# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 3 Dual-Phase Experiments
### WA105 and ProtoDUNE-DP
In order to preserve the stability and flatness of each CRP unit across its entire surface, the LEM and anode plane units are mounted into a G10 fiberglass frame that spans the entire 3 \(\times\) 3 m area, which is itself then suspended from an invar (iron-nickel alloy) frame [82]. Figure 40.0 The 6 m long ProtoDUNE-DP HV extender, consisting of an inner conducting core that brings the \(-300\) kV bias from the HV feedthrough to the cathode, surrounded by an insulator. Voltage degrader rings are positioned around the insulator and connected to the nearby field cage elements in order to reduce any electric field in this region to zero. The dual-phase DUNE far detector will use a 12 m long slender of a similar design. Taken from [82]. This material is notable for its very low coefficient of thermal expansion [74]-meaning that it will undergo only a small contraction under cryogenic temperatures, and therefore that the overall deformation of the CRP as a whole will be minimised. The G10 frame is not directly attached to the invar frame in order to allow it to slide freely under its own thermal contraction without warping. The same CRP designs and components are anticipated to be used by DUNE-DP, but at a much larger scale: the 60 \(\times\) 12 m CRP will require 80 of the 3 \(\times\) 3 m units, and therefore 2880 50 \(\times\) 50 cm LEM and anode plane units [74]. Figure 47 shows the installation of the final ProtoDUNE-DP CRP unit onto the TPC. As in WA105, each CRP unit's relative flatness and height is set via three adjustable cables passing into the TPC through dedicated feedthroughs. Readout is also performed using an identical electronics system to that of WA105: the anodes are connected to PCBs sealing the lower ends of the signal feedthroughs, the front-end electronics are housed within the vacuum-tight feedthrough chimneys, and the amplified and multiplexed signals are passed to warm electronics and the final acquisition and data storage systems located outside the cryostat [82]. Following from their proven operation on WA105, the ProtoDUNE-DP PDS consists of 36 8-inch diameter Hamamatsu R5912-MOD PMTs directly coated with TPB [84]. These are located below the cathode, mounted within individual support structures that are glued directly to the interior surface of the cryostat-as shown in Figure 40.1 A stainless steel grid is positioned above the PMTs to act as a grounding plane, ensuring that there are no induced signals on the PMTs due to electrical cross-talk from the cathode. Detailed baseline and performance characterisations have been made on the PMTs prior to installation in the detector [84]. As with other detector systems, this PDS scheme will be scaled up for use on DUNE-DP, with 720 PMTs expected to be used (assuming that DUNE-DP implements the same PMT \"density\" of 1 per m\({}^{2}\) of active area as in ProtoDUNE-DP) [74]. Figure 40.2 Fine detail of the ProtoDUNE-DP anode plane surface. This design is optimised to give unambiguous 2D position reconstruction and equal charge sharing between the \(x\) and \(y\) views. An identical design has been used by WA105, and will also be used for the dual-phase DUNE far detector anode planes. Taken from [82]. Figure 40.3 Installation of the last of the four CRP units into the ProtoDUNE-DP TPC. Connection of the readouts to the corresponding signal feedthroughs was performed in-situ as each CRP unit was moved into its final position. Taken from [82]. Figure 40.4 **(Left)** One of the 36 8-inch diameter Hamamatsu R5912-MOD PMTs making up the ProtoDUNE-DP PDS, mounted in its own individual support structure that is glued directly to the interior surface of the detector cryostat. **(Right)** A view of the bottom of the cryostat, showing several of the PMTs installed. In both images, temporary plates are mounted above the PMTs for protection during installation. Both taken from [82]. Construction of ProtoDUNE-DP was completed in mid-2019, and this was followed by filling of the detector with LAr [82].