Tech Briefs Magazine - October 2023 - Comsol-22A

SIMULATION-BASED PRODUCT DEVELOPMENT
FIGURE 5 Ray tracing models
showing the simulated paths of
electrons (blue) and ions (red) in the
IE514.
gauge. INFICON and two other project
participants, NOVA University Lisbon
and the European research lab CERN,
each developed simulation models of the
IE514 design. The results generated by
each model were compared to test results
from a physical prototype of the IE514
gauge to ensure the models' accuracy
before proceeding with new designs.
Francesco Scuderi, an INFICON
engineer, used the COMSOL Multiphysics®
software to model the IE514 (Figure
3). The model enabled analysis of
thermionic electron emissions from the
filament and the ionization of gas by
those electrons. The model can also
be used for ray tracing the paths of
generated ions toward the collector. With
these simulated outputs, Scuderi could
calculate an expected sensitivity factor,
which is based on how many ions are
detected per emitted electron - a useful
metric for comparing the overall fidelity
of the model with actual test results.
" After constructing the model
geometry and mesh, we set boundary
conditions for our simulation, " Scuderi
explains. " We are looking to express
the coupled relationship of electron
emissions and filament temperature,
which will vary from approximately
1400 to 2000°C across the length of the
filament. This variation thermionically
22a COMSOL NEWS
affects the distribution of electrons and
the paths they will follow. " (Figure 4)
" Once we simulate thermal conditions
and the electric field, we can begin
our ray tracing simulation, " Scuderi
continues. " The software enables us
to trace the flow of electrons to the
grid and the resulting coupled heating
effects. " Next, the model is used to
calculate the percentage of electrons that
collide with gas particles. From there,
ray tracing of the resulting ions can be
performed, tracing their paths toward
the collector (Figure 5).
" We can then compare the quantity
of circulating electrons with the number
of ions and their positions. From this, we
can extrapolate a value for ion current
in the collector and then compute the
sensitivity factor, " says Scuderi.
INFICON's model simulated values that
closely aligned with test results from
the benchmark prototype. This enabled
the team to observe how changes to the
modeled design affected key metrics,
including ionization energy, the paths
of electrons and ions, emission and
transmission current, and sensitivity.
M » SIMULATION LED TO A
ORE ROBUST GAUGE
The end product of INFICON's design
process, the IRG080, incorporates many
of the same components as existing
Bayard-Alpert gauges, but key parts look
quite different. For example, the new
design's filament is a solid suspended disc,
not a thin wire. The grid is no longer a
delicate wire cage but is instead made
from stronger formed metal parts. The
collector now consists of two components:
a single pin or rod that attracts ions and a
solid metal ring that actually helps direct
electron flow away from the collector and
toward a Faraday cup. This arrangement,
refined through ray tracing simulation
with the COMSOL Multiphysics software,
improves accuracy by better separating
the paths of ions and electrons.
Testing showed that the IRG080
achieved the goal of reducing
measurement uncertainty to below
1%. In regard to sensitivity, the IRG080
performed eight times better than the
benchmark. Just as importantly, the
INFICON prototype yielded consistent
results during multiple testing sessions,
delivering sensitivity repeatability
performance that was 13 times better
FIGURE 6 The COMSOL model of
the IRG080 gauge.
than that of the benchmark gauge.
Twenty-three identical gauges were
built and tested during the project,
confirming that INFICON had created a
more precise, robust, and reproducible
tool for measuring HV/UHV conditions.
At the completion of the ion gauge
project, the INFICON team hoisted
an impressive trophy: the IRG080
itself. Of course, this success was not
the team's alone. INFICON benefited
from its partners' support; in turn, the
broader scientific and manufacturing
community will benefit from more
consistent measurements of HV/UHV
conditions.
ACKNOWLEDGEMENTS
Participants of the EMPIR ionization
gauge project include PhysikalischTechnische
Bundesanstalt, Cesky
Metrologicky Institut Brno, Institut
za Kovinske Materiale in Tehnologije,
Laboratoire national de métrologie
et d'essais, RISE Research Institutes of
Sweden AB, European Organization for
Nuclear Research, Faculdade de Ciências
e Tecnologia Universidade Nova de
Lisboa, VACOM Vakuum Komponenten
& Messtechnik GmbH, and INFICON
Aktiengesellschaft.
Tech Briefs Magazine - October 2023

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