# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### LArIat
Initially, the cathode consisted of a single copper plate, but towards the end of operation this was replaced by a stainless steel mesh-acting as a prototype for the cathode that has now been installed in SBND. The cathode bias is provided by a HV feedthrough of similar design to that used by ICARUS T600, and was set at \(-\)23.5 kV [40]. The outer walls of the TPC also double as the mounting points for the field-shaping elements-constructed out of 1 cm wide copper strips with a 1 cm centre-to-centre spacing, as shown in Figure 18. As with previously discussed field cages, the drift field is created through the use of a resistor chain attached to the field cage elements. All four sides of the field cage are covered by TPB-coated reflective foils, to wavelength-shift the VUV scintillation light to visible wavelengths that can be observed by the LArIAT PDS (described below). The same foils were also mounted onto the cathode [40]. Figure 17: **(Left)** The Liquid Argon In A Testbeam (LArIAT) cryostat, prior to relocation into the Fermilab Test Beam Facility. The beam window on the outer upstream end-cap can be seen, as well as the flange connected to the PDS located on the cylindrical side, and various other off-detector hardware such as scroll pumps for the vacuum jacket and components of the LAr recirculation system. **(Right)** The interior of the cryostat, showing the position of the TPC within the inner vessel, and the cold front-end electronics boards connected to the wire-based APA. Both taken from [40]. The APA of LArIAT consists of three wire planes, although only two of them were actually used for charge readout. The closest plane to the cathode is the \"shield\" plane-comprised of wires that are vertically orientated, but not read out. Moving outwards, this is followed by one induction plane and the collection plane, with wires orientated at \(+60^{\circ}\) and \(-60^{\circ}\) to the vertical respectively [40]. (From a purely geometric standpoint, two 2D views is indeed enough to fully reconstruct the three-dimensional particle track, but the addition of a third view, as in other experiments' wire-based charge readouts, greatly increases the reconstruction performance and precision.) The wire spacing in all three planes was set at 4 mm during much of LArIAT's operation, with the biases being \(-298\) (shield), \(-18.5\) (induction) and \(+338\) V (collection). Towards the end of the data-taking period, the spacing was changed to 5 and then 3 mm, necessitating corresponding changes in the biases in order to ensure that 100% of the drifted electrons still pass through both the shield and induction planes [40]. These alternate setups were used to test the effect of wire spacing on the overall performance of the experiment, so as to inform future LArTPC design. The signals from the 480 wires are first passed to 10 front-end electronics boards mounted on the side of the TPC, i.e., within the cryogenic environment. The ASICs on these boards perform initial amplification and digitisation of the signals (as well as providing bias to the individual wires) [40], before they are sent through the single feedthrough on the top of the cryostat to the warm electronics mounted on the external side of the flange. Additional amplification and noise cancellation is performed here, and the signals are then carried to the array of digitisers situated 8 m from the detector vessel [40]. This distance is required to ensure that charged particles from the beam do not pass through the electronics, which would otherwise result in considerable noise being introduced. As with the wire planes, the LArIAT PDS--shown in Figure 19--was used not just for data collection, but also to evaluate various hardware and design configurations throughout the experiment's operation time.