Anna Gura
Research Project
My research dealt with conducting simulations of
electrons in a velocity map imaging spectrometer. Using SIMION, an ion
and electron optics simulator, I was able to model the path that
electrons would take through an applied electric field. For these
simulations I was able make technical modifications to the set-up,
adjust the electric field, vary the electron energies, and ultimately
characterize the spectrometer.
Goal
The standard velocity map imaging (VMI) model
consists of a simple design of three electrodes (a repeller, extractor
and a ground electrode) and a detector. An electrostatic lens that
projects electrons onto the imaging detector can be formed with the
application of appropriate voltages to the first two electrodes (the
repeller and the extractor). The detector lies at a relatively long
distance away from the three electrodes, a distance that is necessary in
order to achieve high resolution. This detector is capable of measuring
charged particles. However, because the detector is relatively far away
from the electrodes, limits are imposed on the highest possible energies
that can be detected. Typically, the standard VMI can measure electrons
up to about 100 eV.
In recent years a new VMI has been designed and
implemented in the JRM lab. This design consists of many more electrodes
and can potentially measure electrons with three-times the energy of
highest measurable energies of the standard VMI (around 300 eV), with
better resolution. Already
the design has been copied in Florida, Korea, and Australia.
The goal of this project was to characterize, through SIMION simulations, the high-energy VMI, including finding the best possible set of voltages for the electrodes which produces the highest resolution for a range of electron energies. The results from these simulations were then compared to data from the standard VMI and experimental results.
Using these simulations and comparisons to the standard VMI model and experimental results, we see that the high energy VMI allows for the use of higher-energy electrons and produces better resolution.
Results and Interpretation
We investigated several cases of voltage meant to be set on the repeller
electrode in the high-energy VMI. For reasons of practicality and
availability, the main focus was when the repeller was set to -10kV.
The first challenge was finding the best set of voltages for the rest of
the electrodes. The purpose of finding this was to create an
electrostatic lens which would send the electrons in such a path that
would result in the group of electrons being focused at the detector.
Once we found the desirable set of voltages and the electron energies
that worked well in that electric field, we had enough data to compare
our results to those of the standard VMI design.
Using these simulations and comparisons of the high-energy VMI to the
standard VMI model and experimental results, we see that the high energy
VMI allows for the use of higher-energy electrons and produces better
resolution.
For a more detailed description of the project and our findings, please see my final report which can be found on this website.
