Liquid Argon Purity Research Articles

Current and future challenges when operating the ATLAS Liquid Argon Calorimeter

The Liquid Argon (LAr) Calorimeters are employed by ATLAS for precision electromagnetic calorimetry and for hadronic and forward calorimetry. They also provide inputs to the first level of the ATLAS trigger system.The LAr Calorimeters have been operated during regular ATLAS data taking since 2008. All critical parameters, like LAr purity and temperature, have been kept at stable values resulting in reliable signal pulses. In 2022, the LHC collider has increased the luminosity leading to a pile-up of up to 70 interactions per bunch crossing. In the high luminosity phase, HL-LHC, planned to be fully functional in 2029, the pile-up will increase up to 200 interactions per bunch crossing.This contribution will highlight the present and future challenges in the operation of such a detector.

Observation of radon mitigation in MicroBooNE by a liquid argon filtration system

The MicroBooNE liquid argon time projection chamber (LArTPC) maintains a high level of liquid argon purity through the use of a filtration system that removes electronegative contaminants in continuously-circulated liquid, recondensed boil off, and externally supplied argon gas. We use the MicroBooNE LArTPC to reconstruct MeV-scale radiological decays. Using this technique we measure the liquid argon filtration system's efficacy at removing radon. This is studied by placing a 500 kBq 222Rn source upstream of the filters and searching for a time-dependent increase in the number of radiological decays in the LArTPC. In the context of two models for radon mitigation via a liquid argon filtration system, a slowing mechanism and a trapping mechanism, MicroBooNE data supports a radon reduction factor of greater than 97% or 99.999%, respectively. Furthermore, a radiological survey of the filters found that the copper-based filter material was the primary medium that removed the 222Rn. This is the first observation of radon mitigation in liquid argon with a large-scale copper-based filter and could offer a radon mitigation solution for future large LArTPCs.

Purity monitoring for ProtoDUNE-SP

The Deep Underground Neutrino Experiment is a next-generation long-baseline neutrino oscillation experiment based on liquid argon time projection chamber technology. DUNE-s single-phase prototype ProtoDUNE-SP at CERN finished its two-year Phase-1 running in July 2021, successfully collected test-beam and cosmic ray data. A key aspect of LArTPC calibration is the lifetime of drift electrons. A purity monitor is a miniature TPC measuring the lifetime of electrons generated from the photocathode via the photoelectric effect. It enables continuous monitoring of the detector status, especially when filling the cryostat and when liquid argon recirculation systems operate. The purity monitoring system in ProtoDUNE-SP Phase-1 monitored liquid argon purity throughout its entire lifetime. It is essential to the experiment’s successful commissioning, operation, and data taking. This poster discusses the design, implementation, and results of purity monitors and plans.

Performance of different photocathode materials in a liquid argon purity monitor

Purity monitor devices are increasingly used in liquid noble gas time projection chambers to measure the lifetime of drifting electrons. Purity monitors work by emitting electrons from a photocathode material via the photoelectric effect. The electrons are then drifted towards an anode by means of an applied electric drift field. By measuring the difference in charge between the cathode and the anode, one can extract the lifetime of the drifting electrons in the medium. For the first time, we test the performance of different photocathode materials—silver, titanium, and aluminium—and compare them to gold, which is the standard photocathode material used for purity monitors. Titanium and aluminium were found to have a worse performance than gold in vacuum, whereas silver showed a signal of the same order of magnitude as gold. Further tests in liquid argon were carried out on silver and gold with the conclusion that the signal produced by silver is about three times stronger than that of gold.

The new front end and DAQ of the ICARUS detector

ICARUS is the largest imaging LAr TPC ever operated. During its LNGS run on the CNGS neutrino beam, from 2010 to 2013, produced some thousands neutrino events of unprecedented quality. This was possible thanks its mechanical precision and stability, liquid argon purity and electronics front-end and DAQ. Actually ICARUS T600, in view of its operation at FNAL on the SBN neutrino beam, is undergoing a major overhauling that implies cathode mechanics improvement, additional PMTs installation and a new electronics front-end and DAQ. This electronics implements a new architecture, integrated onto the flange proprietary design, and a new front-end that improves S/N and induction signals treatment. This issue will be presented in detail together with data recently recorder at CERN in the FLIC, 50 litres, LAr facility.

Design and operation of LongBo: a 2 m long drift liquid argon TPC

In this paper, we report on the design and operation of the LongBo time projection chamber in the Liquid Argon Purity Demonstrator cryostat. This chamber features a 2 m long drift distance. We measure the electron drift lifetime in the liquid argon using cosmic ray muons and the lifetime is at least 14 ms at 95% confidence level. LongBo is equipped with preamplifiers mounted on the detector in the liquid argon. Of the 144 channels, 128 channels were readout by preamplifiers made with discrete circuitry and 16 channels were readout by ASIC preamplifiers. For the discrete channels, we measure a signal-to-noise (S/N) ratio of 30 at a drift field of 350 V/cm. The measured S/N ratio for the ASIC channels was 1.4 times larger than that measured for the discrete channels.

The ICARUS T600 Liquid Argon Purification System

The ICARUS detector is a liquid argon time projection chamber with unique features that make it an ideal device to be used for several particle physics applications. After years of R&D activities, the ICARUS Collaboration proposed the construction of the T600 in strict partnership with industry to guarantee the necessary and viable scaling-up of the technology from prototypal dimensions to sized plants in order to study neutrino oscillations and matter stability in an effective way. The T600 represents the largest LAr detector (760 t LAr mass) ever realized. It was installed and successfully operated for 3 years inside the underground Gran Sasso Laboratory from May 2010 to June 2013. One of the most important issues for the success of the detector technology is the liquid argon purity. Purity requirements become stronger and stronger with the increase of the detector dimensions: for a plant of the ICARUS T600 size it is necessary to keep the residual electronegative impurity content to a level of the order of 0.1 parts per billion or better all over the argon volume during the whole detector run, thus allowing the ionization tracks, created by interacting particles inside LAr, to be transported with only slight attenuation along the drift path. In this paper we present the ICARUS T600 purification plant installed at Gran Sasso Laboratory and describe in details the solutions adopted for the LAr re-circulation and purification systems that permitted to reach impressive results in terms of LAr purity thus representing a milestone for any project involving LAr and developments at higher LAr mass scale.

The Liquid Argon Purity Demonstrator

The Liquid Argon Purity Demonstrator was an R&D test stand designed to determine if electron drift lifetimes adequate for large neutrino detectors could be achieved without first evacuating the cryostat. We describe here the cryogenic system, its operations, and the apparatus used to determine the contaminant levels in the argon and to measure the electron drift lifetime. The liquid purity obtained by this system was facilitated by a gaseous argon purge. Additionally, gaseous impurities from the ullage were prevented from entering the liquid at the gas-liquid interface by condensing the gas and filtering the resulting liquid before returning to the cryostat. The measured electron drift lifetime in this test was greater than 6 ms, sustained over several periods of many weeks. Measurements of the temperature profile in the argon, to assess convective flow and boiling, were also made and are compared to simulation.

First operation and performance of a 200 lt double phase LAr LEM-TPC with a 40 × 76 cm2 readout

In this paper we describe the design, construction, and operation of afirst large area double-phase liquid argon Large Electron MultiplierTime Projection Chamber (LAr LEM-TPC). The detector has a maximumdrift length of 60 cm and the readout consists of a 40 × 76 cm2 LEM and 2D projective anode to multiply and collectdrifting charges. Scintillation light is detected by means ofcryogenic PMTs positioned below the cathode. To record both chargeand light signals, we have developed a compact acquisition system,which is scalable up to ton-scale detectors with thousands of chargereadout channels. The acquisition system, as well as the design andthe performance of custom-made charge sensitive preamplifiers, aredescribed. The complete experimental setup has been operated for afirst time during a period of four weeks at CERN in the cryostat ofthe ArDM experiment, which was equipped with liquid and gas argonpurification systems. The detector, exposed to cosmic rays, recordedevents with a single-channel signal-to-noise ratio in excess of 30 forminimum ionising particles. Cosmic muon tracks and theirδ-rays were used to assess the performance of the detector, andto estimate the liquid argon purity and the gain at differentamplification fields.

Results from the Fermilab Materials Test Stand and Status of the Liquid Argon Purity Demonstrator

The Fermilab Materials Test Stand was developed to test the suitability of materials for use in large liquid argon time projection chambers (TPCs). In addition to determining which materials are viable for use in TPCs, the test stand has also shown that water is especially detrimental to maintaining long electron lifetimes. The Liquid Argon Purity Demonstrator is currently under construction at Fermilab. Its goal is to show that long electron lifetimes can be achieved without evacuation of the cryostat, which is of particular interest in designing large liquid argon TPCs.

Analysis of the liquid argon purity in the ICARUS T600 TPC

The results reported in this paper are based on the analysis of the data recorded with the first half-module of the ICARUS T600 liquid argon Time Projection Chamber (LAr TPC), during a technical run that took place on surface in Pavia (Italy). We include results from the linearity, uniformity and calibration of the electronics, measurements on the electron drift velocity in LAr at different electric fields, as well as the LAr purity achievement of the detector. Two complementary techniques were used to measure the drift electron lifetime inside the active volume: the first, from the data of a purity monitor, gives a measurement localized in space; the second, based on the study of the signals produced by long minimum ionizing tracks crossing the detector, provides a LAr volume averaged value. Both methods yield consistent results over the whole data taking period and are compatible with an uniform LAr purity over the whole volume. The maximal drift electron lifetime value was recorded before the run stop and was about 1.8 ms . From an interpretation of the observed drift electron lifetime as a function of time, we conclude that the adopted technology would allow for drift distances exceeding 3 m .

A purity monitoring system for the H1 liquid argon calorimeter

The ionization probes used for monitoring the liquid argon purity in the H1 calorimeter are described and results of their operation in tests at CERN and during the period 1992 to the end of 1998 at HERA are given. The high sensitivity of the charge measurements leads to refined charge collection models, and to the observation of a variation of the ionization yield of our electron sources with temperature.

Response of an [formula omitted] source mounted in a liquid argon ionization cell and read out in full charge collection mode

The total charge response curve of an 241 Am source placed in a liquid argon ionization cell has been measured. In a pure liquid argon sample (O 2 concentration <0.1 ppm), it can be described by a semi-empirical formula which is derived from a model formerly elaborated by Thomas and Imel. The validity of this new formula was also tested in the case of oxygen-polluted liquid argon. The agreement with the data seems to indicate that the initial ion–electron pair recombination factor is not affected when the O 2 concentration is smaller than 7 ppm. Further use of our recombination factor parameterization has been made to analyze data of liquid argon purity monitors utilizing 241 Am sources with a sensitivity to O 2 concentrations of ∼0.1 ppm.

Long Distance Drifting of Ionization Electrons in Liquid Argon

As part of our continuing program to develop a liquid argon Time Projection Chamber (TPC), we have drifted ionization electrons produced by a 113Sn internal conversion electron source over a physical distance of 20 cm in fields of 0.8 to 1.6 kV/cm. This liquid purity was maintained over a period of many days. The liquid argon purity has been improved in the liquid state by the use of molecular sieves.