# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### ProtoDUNE-SP
The majority (58) of these are acrylic lightguides, with half of them featuring a \"dip-coated\" design (where each light guide is dipped in a liquid coating containing TPB) and the other half using a \"double-shift\" approach (in which the acrylic is both covered in TPB-impregnated plates and also doped with a secondary wavelength shifter). The two remaining PDS modules are based on the ARAPUCA technology. An example of the module positioning in one APA is shown in Figure 28. The devices are all read out using silicon photosensors, with three models in use across the 60 PDS modules [51], and the signals from these sensors are carried out of the cryostat via the signal feedthroughs, as shown previously in Figure 27. The PDS has undergone extensive commissioning, calibration and operation (details of which can be found in [51]), but it has been found that the ARAPUCA modules out-performed both types of lightguides as well as the required specifications for the DUNE-SP PDS-showing excellent collection efficiency, a high photon yield (that is, the number of detected photons per MeV of deposited energy), time resolution on the order of a few tens of nanoseconds, and linear behaviour across a wide range of incident particle energies. The entire detector assembly described above is housed in a 11.404 \(\times\) 11.404 \(\times\) 10.756 m membrane cryostat [48]. This type of cryostat-also used at SBND, as previously noted-has a long history of use in the transport and storage of liquefied natural gas, and is particularly suited for extremely large cryogenic vessels. The ProtoDUNE-SP cryostat consists of a steel warm outer structure enclosing two membranes (one made of stainless steel and the other of an aluminium composite) and multiple insulation layers. Dedicated penetrations through the cryostat walls are used for the beam plug, which allows incoming particles to travel unimpeded into the active LAr volume, and the LAr extraction pipe that forms part of the purification system (described below). The detector itself is mounted onto a \"detector support structure\" (previously shown in Figure 26), which is attached to and mechanically supported by the outer cryostat structure [48]. A system of cosmic ray taggers is positioned on the upstream and downstream faces of the cryostat (through which the beam enters and exits the detector respectively). These are built from plastic scintillator, and allow the tagging of not only cosmic muons, but also the \"halo\" muons originating from the beam's production target. Due to ProtoDUNE-SP's location at surface level, there is a relatively large cosmic muon flux, and this large population of events has been used as part of the detector calibration studies [48]. Figure 27: A schematic view of the APA readout electronics in ProtoDUNE-SP. Front-end motherboards, 20 of which are mounted on each APA, collect the wire signals and pass them to the WIECs mounted on the external sides of the cryostat feedthroughs. Wire biases and connections to and from the PDS are also provided through the feedthroughs. An identical scheme is anticipated to be used by DUNE-SP. Adapted from [48]. The cryogenics systems used by ProtoDUNE-SP [48] have been developed in concert with efforts for ProtoDUNE-DP, SBND and ICARUS T600, as they broadly share very similar requirements and specifications. This common approach allows for the pooling of resources and expertise, and will lead to a standardisation of methods and designs, reducing the cost and time that might be otherwise incurred across all four projects. Parts of the ProtoDUNE-SP system-specifically, the commercial provision and onsite storage of liquid argon and nitrogen-are shared with ProtoDUNE-DP due to their close proximity at the CERN North Area.