# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### Vertical Drift  
Although existing (Proto)DUNE-SP technologies, manufacturing and assembly procedures have proved to be extremely successful and will serve the neutrino sector well for many years to come, new ideas for the design of large-scale LArTPCs continue to be proposed and developed. One very recent avenue of research is known as \"Vertical Drift\" [61]--hereafter referred to as \"VD\" for convenience, and shown in Figure 35 as envisioned for a DUNE far detector module. Taking a number of cues from the design of dual-phase detectors (discussed in more detail in Section 3), the VD concept represents a shift from the established layout of single-phase LArTPCs, utilising vertical rather than horizontal electron drift. However, experience with the design and construction of ProtoDUNE-DP has shown that a vertically orientated layout is generally more efficient in terms of active LAr volume usage, due to having only one or two drift volumes, and therefore fewer components and smaller uninstrumented regions in comparison to the multiple volumes present in the larger horizontally orientated single-phase detectors. This makes such vertically orientated experiments easier to assemble [61], thus reducing required costs and time. Further reductions can also be achieved by making use of the many years of research and development that have already been performed for the (Proto)DUNE experiments-i.e., by reusing common designs, components and technologies that have already been proven and characterised. A DUNE far detector utilising the VD design will consist of two drift volumes positioned one on top of the other, with a combined active LAr mass of 14,740 tonnes and a common horizontal cathode between them. This cathode is envisioned to consist of a 58 mm thick FR4 frame with welded wire meshes covering the top and bottom surfaces [61]. The cathode bias will be provided through a HV feedthrough and extension system similar to that developed for (Proto)DUNE-DP (see Section 3.2), but due to the vertical drift length being 6.5 m, the required bias in the VD design will be 300 to 350 kV--almost twice that of the (Proto)DUNE-SP detectors, but approximately equal to that of ProtoDUNE-DP. Simi  
Figure 35: A schematic of the Vertical Drift LArTPC design, as envisioned for a DUNE far detector module. Two 6.5 m tall drift volumes are orientated vertically, with a common cathode in between, and charge readout planes (CRPs, in the form of 160 perforated PCB anodes) are positioned above and below the top and bottom drift volumes respectively. ARAPUCA photon detectors will be embedded within the cathode for direct observation of scintillation light. Taken with permission from [61]. larly, the field cage elements in the VD design are also envisioned to be the same as those on SBND, (Proto)DUNE-SP and (Proto)DUNE-DP. Recent advances in the design and manufacturing of large-area THGEMs (\"Thick Gaseous Electron Multipliers\"--a type of micropattern detector that is widely used as the anode in dual-phase TPCs, and discussed in more detail in Section 3) have allowed for the development of a new type of anode plane that has been proposed for use on a future VD detector: a perforated PCB anode [62]. This type of device, shown in Figure 36 (left), is constructed from a two-layer PCB of 3.2 mm thickness and perforated with 2.5 mm diameter holes, with each layer cut into strips of 5.2 mm width along either the \(x\) or \(y\) axis. The layers are electrically biased such that one acts as an induction plane, and the other as a collection plane. The PCB then operates in a completely analogous way to a 2-plane wire-based APA: electrons drifting towards it are focused into the holes, inducing bipolar signals on the nearby induction plane strips, and are then captured by the collection plane, creating a unipolar signal on a particular collection strip.