# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### ProtoDUNE-SP  
With an active TPC volume measuring 6 \(\times\) 7 \(\times\) 7.2 m and containing 411 tonnes of LAr [48], the ProtoDUNE-SP detector is only a fraction of the size of one DUNE far detector module, but nevertheless it is currently the largest single-volume LArTPC ever operated (remembering that the 476 tonnes of LAr at ICARUS T600 are split across two separate volumes). Since late 2018, ProtoDUNE-SP has been in operation at the H4-VLE (\"Very Low Energy\") beamline located in the CERN North Area, receiving \(e^{-}\), \(\mu^{\pm}\), \(\pi^{\pm}\) and \(p\) at momenta ranging from 0.5 to 7 GeV/c [49]. Figure 26: The ProtoDUNE-SP LArTPC, with key components labelled. Taken from [48]. Figure 26 shows the layout of the ProtoDUNE-SP TPC. The detector effectively operates as half of DUNE-SP-with two, rather than four, back-to-back drift volumes of 3.6 m width sharing a common set of CPA sections. As discussed above, the ProtoDUNE-SP CPA sections (previously shown in Figure 23 (left)) are identical in design and manufacturing to those to be used in DUNE-SP, but ProtoDUNE-SP uses three such sections placed side by side-for a total of 18 1.2 \(\times\) 2 m Kapton-laminated FR4 RP elements arranged in a 6 \(\times\) 3 grid [48]. The drift field is provided via the same field cage assemblies depicted in Figure 23 (right), and both the nominal cathode bias (\(-\)180 kV) and the drift field (500 V/cm) match the design values for DUNE-SP [48]. Each of ProtoDUNE-SP's \"APA faces\" consists of three of the 6 \(\times\) 2.3 m APAs previously shown in Figure 25 arranged side by side (labelled as \"APA #1\", \"APA #2\" and \"APA #3\" for the detector face shown in Figure 26), with the four wire planes biased at \(-\)665 (shielding plane G), \(-\)370 (induction plane U), 0 (induction plane V) and +820 V (collection plane X). It is of course clear that the double-sided sensitivity of the DUNE-SP APAs is not required in ProtoDUNE-SP, but the complete assemblies are nonetheless used so as to validate the design under full operating conditions, and to save on the cost and time of manufacturing dedicated single-sided APAs for ProtoDUNE-SP. The presence of the unused side of wire planes also in fact aids the detector, by collecting and blocking any ionisation occurring outside the TPC from entering [48]. Signals from the combined 15,360 readout wires are carried out of the TPC via the same system of electronics envisioned for DUNE-SP: a series of front-end motherboards mounted on the APAs gather signals from 128 wires each (with 20 motherboards per APA), and cryostat feedthroughs act as the interface between the cold and warm electronics [48]. This is illustrated schematically in Figure 27. The entire electronics system has undergone a detailed and systematic testing and commissioning program during installation and subsequent operation of the ProtoDUNE-SP detector [50], which showed a 99.7% working channel efficiency and higher-than-expected operating performance, with low noise and high signal-to-noise ratios on all three wire planes. This bodes extremely well for the eventual implementation of the much larger DUNE-SP APA readout systems using the same components and methods. The detector as a whole has proved to be more than capable of operating at nominal conditions over long periods, with no instabilities or breakages reported on the cathode or field cage elements, and only a very small number of channels failing during the approximately 18 months of data-taking [51]. As mentioned previously, the choice of hardware to be used in the DUNE-SP PDS has yet to be made, but the ProtoDUNE-SP PDS plays a key part in this by allowing the various devices under consideration to be tested, used and characterised under nominal operating conditions. Each of the six ProtoDUNE-SP APAs can hold ten PDS \"modules\" behind the wire planes, allowing for a total of 60 modules to be installed [51].