Accelerating the development of fusion energy requires large scale simulations on cutting edge supercomputing resources.
Great hardware is only half the challenge and the software must be scalable to match.
This talk presents an objective approach to selecting a suitable back end to fusion simulations.
The UKAEA's mission is to develop commercially viable fusion energy.
Current fusion technology is yet to break even
on power out compared to power in,
thus designs for future reactors,
which necessarily must exceed break even,
carry a great amount of uncertainty.
With cost estimates of a first of a kind fusion reactor
in the order of billions of euros,
any design flaw making it through to the construction stage
will be an expensive mistake.
Thankfully, software can help.
By simulating a fusion reactor prior to construction,
the design can be tested and refined for a considerably lower cost.
However, covering all the necessary scales and physics
for a digital twin of a fusion reactor
requires computational resources at the exascale.
In this work, a number of potential finite element backends
for a multiphysics reactor simulation are evaluated.
The sheer scale makes open source a practical necessity
and scalability is the primary performance metric.
From the plethora of open source finite element libraries,
the most promising are selected
and compared against a number of objective, unbiased criteria.
None of the tested back ends scored perfectly in all criteria,
so a method and rationale for weighting the results
to select the best one for the purpose is presented.
The aspects of open source projects
that are important to high performance computing are highlighted.