# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 3 Dual-Phase Experiments
### WA105 and ProtoDUNE-DP
Although commercial HV power supplies that provide this bias are available, transmitting it all the way from the HV port at the top of the ProtoDUNE-DP cryostat to the cathode at the bottom-a distance of more than 8 m-is challenging. Rather than manufacturing a single, monolithic HV feedthrough for this purpose, a mechanically simpler solution is employed: a short feedthrough that uses the same design as that of WA105 (which, as noted previously, has been proven to reliably operate at a bias of \(-\)300 kV) coupled to a \"HV extender\" that effectively lengthens the feedthrough by 6 m [82]. The extender is a simple construction consisting of a conducting core surrounded by an insulator, with \"voltage degrader\" rings installed around the outside. These rings are connected to the outside of the field cage elements, and ensure that the electric field in the region outside the active TPC volume remains at zero. The installed extender is shown in Figure 45. DUNE-DP is envisioned to use an equivalent HV extender to connect its feedthrough and cathode, albeit one that is 12 m long. As an additional concern, the DUNE-DP cathode is  
Figure 42: A schematic depiction of the ProtoDUNE-DP detector, with major components labelled. Taken from [82]. required to operate at a bias of \(-600\) kV, and this has necessitated the development (in collaboration with Heinzinger--the DUNE program's industrial partner in the production and procurement of HV power supplies) of a bespoke external power supply capable of producing such a high voltage, since no such device currently exists commercially [74]. Figure 43: A 3D model of the ProtoDUNE-DP cathode plane, which consists of 4 3 \(\times\) 3 m units. The grid structure is manufactured from three sizes of stainless steel tubing: the external perimeter is constructed from 60 mm diameter circular cross-section pipes, 20 \(\times\) 40 mm oval cross-section pipes make up the internal frame, and fine structure is provided by 12 mm diameter pipes. The dual-phase DUNE far detector’s cathode will use an identical grid design, but scaled up to 80 units making a single 12 \(\times\) 60 m plane. Taken from [82]. Figure 44: A view of the interior of the ProtoDUNE-DP drift volume. The four cathode units can be seen at the bottom, and the field cage (with attached resistor chain elements) is installed on the vertical faces. Taken from [82]. The maximum drift time in ProtoDUNE-DP will be 3.7 us, and a goal of 7 ms electron lifetime has been set [82] (corresponding to 40 ppb \(O_{2}\) equivalent impurities). As noted previously in Section 2.6, the general requirements and designs for LAr provision, purification and circulation at ProtoDUNE-DP have been developed in collaboration with the larger single-phase experiments, and some of the systems are shared with ProtoDUNE-SP located nearby. Given the 20 ms lifetimes consistently achieved by ProtoDUNE-SP during its operation, it can be expected that ProtoDUNE-DP can and will reach, and likely exceed, its anticipated purity level. Like its cathode, the 6 \(\times\) 6 m ProtoDUNE-DP CRP is divided into 4 3 \(\times\) 3 m units [82]. Each of these units is constructed using an identical design to the WA105 CRP described previously: an extraction grid of wires orientated in the \(x\) and \(y\) directions and covering the entire 3 \(\times\) 3 m area of each unit, a LEM positioned 10 mm above the extraction grid and consisting of 50 \(\times\) 50 cm sub-units (36 per CRP unit), and the anode plane-separated by 2 mm from the LEM and also comprised of 36 50 \(\times\) 50 cm sub-units. The LEM units use the same physical characteristics as on WA105: 1 mm thickness, perforated by 500 um diameter holes with 800 um pitch, each with a 40 um dielectric rim. The surface design of the anode plane units, shown in Figure 46, is also identical to that of WA105. The same extraction and amplification fields (2 and 30 kV/cm respectively) are therefore also anticipated.