Development & Characterization of Electrodes for large-scale Xenon Time Projection Chambers

TL;DR

The paper reports on the development and characterization of large-scale electrodes for xenon dual-phase TPCs, focusing on two designs: parallel-wire anodes and hexagonal-mesh cathodes, each ~1.5 m in diameter. It combines mechanical design, material testing, assembly procedures, ML-assisted defect detection, and dedicated HV tests in gaseous argon to validate performance and reliability. The HV results show robust mesh performance with a 95% survival bulk field of 3.1 kV/cm in GAr, extrapolated to LXe as at least 5.9 kV/cm, and demonstrated successful installation and operation in XENONnT upgrades. Collectively, the work provides scalable fabrication, inspection, and testing workflows for next-generation multi-ton LXe TPCs and informs design choices for XLZD-scale detectors.

Abstract

Dual-phase liquid xenon time projection chambers are the core detector elements of many experiments that conduct searches for Dark Matter and rare events, as well as in neutrino and high-energy physics. As part of this detector technology, high-voltage electrodes are instrumental for the generation of observable signals and their physical interpretation. Thus, electrode design and manufacturing has to fulfill stringent requirements, and their production is associated with significant engineering challenges. In this work we describe the successful development of electrodes on the 1.5 m-scale, from their design and simulation to subsequent assembly and high-voltage testing in a gaseous argon environment. The produced electrodes were recently installed as an anode and a cathode during an upgrade to the XENONnT experiment.

Figures (17)

• Figure 1: Left: Diagram of a typical TPC nt_instrumentlz_detector, showing the liquid and gaseous phases, the photo-sensors, the electrodes. In addition, the signal generation process is sketched out: An incident particle ($\chi$) scatters off Xe atoms, leading to an immediate scintillation signal (S1) and free electrons (e$^{-}$) through ionization. The free electrons drift to the gaseous phase, where they are accelerated, generating a secondary scintillation pulse (S2). Right: Typical field strength defined by the electrodes, with the amplification, extraction, and drift field regions labeled.
• Figure 2: Schematic drawing of the wire electrode frame mounted onto the tensioning system. The color on the electrode frame indicates the target tension of the wires in each section. The tensioning system underneath the frame consists of the tensioning rods that hold the ring, with a hexagonal screw (in yellow) adjusting the tension, and the load cells that measure the axial tension on the respective tensioning rod. The required tension on the tensioning rods is shown to the right of each rod. The band underneath the load cells limits the lateral load on the load cells. The stands support the entire structure, and the isolation connections allow the movement and relaxation of the ring and the tensioning rods. The inset shows a picture of the assembled electrode, where individual wires are separated by 5mm and fixed in place by copper pins.
• Figure 3: Schematic drawing (not to scale) and photos of different components of the wire test setup. The dashed line indicates the wire sample. The L-shaped aluminum beam profile is supported externally outside the cold bath, which is not indicated in the drawing. The vertical part of the setup consists of Fixation V that fixes the wire sample, a stretching screw that was rotated manually to increase the strain of the wire sample, a load cell measuring the axial tension on the wire sample, and the mechanical insulation that decouples the movement of the stretching screw and the load cell. Two types of Fixations V were used, either a copper gasket (a), or a screw fixing (b). The wire passed through the pulley to enter the horizontal part of the setup. Fixation H fixed the wire sample to the end of the horizontal part, either by two copper gaskets clamping the wire (c) or by a mock-up of the electrode frame segment where a copper pin was inserted to fix the wire in place (the copper pin fixation) (d). $L_v$ and $L_h$ represent the vertical and horizontal length of the wire, measured from the centre of the pulley.
• Figure 4: Results from the tensile tests at various temperatures. The top plot shows the yield strength at 0.01% offset, meaning the wire undergoes 0.01% additional deformation beyond the elastic range. The bottom plot shows the ultimate tensile strength of the sample. The right axes on both plots indicate the conversion to force acting on a wire with 0.216 mm diameter as the CFW sample. The colors indicate the wire samples. The different markers represent the different test configurations. Circles: tests with the copper gasket fixation (\ref{['fig:wire_test_setup']}(c)). Inverted-triangles: tests with the copper pin fixation, where the wire was bent by 90$^{\circ}$ (\ref{['fig:wire_test_setup']}(d)). Stars: tests with the copper pin fixation and underwent 1 thermal cycle. Dash-dotted line: the expected maximum stress on the longest wire, including the stress due to tensioning and thermal shrinkage when cooling down the TPC. The temperature gradient was assumed to be 25K based on internal communication. Dashed lines: the UTS values from the data sheet, as shown in \ref{['tab:wire_can']}.
• Figure 5: Top panel: Wire tension and resulting expected wire sagging across all wire IDs before (black) and after dismounting (blue) of the tensioning rods. The wire ID notation is defined in \ref{['fig:tensioning']}. The red dashed lines indicate the target tension of the wires. Bottom panel: Wire tension over time of selected wires. The vertical dashed line indicates the time when the tensioning rods were dismounted.