Background
The objective of this project was to investigate the tolerance of plasma detectors—specifically Channel Electron Multipliers (CEMs) and Micro-Channel Plates (MCPs)—to contamination in a dusty lunar-like environment. The research directly supported SwRI-led proposals to NASA’s recent lunar Announcements of Opportunity (AOs), which require proposers to demonstrate robust operation in the harsh, dust-laden environment of the Moon’s surface.
Approach
Two complementary test facilities were employed. For MCPs, we used SwRI’s existing MCP performance characterization system, enabling measurements of gain, resistance, uniformity, and background under dust exposure. For CEMs, we assembled a dedicated vacuum chamber facility equipped with a UV source to trigger detectors and supporting electronics to measure pulse height distributions.
Dust simulants were procured to mimic lunar regolith. The primary simulant was the Lunar South Pole high-fidelity simulant (LSP-2), representative of the Artemis-relevant landing sites. Additional tests were performed with LMS-1D simulant to better match MCP pore sizes. Detectors were gradually contaminated by manually transferring controlled amounts of simulant, followed by measurements of detector performance after each contamination step. Both mechanical deposition and limited electrostatic conditions were explored.
Accomplishments
Contrary to expectations, CEMs and MCPs demonstrated a surprising resilience to dust exposure:
- MCP Campaign #1 (LSP-2): Even after repeated contamination rounds, MCPs showed no measurable degradation in gain or background performance.
- MCP Campaign #2 (LMS-1D): Smaller-grain dust penetrated pores more effectively. Hotspots and localized gain losses were observed, especially when clumps of grains accumulated on detector surfaces. These effects were detectable in gain maps but did not result in catastrophic performance loss.
CEM Campaign: CEM detectors maintained nominal performance after initial contamination attempts, as most dust did not adhere strongly to the detector entrance.
The experiments suggest that dust may pose less of a critical vulnerability to plasma detector operation than commonly assumed, although localized effects (e.g., pore clogging) can occur under certain grain-size conditions. The research challenges assumptions about the extreme vulnerability of CEMs and MCPs to lunar dust. While localized effects were observed, detectors generally performed well even under deliberate contamination. These findings will be prepared for publication to inform the broader space science community.