Dual-Phase TPC Extraction Grid Development and Production in Darkside-20k Prototypes

A number of physics collaborations around the world today employ time projection chambers (TPCs) in highly sensitive detectors to search for evidence of rare particles. The dual-phase TPC detector concept relies on two unique (but related) event signals, S1 and S2, to increase a detector's effectiveness against backgrounds. The Darkside-20k (DS-20k) experiment applies this idea to dark matter detection. In its detectors, DS-20k utilizes an S1 signal from recoil-induced photon emissions in liquid Argon, and an S2 signal from induced collisions between ionization electrons and the "second phase" gas pocket of the TPC. A uniform electric drift field is applied to the lower liquid volume to direct ejected electrons towards an extraction grid; there a second, stronger field accelerates them into the gas region. The extraction grids for the DS-20k prototypes Proto-0 and Mockup were carefully designed and constructed to ensure field uniformity and resistance to destructive forces from their detectors. A wound-pin technique was used to produce replaceable grid wire units from stainless steel which can maintain this function. The development and production of these two grids was used to inform the final design and assembly procedures for the DS-20k grid.