The measurement problem

The PSPL project studied a practical measurement problem in electric-thruster ground testing. When an ion beam strikes chamber hardware or a beam target, secondary species emissions can contaminate particle-density and current measurements. The report proposed a biased electrostatic filter: a dual-layer charged grid placed near the beam target to suppress lower-energy secondary particles while letting the higher-energy incident beam pass with minimal disruption.

What was modeled

The model treated the vacuum chamber as a grounded cylindrical domain and placed charged tungsten-wire grids between the beam target and the region where secondary particles would rebound. The design variables were intentionally physical: wires per layer, layer count, parallel separation, vertical clearance, wire radius, and applied potential.

The report moved through staged simulations. Early runs validated the field shape in simple geometries. Later stages compared vertical clearance, parallel separation, voltage-sign ordering, and particle tracing behavior. The central engineering question was not whether a charged grid can create a field. It was which geometry gives useful suppression without becoming impossible to manufacture or disruptive to the test environment.

Simulation evidence

The report includes particle trajectories, electrostatic fields, parameter sweeps, and a SolidWorks model of the filter assembly.

PSPL positron beam particle trajectory traces from the biased filter report
Figure 19: positron-beam trajectory tests, with the upper comparisons around 420 eV and the lower comparison around 10 eV.
Electrostatic field visualization for the PSPL biased filter geometry
Figure 21: electrostatic field visualization after introducing a grounded plate near the filter geometry.
Vertical potential line plot comparing original and shifted plate cases
Vertical potential comparison for original, +10 cm, -10 cm, and -20 cm grounded-plate positions.
Hemispherical 10 eV electron trajectories from the beam target surface
Figure 22: 300 hemispherically released 10 eV electrons from the beam-target surface, used to test whether the filter blocks secondary species under a more realistic release model.
EMI+ cation trajectory simulation at 10 eV
Figure 23 left: EMI+ cation test at 10 eV, a heavier charged species case.
IM- anion trajectory simulation at 10 eV
Figure 23 right: IM- anion test at 10 eV, paired with the cation case to stress the charge and mass assumptions.
PSPL phase diagram for parallel separation and vertical clearance parameter sweep
Figure 25: phase diagram summarizing how parallel separation and vertical clearance affect maximum potential and practical geometry choice.
SolidWorks model of the PSPL biased filter and beam target assembly
Figure 27: SolidWorks model translating the simulation geometry into a beam-target and biased-filter assembly.

Design comparison

Biased-filter design comparison from the PSPL report.
Design choiceResultInterpretation
Alternating polarityWeak central potential in several geometries.Neighboring layers partially cancel the field where suppression is needed.
Separated polarityStronger useful potential.Grouping same-sign layers preserves a more meaningful barrier near the target.
Smaller parallel separationHigher central potential.Denser grids strengthen the local field but raise manufacturing and obstruction costs.
Larger vertical clearanceStronger potential under opposite-polarity assumptions.Geometry matters as much as voltage magnitude.

Research output

I produced the simulation study and a SolidWorks model of the filter and beam-target assembly. The figures and comparisons above are drawn from the research report; the results describe simulated performance.