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Time-domain anode-decoupling co-design for a floating MCP TOF-MS readout

Robin F. Bonny, Lorenzo Obersnel, Martin Rubin, André Galli, Peter Wurz, Rico G. Fausch

TL;DR

This work tackles the challenge of achieving high mass-resolution TOF-MS measurements in compact, spaceborne instruments by co-designing a floating-anode MCP detector with an anode-proximal AC-decoupling network. By modeling the signal path as a combination of a low-pass anode and a high-pass decoupling stage, and validating through full-wave simulations, S-parameter measurements, circuit-level transient models, and end-to-end MS tests, the authors show that a planar circular patch anode preserves pulse fidelity while suppressing undershoot and baseline wander. The study demonstrates that the decoupling network’s high-pass corner directly governs undershoot decay and baseline recovery, enabling fast settling with minimal post-pulse energy. The resulting flight-ready, compact detector matches waveguide-based performance at a fraction of mass and volume and is being adopted in CODEX and other next-generation spaceborne TOF-MS instruments, underscoring its practical impact for planetary research and small spacecraft mass spectrometry.

Abstract

We present a microchannel plate detector for compact time-of-flight mass spectrometers (TOF-MS) that jointly optimizes the anode geometry and high-voltage AC-decoupling network for electrically floating operation. Undershoot-driven baseline artifacts and pulse broadening are addressed by a time-domain co-design of the anode geometry and decoupling network. The design is validated through a staged workflow that combines full-wave electromagnetic simulations, vector network analyzer measurements, circuit-level transient models, and end-to-end mass spectra. The resulting planar circular patch anode with anode-proximal decoupling confines fields, preserves peak amplitude, and suppresses post-pulse energy, leading to fast settling and minimal baseline wander. We show that the effective high-pass corner set by the decoupling capacitance directly governs undershoot decay and baseline recovery. Measurements in a representative TOF-MS test setup demonstrate waveguide-level pulse fidelity at a fraction of the mass and volume of heritage waveguide-based detectors, with residual ripples in the measured response originating from downstream cable and digitizer terminations rather than the detector itself. By limiting detector-induced temporal broadening and inter-peak baseline coupling, the design supports high mass resolution and dynamic range in miniaturized TOF-MS architectures. Variants of this planar flight-ready architecture are being implemented in several next-generation spaceborne TOF-MS instruments currently under development at the University of Bern.

Time-domain anode-decoupling co-design for a floating MCP TOF-MS readout

TL;DR

This work tackles the challenge of achieving high mass-resolution TOF-MS measurements in compact, spaceborne instruments by co-designing a floating-anode MCP detector with an anode-proximal AC-decoupling network. By modeling the signal path as a combination of a low-pass anode and a high-pass decoupling stage, and validating through full-wave simulations, S-parameter measurements, circuit-level transient models, and end-to-end MS tests, the authors show that a planar circular patch anode preserves pulse fidelity while suppressing undershoot and baseline wander. The study demonstrates that the decoupling network’s high-pass corner directly governs undershoot decay and baseline recovery, enabling fast settling with minimal post-pulse energy. The resulting flight-ready, compact detector matches waveguide-based performance at a fraction of mass and volume and is being adopted in CODEX and other next-generation spaceborne TOF-MS instruments, underscoring its practical impact for planetary research and small spacecraft mass spectrometry.

Abstract

We present a microchannel plate detector for compact time-of-flight mass spectrometers (TOF-MS) that jointly optimizes the anode geometry and high-voltage AC-decoupling network for electrically floating operation. Undershoot-driven baseline artifacts and pulse broadening are addressed by a time-domain co-design of the anode geometry and decoupling network. The design is validated through a staged workflow that combines full-wave electromagnetic simulations, vector network analyzer measurements, circuit-level transient models, and end-to-end mass spectra. The resulting planar circular patch anode with anode-proximal decoupling confines fields, preserves peak amplitude, and suppresses post-pulse energy, leading to fast settling and minimal baseline wander. We show that the effective high-pass corner set by the decoupling capacitance directly governs undershoot decay and baseline recovery. Measurements in a representative TOF-MS test setup demonstrate waveguide-level pulse fidelity at a fraction of the mass and volume of heritage waveguide-based detectors, with residual ripples in the measured response originating from downstream cable and digitizer terminations rather than the detector itself. By limiting detector-induced temporal broadening and inter-peak baseline coupling, the design supports high mass resolution and dynamic range in miniaturized TOF-MS architectures. Variants of this planar flight-ready architecture are being implemented in several next-generation spaceborne TOF-MS instruments currently under development at the University of Bern.
Paper Structure (28 sections, 16 equations, 10 figures, 3 tables)

This paper contains 28 sections, 16 equations, 10 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Time-of-flight mass spectrometry
  3. Detection limitations
  4. Detector architecture
  5. Reference designs and data
  6. Methods
  7. Signal-path abstraction
  8. Anode: Low-pass limit
  9. Decoupling: High-pass limit
  10. Development workflow
  11. Full-wave simulation
  12. Electrical performance
  13. Circuit-level transient model
  14. End-to-end mass spectra
  15. Metrics and processing
  16. ...and 13 more sections

Figures (10)

  • Figure 1: Schematic MCP detector overview: floating anode with proximal AC-decoupling feeding a 50 readout.
  • Figure 2: Readout circuit lumped-element schematic divided into high-voltage (HV) and low-voltage (LV) sections.
  • Figure 3: Encased NIM prototype detector with visible ion inlet in the center and bias/readout connectors at the bottom.
  • Figure 4: HFSS two-port spiral anode model for transient response simulation.
  • Figure 5: Simulink time-domain model with synthesized (lumped) elements to study undershoot and settling.
  • ...and 5 more figures