# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### MicroBooNE  
In a similar vein to ICARUS T600, the Micro Booster Neutrino Experiment (MicroBooNE) detector is another previously independent single-phase LArTPC that has now been re-purposed as part of the SBN Program. Originally designed and built primarily to investigate the anomalous excess of electron-like events observed in a low energy neutrino beam by its predecessor MiniBooNE [27], MicroBooNE has operated on the Booster Neutrino Beamline at Fermilab since 2015 [12]-independently until 2018, and since then falling under the umbrella of the SBN Program, within which it is positioned as the intermediate detector [20]. The design of MicroBooNE, shown in Figures 7 and 8, is similar to that of the individual ICARUS T600 drift volumes. The 86 tonnes of active LAr are contained in a single 2.325 \(\times\) 2.560 \(\times\) 10.368 m TPC [12], which is itself enclosed by a single-walled cylindrical cryostat. A 41 cm thick layer of foam insulation covers the outside of the cryostat, acting to reduce heat input from the detector's surroundings and ensure that the interior remains at cryogenic temperature. Plastic scintillator-based cosmic ray tagger planes are positioned outside the cryostat, parallel to the four long sides of the active volume [28]. Figure 7: The MicroBooNE Liquid Argon Time Projection Chamber (LArTPC) within the cylindrical cryostat, with the row of signal feedthrough chimneys and various other access ports also shown. Taken from [12]. A view of the interior of the MicroBooNE TPC is shown in Figure 9. The cathode is made up of nine separate stainless steel panels, fixed to a supporting frame, and the bias is provided by a HV feedthrough of similar design to that used by ICARUS T600 [12]. The drift volume is physically defined by 64 field cage loops, with 4 cm centre-to-centre spacing and connected to each other using a resistor chain to generate the drift field. To achieve the purity required for a 2.5 m electron drift distance, a dedicated LAr cryogenics and purification system operates in conjunction with the main MicroBooNE detector. This system--which is extensively described in [12]--has been shown to reduce the levels of O\({}_{2}\) and H\({}_{2}\)O contamination in the active LAr volume to the order of 100 ppt following a three-stage, multi-week purging, cooling and filling process. Similarly to ICARUS T600, MicroBooNE utilises an APA consisting of three parallel wire planes for charge readout [12], with the two inner planes closest to the cathode operated in induction mode (with 2400 wires each) and the outermost one acting as a collection plane (with 3456 wires). The planes are spaced apart by 3 mm, as are the individual wires, and the induction wires are orientated at +60\({}^{\circ}\) (innermost plane) and \(-60^{\circ}\) (middle plane) to the vertical. The wires on the collection plane are orientated vertically. A close-up view of the wire planes is shown in Figure 10. During standard operation of the detector, the planes are biased at \(-200\), 0 and +440 V (innermost to outermost), which--along with the nominal cathode bias of \(-128\) kV [12]--gives a drift field of 500 V/cm and a maximum drift time of 1.6 ms.  
Figure 8: A cross-section schematic depiction of the MicroBooNE detector, with some key components labelled. Additionally depicted is the coordinate system used by the experiment (the \(z\) axis is directed towards the reader). Taken from [12]. Figure 10: A close-up view of the wire planes used in the MicroBooNE LArTPC. The plane labelling is as follows: “U” denotes the innermost (induction) plane, “V” is the middle plane (also induction), and “Y” is the collection plane. Taken from [29]. Figure 9: An interior view of the MicroBooNE TPC, showing the cathode (left), the field cage loops (centre) and the support structure for the wire planes (right). Note that the cathode panels are highly reflective due to being polished for flatness. Taken from [12].