM signal 10K COUNTS 8K 6K O 1s I 3d5 C 1s 4K 2K 1,100 1,000 900 800 700 600 500 400 300 200 100 0 BINDING ENERGY - EV Regn1: Title Photocathode after LAr O 1s Au 4f 5.5K 5K Running at LAPD 4.5K I 3d5 F 1s 4K 3.5K C 1s COUNTS 3K Si 2s 2.5K 2K 1.5K 1K 500 Jianming Bian - DPF2015 1,100 1,000 900 800 700 600 500 400 300 200 100 0 BINDING ENERGY - EV
Noise • Light leakage from purity monitor à PDS • From the flash lamp • Electronic noise in cold electronics à TPC • Majorly caused by the current surge in the discharging process of the main capacitor of the purity monitor xenon light source when producing a flash. 7
Flash Lamp: Cartoon Schematic Metal Box All equipment here is commercially bought Xenon flashlamp Main Discharge Red: Voltage input line Capacitor Green: Voltage return line ( referece ) Black: Shielding grounding line Power supply 0.3-1kV 24V DC Controlled by Slow control syst. 8 Ext Trigger
Noise • The flash it self is a few microsecond, much shorter than the millisecond TPC+PDS trigger window. Flash rate ~ 10 Hz • As long as it doesn't flash during the trigger window (PDS+TPC), there will be no significant noise • Set up a programmable pulse generator to trigger the xenon flash lamp • Dedicate a part of the inter-spill time to this in which we will veto triggers (Giovanna) • Whenever we detect the “pulse” from the PDS or TPC trigger, the pulse generator will not send a trigger to the xenon flash lamp (via a “AND” operation in the pulse generator) 9
Precision of purity monitor • Dominated by the fluctuation of the signal • Measurement of the precision: measure width of the QA/QC distribution vs. height of cathode signal • In Vacuum and argon gas UCI lab • In liquid argon à protoDUNE • Increase the light intensity (signal) can reduce fluctuation, 35t/MicroBoone use 3 fibers à add to 8 fibers • Optimize number of flashes per measurement • Drift time can be tuned by changing HV of purity monitor • Simulation, systematic errors etc 10
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