Simulation of grid morphology’s effect on ion optics and the local electric field

Author:

Levin Z.1ORCID,Kempf S.1ORCID

Affiliation:

1. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA and Solar System Exploration Research Virtual Institute (SSERVI) - Institute for Modeling Plasmas, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, Colorado 80303, USA

Abstract

Electric field ion optics are employed by many scientific instruments for investigating ions, e.g., using time-of-flight mass spectrometers. A common design feature of such instruments is the grounded grid that provides boundaries between regions that need to have different electric fields. In order to save computer memory, these grids are often modeled by indefinitely thin conducting sheets. This approximation does not include the effects of the grid morphology on the electric field. This paper investigates these grid morphology effects on both the electric field and the trajectories of ions passing through the grids using finite element analysis. The simulations in this paper indicate that a significant amount of the electric potential will leak through a grid’s empty space. The leakage of this field through the grid slows an ion down relative to the speed that it would be assumed to have based on the indefinitely thin sheet model. The ions are then eventually accelerated back to the energy that they would have if the grid were a thin sheet. However, this deceleration and acceleration result in the lengthening of the ion time of flight, independent of the size of the drift region. The deflection of the ions passing through the grid increases with the ion’s proximity to the grid struts, the size of the acceleration region, and the shape of the grid cell. This deflection also results in a small but potentially significant loss of focus and changes in the path length.

Funder

National Aeronautics and Space Administration

Publisher

AIP Publishing

Subject

General Physics and Astronomy

Reference8 articles.

1. Simion 2019 supplemental documentation, “Grid” Technical Report (Scientific Instrument Services, 2019).

2. R. King III, “LASER Desorption/LASER Ionization Time-of-Flight Mass Spectrometry Instrument Design and Investigation of the Desorption and Ionization Mechanisms of Matrix-Assisted LASER Desorption/Ionization,” Drexel University, 1994.

3. Reducing grid dispersion of ions in orthogonal acceleration time-of-flight mass spectrometry: advantage of grids with rectangular repeat cells

4. Ion dispersion near parallel wire grids in orthogonal acceleration time-of-flight mass spectrometry: predicting the effect of the approach angle on resolution

5. Origin of the May 1998 suprathermal particles: Solar and Heliospheric Observatory/Charge, Element, and Isotope Analysis System/(Highly) Suprathermal Time of Flight results

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