Presentazioni e Articoli Tecnici

Particle physics increasingly lives at the edge of what a detector can see, and novel detector concepts that harness localised, enhanced electric fields offer one way to push that edge further out - provided the underlying geometry, electric field, and ionisation transport are understood in enough detail, a task suited to detailed COMSOL Multiphysics simulation. Coherent elastic neutrino-nucleus scattering (CEvNS) offers a striking case in point: the nuclear recoil it produces in liquid argon can leave behind as few as a few tens of ionisation electrons - a signal so faint it often sits inside, not merely near, the detector's own noise floor. Recovering this reach, which offers precision access to electroweak parameters and to neutrino electromagnetic and non-standard properties, depends on rescuing exactly these smallest, most easily lost recoils.

The Liquid Argon Charge Amplification Devices (LArCADe) project approaches this problem geometrically: rather than enlarging the detector, we reshape the field around the signal itself. Nanofabricated doped-silicon tips immersed in liquid argon concentrate drifting electrons into a sharply curved, high-field apex, where curvature-driven field enhancement can turn a nearly invisible ionisation deposit into an amplified, spatially resolved signal.

We present a fabrication-informed COMSOL Multiphysics® model of this process, built directly from device geometry and governing electrostatics rather than adapted from an Application Library example. Three-dimensional tip structures are constructed from the crystallographic constraints of anisotropically etched ⟨100⟩ silicon, incorporating KOH-defined {111} facets, finite apex curvature, realistic array pitch, and the surrounding liquid-argon electrode environment. The Electrostatics interface resolves the magnitude, topology, and spatial extent of the enhanced field as a function of tip height, apex radius, spacing, and applied bias. The Charged Particle Tracing Module then follows drifting electrons into this field, characterising collection basins, focusing efficiency, and the preservation of spatial localisation.

COMSOL supplies the deterministic, macroscopic structure of field enhancement and charge collection; the microscopic liquid response is captured separately by TRANSLATE, our custom, cross-section-driven time-domain Monte Carlo framework for electron transport in argon. TRANSLATE propagates individual electrons through the COMSOL-derived, position-dependent fields, sampling momentum and energy transfer, excitation, and ionisation interactions. Coupling the two frameworks turns geometric field enhancement into physically grounded predictions of trajectories, high-field path lengths, secondary-ionisation probability, and charge-gain distributions, since frequent scattering makes peak field alone an incomplete predictor of gain in liquid argon. The resulting parameter space identifies manufacturable geometries and operating conditions that optimise gain, collection efficiency, and localisation. Prototype doped-silicon arrays are being fabricated by lithography and anisotropic wet etching at the UC Santa Barbara Nanofabrication Facility; SEM measurements will provide as-built geometries for direct simulation-to-hardware comparison ahead of cryogenic validation.

By following the signal continuously - from nuclear recoil, to drifting electron, to silicon apex, to multiplication - this work translates a rare-event neutrino problem into the language of semiconductor fabrication, electrostatic design, and microscopic charge transport: a predictive route toward lower-threshold liquid-argon detectors for CEvNS and other rare processes.