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ITACA revisited: Ion Tracking Apparatus with CMOS ASICs

J. J Gómez-Cadenas, L. Arazi, G. Martínez-Lema, J. Renner, S. R. Soleti, S. Torelli

Abstract

High-pressure xenon gas TPCs with electroluminescent amplification (HPXeEL) provide detailed topological reconstruction of charged-particle trajectories, offering a distinctive two-electron signature for neutrinoless double beta decay ($0ββν$) searches. We have recently proposed ITACA, a detector concept that images both the electron track and the corresponding ion track, carried by the positive ions drifting in the opposite direction. While electrons drift rapidly to the anode for standard EL imaging, the positive ions drift slowly to the cathode with millimetre-scale diffusion, allowing time to determine the event energy and barycenter and to position a movable ion detector at the projected arrival point of the ion cloud. We present a conceptual design of the ITACA detector, addressing key feasibility questions. First, we define the detector geometry and operating parameters for a 1-tonne-scale instrument at 15 bar, including a modular tiled electroluminescent structure. Second, we present the conceptual design of the Magnetically Actuated Rotor System (MARS), the mechanism that positions the ion sensor at any $(r, θ)$ coordinate below the cathode, and show that the expected movement time is fast enough to retain $\sim95\%$ of the drift volume for ion detection, while not significantly perturbing the gas on the scales of the ion drift. Third, we propose using a Topmetal CMOS ASIC-based ion detector as an alternative to the molecular sensor approach described in our original work, enabling real-time, 3D imaging of the ion track without the need for offline laser scanning. Finally, we estimate the sensitivity of the proposed apparatus, showing that enhanced topological discrimination from the ion track, combined with an ultra-low background design, allows exploration of $0ββν$ half-lives in excess of $10^{28}$ yr.

ITACA revisited: Ion Tracking Apparatus with CMOS ASICs

Abstract

High-pressure xenon gas TPCs with electroluminescent amplification (HPXeEL) provide detailed topological reconstruction of charged-particle trajectories, offering a distinctive two-electron signature for neutrinoless double beta decay () searches. We have recently proposed ITACA, a detector concept that images both the electron track and the corresponding ion track, carried by the positive ions drifting in the opposite direction. While electrons drift rapidly to the anode for standard EL imaging, the positive ions drift slowly to the cathode with millimetre-scale diffusion, allowing time to determine the event energy and barycenter and to position a movable ion detector at the projected arrival point of the ion cloud. We present a conceptual design of the ITACA detector, addressing key feasibility questions. First, we define the detector geometry and operating parameters for a 1-tonne-scale instrument at 15 bar, including a modular tiled electroluminescent structure. Second, we present the conceptual design of the Magnetically Actuated Rotor System (MARS), the mechanism that positions the ion sensor at any coordinate below the cathode, and show that the expected movement time is fast enough to retain of the drift volume for ion detection, while not significantly perturbing the gas on the scales of the ion drift. Third, we propose using a Topmetal CMOS ASIC-based ion detector as an alternative to the molecular sensor approach described in our original work, enabling real-time, 3D imaging of the ion track without the need for offline laser scanning. Finally, we estimate the sensitivity of the proposed apparatus, showing that enhanced topological discrimination from the ion track, combined with an ultra-low background design, allows exploration of half-lives in excess of yr.

Paper Structure

This paper contains 32 sections, 25 equations, 16 figures, 15 tables.

Table of Contents

  1. Introduction
  2. The ITACA Detector
  3. Design criteria and tradeoffs
  4. Main subsystems
  5. TPC and EL Detection System
  6. Principle of operation
  7. The MARS System
  8. Concept
  9. Geometry
  10. Xenon gas at 15bar
  11. Motion Sequence
  12. Gas Disturbance Mechanisms
  13. Boundary layer thickness.
  14. Turbulent transport after motion stops.
  15. Potential flow:
  16. ...and 17 more sections

Figures (16)

  • Figure 1: Left: transverse diffusion of ${\rm Xe_2^{+}}$ ions as a function of drift length for three different drift fields; right: transverse diffusion of ${\rm Xe_2^{+}}$ ions compared with transverse diffusion of electrons in pure xenon.
  • Figure 2: Cross-section (XZ view) of the ITACA detector showing the main subsystems. Not to scale.
  • Figure 3: Principle of operation of the ELMAS. Drift electrons are driven into the FAT-GEM by the intense electric field (about 2kV/cm/bar) following the field lines shown in the top-right panel. Inside the channels, electrons produce VUV electroluminescence. The light is subsequently wavelength-shifted into the visible range through TPB-coating of the holes' walls. Part of the light going backwards is detected by the BFD. The light exiting the FAT-GEM channels is directed towards the Light Guide Honeycomb, which transports it to the DSP.
  • Figure 4: Conceptual design of the BFD Soleti2024FiberBarrel.
  • Figure 5: XY view of the MARS system, showing the dual-arm propeller, copper rail, and ion plate positions.
  • ...and 11 more figures