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By Alexander Palov, Arturo Keer, and Robin Devonshire, Cavendish Instruments
Ltd.,Sheffield, UK
Cavendish Instruments Ltd. (www.cavendishinstruments.com),
a Fluent business partner, is developing a general purpose plasma modeling
environment that is fully coupled to FLUENT 6. The plasma components are
derived from codes developed at Sheffield University to describe low and
high pressure atomic and molecular gas discharges, which are used as radiation
sources in general lighting or other more specialized applications. The
governing equations used in these codes are of a fundamental and general
nature, and when coupled to FLUENT 6, they create a powerful and novel
3D, time-dependent plasma modeling capability.
Electric potential in the U-lamp
3D grid for plasma modeling of the low-pressure discharge in the U-lamp
In the new code, the number density, momentum,
and energy equations for both electrons
and ions are implemented through user-defined
scalars (UDS) and species transport equations
are used to describe the ground and excited
states of neutral atoms. For systems where radiation
transport processes are important, the
discrete ordinates method is being used, at least
initially. The code is being validated using a plasma
system for which there is reliable modeling
data and where there is an extensive program
of experimental diagnostics in progress at Sheffield
University.
In separate work, Cavendish Instruments has
coupled FLUENT to a powerful chemical species
database called MTDATA (from the National
Physics Laboratory, Teddington, UK) to create
Ehecatl, a code that has been used very successfully
by companies and research groups to
simulate complex bulk and surface chemistry
in thermal systems such as CVD coaters and
halogen lamps. In the future, Cavendish plans
to couple Ehecatl with their new plasma code.
The plasma code is also being used in a program
to develop novel plasma - electric circuit
models to help identify optimum system configurations.
A critical issue in the simulation of any plasma system is the availability
of data for the electron-, photon- and ion–atom/molecule collision
cross-sections, transition probabilities, and volume and surface chemical
reaction rates. Cavendish Instruments is taking a very broad and long-term
approach to this issue by combining assessed published data with data
estimation methods and direct data calculation using advanced ab initio
methods (derived from the Schrödinger equation and fundamental constants),
available either in-house or via collaboration with world leading academic
groups.
A DC ultra high performance (UHP) lamp
Electric potential of an operating DC UHP lamp
The plasma code is being developed in collaboration
with several end-user companies. Other
users interested in simulating their plasma processes
are actively being sought to help expand
the scope and validation of this software.
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