Purity monitors some considerations for DUNE Jianming Bian (UCI) - - PowerPoint PPT Presentation

Purity monitors — some considerations for DUNE

Jianming Bian (UCI) Andrew Renshaw (Houston) Laura Manenti (UCL) Apr 17, 2018

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 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

• M. Adamowski et al., JINST 9, P07005 (2014).

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Purity Monitor (PrMon) System Description

PrMon PrMon Fron-End HV/LV Power Supplies Xe Flash Lamp PC Running LabVIEW Waveform Digitizer The PrMon front-end decouples the signal from the HV and amplifies it before sending it along to the digitizers LabVIEW-based analysis on digitized waveforms, and program also controls hardware

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24 V Power Source

PrMon System Components: Equipment

Phoenix Contact QUINT4- PS/1AC/24DC/5 Hamamatsu product, see slide 6 for details 1 Wiener MPOD mini-crate (4 slots) mixed HV/LV located in electronics rack containing:

• 1 EHS 8205n or 8205n-F module (F means

single channel floating ground)

• 1 EHS 8260p or 8260p-F module
• 1 MPV 8016D module

Custom electronics in NIM bin on top of cryostat next to flange, see slide 7 For details Windows PC at electronics rack with NI USB-600X device for IO 3 Alazar ATS-310-8M PCI Digitizers in PCI extension box, located at electronics rack next to PC

PrMon PrMon Fron-End HV/LV Power Supplies Xe Flash Lamp PC Running LabVIEW Waveform Digitizer

SHV coaxial cable with SHV connectors

• n both ends

(~2 m long) Coaxial cable selected by CERN (RG-58 OK) LEMO/BNC connectors (~20 m long) Waveforms from PCI extension box to PC via serial cable Cable selection by CERN, LV cable terminated at NI USB-600X device and at flash lamp external trigger (~20 m long) Xe flash delivered to PrMons via optical fiber fed-thru cryostat flange Cable selection by CERN, 3 LV cables terminated at NI UBS- 600X device and at power supplies (few meters long) 4

24 V Power Source

PrMon System Components: Cables

SHV coaxial cable with SHV connectors

• n both ends

(~20 m long) LV cable terminated at NIM bin and power supply (~20 m long) Cable selection by CERN, LV cable terminated directly to 24 V supply and flash lamp supply (possibly ~20 m long)

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
• n the gold surface, so the purity monitor can keep running over long

periods in the cryostat

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Jianming Bian - DPF2015

Photocathod Degradation (Longevity of Purity Monitors)

Photocathode before LAr Running Photocathode after LAr Running at LAPD

Elements on the surface of photocathodes LAPD PrM signal

• rganic compound？

Photocathode degradation could significantly worsens a purity monitor's signal during long-term use.

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.

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Metal Box Xenon flashlamp Main Discharge Capacitor Power supply 0.3-1kV 24V DC Red: Voltage input line Green: Voltage return line (referece) Black: Shielding grounding line Controlled by Slow control syst.

Flash Lamp: Cartoon Schematic

All equipment here is commercially bought

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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

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• 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)

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

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