# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 3 Dual-Phase Experiments
### WA105 and ProtoDUNE-DP  
Authors' Note: at various points during the dual-phase DUNE program, the two prototype detectors have each been referred to by several different names. The smaller of the two, with dimensions of 3 \(\times\) 1 \(\times\) 1 m, has gone by \"WA105\", \"WA105-DEMO\" and \"WA105-311\". The larger 6 \(\times\) 6 \(\times\) 6 m iteration has previously also been designated \"WA105\", as well as \"WA105-666\" and \"NP02\", and is now commonly known as \"ProtoDUNE-DP\". Figure 39: A schematic view of the dual-phase DUNE far detector module, with major components labelled. Taken from [74]. For clarity and convenience, in this paper we will use \"WA105\" to exclusively refer to the smaller prototype, and \"ProtoDUNE-DP\" for the larger one. Constructed in 2016, the WA105 experiment (so called due to its location at CERN's \"West Area\") is the first of two detectors dedicated to assessing the scalability of the dual-phase LArTPC concept-that is, if a DUNE far detector based on this design could be assembled and operated successfully. To that end, WA105 features a 3 \(\times\) 1 \(\times\) 1 m TPC [78] enclosed by a 1 m thick membrane cryostat constructed from layers of glass-reinforced polyurethane foam (for thermal insulation) and plywood (for pressure distribution). The TPC field cage, containing \(\approx\)4.2 tonnes of LAr, is suspended from the 1.2 m thick top-cap of the cryostat, as shown in Figure 40.  
At the bottom of the WA105 field cage is the cathode-a metallic grid nominally biased at \(-\)50 kV via a dedicated HV feedthrough [78]. This feedthrough has also been successfully operated at \(-\)300 kV, in order to test the design for eventual use in the larger ProtoDUNE-DP detector. The 1 m tall field cage consists of 20 field-shaping elements positioned at 5 cm intervals above the cathode, with the drift field being produced by a resistor chain attached to the field-shaping elements. In order to detect the prompt scintillation light for the purposes of event triggering and absolute \(z\)-positioning, 5 8-inch diameter Hamamatsu R5912-MOD PMTs are positioned below the cathode-three of which are directly coated with TPB, with the remaining two operating in conjunction with TPB-coated acrylic discs [79]. The 3 \(\times\) 1 m WA105 CRP, shown in Figure 41, consists of the extraction grid, LEM and anode plane as previously described in Section 3. The extraction grid is a single plane of 100 um diameter tensioned wires, with 3.125 mm wire-to-wire spacing in both \(x\) and \(y\) directions, and held 5 mm below the surface of the LAr [78]. In contrast, both the LEM (positioned 5 mm above the LAr surface) and anode plane (2 mm above the LEM) are each assembled from 12 50 \(\times\) 50 cm \"units\", which are electrically connected to form a single continuous plane for each layer. Each of the LEM units-the fine structure of which is shown in Figure 41 (top-right inset)-is a commercially manufactured PCB, with holes of 500 um diameter (with an additional 40 um dielectric rim to reduce the risk of electrical breakdown) and 800 um \"pitch\" (centre-to-centre hole spacing). These characteristics have been decided upon following a series of performance tests conducted on a variety of LEM designs [80]. The extraction and amplification fields are 2 and 30 kV/cm respectively [78]. Each anode  
Figure 40: A model of the WA105 dual-phase LArTPC, showing the field cage suspended from the 1.2 m thick cryostat top-cap, as well as the various feedthroughs that penetrate through to the interior. The inset shows the structure of the charge readout plane (CRP), described in more detail in the main text. Taken from [78]. plane unit-which are also commercially produced PCBs-consists of two layers of 3 mm wide strips arranged so as to produce unambiguous 2D (\(x\) and \(y\)) position reconstruction of the electrons incident from the LEM.