The XENON1T liquid level measurement system

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Doris Hart
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1 The XENON1T liquid level measurement system Christopher W. Geis on behalf of the XENON collaboration Johannes Gutenberg-Universität Mainz DPG Frühjahrstagung /15

2 Introduction Why is a liquid level measurement in an LXe TPC needed? Cryostat - understanding the size of proportional scintillation signal Liquid Level - monitors level stability inside - Alignment of the TPC vertical axis with the liquid level normal. Long Level Meters (LLM): 1.5 m - 4 capacitive SLMs provide redundant leveling information (sub mm) Liquid Level outside 5mm Short Level Meters (SLM): Bell TPC - 2 capacitive LLMs monitor TPC filling process - measuring and monitoring the liquid xenon level Top outside the bell 2/15

3 The XENON1T TPC Anode +5 kv & Gate (GND) (located inside the bell) Cryostat Long Level Meter PTFE support pillars Short Level Meter Field shaping rings Cathode -100 kv TPC Top Ring Bottom 3/15

Short Level Meter Design - Different designs possibilities

5 mm Space between plates: d = 1 mm - Test with 15m coax cable

4 Short Level Meter Design - Different designs possibilities simulated (COMSOL) Design Choice: Triple plate capacitor with outer shield CGXe = 16.5 pf, CLXe = 26.9 pf Material: OFE Copper C/h = 1.04 pf/mm Plate thickness: 0.5 mm Space between plates: d = 1 mm - Test with 15m coax cable in LN2 Linear capacitance decrease proportional to liquid level Top Electrostatic simulation 4/15

5 Long Level Meter Design - Different designs possibilities simulated (COMSOL) Design Choice: Electrostatic simulation Double cylindric capacitor CGXe = pf, CLXe = pf Material: Stainless steel C/h = 0.09 pf/mm Sliding fixation to account for TPC shrinking Outer Electrode Inner Electrode Liquid Inlet Dimensions: h = 1357 mm, R = 3 mm, r = 1.5 mm Pipe wall thickness d = 0.3 mm Top 5/15

distance: Strain Relief Installed SLM with

6 Short Level Meter Installation - Installation of short level meters in October 2015 in cleanroom Top Ring SLM - Four level meters distributed at 90 distance: Strain Relief Installed SLM with open bell TPC top ring top view Top Covered SLM with closed bell 6/15

7 Long Level Meter Installation Contact Screws / Cu plates - Installation of long level meters in Nov 2015 in cleanroom inside XENON1T water tank Fixation on TPC bottom - Two level meters distributed at 180 distance: LLM Top with connected signal cables TPC top ring top view 7/15

8 Readout Principle Readout based on the UTI (Universal Transducer Interface) chip by Smartec (Failing) classical way of measuring capacitors Two-Port UTI approach (measuring Cx only) 1 Full UTI measurement cycle - In classical capacitance measurements one always measures C = C x + Cp Tref already C = O(nF) Problems if Cx = O(pF) T but off 10m coax cable have p - UTI chip uses two-port approach with four-poles Excitation voltage at Out and virtual mass of charge amplifier at In Cp1 and Cp2 have no influence - Collected charge at In controls excitation frequency of internal RC oscillator C x ~ 1/f - Frequency divider gives digital output of UTI for all measured capacitances 8/15

Readout Principle Measurement sequence: 1 Full UTI measurement cycle Toff Tref Tx Toff duration of offset phase, Tref duration of reference phase, Tx duration of measurement phase 1.

9 Readout Principle Measurement sequence: 1 Full UTI measurement cycle Toff Tref Tx Toff duration of offset phase, Tref duration of reference phase, Tx duration of measurement phase 1. UTI chips charge/discharge capacitors 3 different phases 2. Microcontroller captures number of processor cycles within each UTI phase: N off, Nref, Nx 3. with known reference capacitance Cref: 9/15

10 Readout Electronics Schematic 1. Measurement request every second Micro Controller UTI LLM UTI Readout Scheme... UTI RS485 Transceiver UTI UTI TPC 3. Once all UTIs have been measured Transmission of values over the RS485 bus UTI UTI SLM 2. All UTIs measured sequentially by multiplexer } for possible additional level meters or replacement RS485 Slow Control Bottom 10/15

11 Readout Electronics Multiplexer PIC microcontroller (Assembler Code) Power Supply RS485 Bus Port UTI's With support of the PRISMA detector lab (A. Brogna) 11/15

12 Readout Tests SLM Resolution: ~0.02 pf corresponds to spatial resolution of ~20 µm LLM Resolution: ~0.2 pf corresponds to spatial resolution of ~2mm Bottom Problem identified with SLM1 (half capacitance), does not prevent using it as a level meter 12/15

13 Power-on-Stability Several measurements done under same conditions after different power on actions SLM Power-on-Stability: ~0.001 pf Deviation of 0.01 % Bottom stable Levelmeter system extremely LLM Power-on-Stability: ~0.01 pf Deviation of 0.01 % 13/15

14 Summary & Outlook Summary: - The XENON1T liquid level will be measured by 4 small and 2 long level meters - SLMs: Triple-plated: C/h = 1.04 pf/mm - LLMs: Double-cylindric: C/h = 0.09 pf/mm - The level meter system was installed during the TPC construction phase in Oct/Nov Readout electronics based on a self-made PCB and microcontroller based readout sequence - In situ data taking allows the following resolutions - SLMs: R = ~20 µm - LLMs: R = ~2 mm Outlook: - Test of level meter performance in final HV environment (HV switched on for PMTs, meshes, etc...) - Liquid Xenon filling upcoming Calibration of level meters in LXe and comparison to simulation - The SLM will be used to level the TPC even before the first S2 signals are measured 14/15

15 Thank you! Questions? Top Bottom 15/15

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