The DiRAC 2.5x Facility

Physicists across the astronomy, nuclear and particle physics communities are focussed
on understanding how the Universe works at a very fundamental level. The distance scales
with which they work vary by 50 orders of magnitude from the smallest distances probed
by experiments at the Large Hadron Collider, deep within the atomic
nucleus, to the largest scale galaxy clusters discovered out in space. The Science challenges,
however, are linked through questions such as: How did the Universe begin and how is it evolving?
and What are the fundamental constituents and fabric of the Universe and how do they interact?

Progress requires new astronomical observations and experimental data but also
new theoretical insights. Theoretical understanding comes increasingly from large-scale
computations that allow us to confront the consequences of our theories very accurately
with the data or allow us to interrogate the data in detail to extract information that has
impact on our theories. These computations test the fastest computers that we have and
push the boundaries of technology in this sector. They also provide an excellent
environment for training students in state-of-the-art techniques for code optimisation and
data mining and visualisation.

The DiRAC2 HPC facility has been operating since 2012, providing computing resources for theoretical research
in all areas of particle physics, astronomy, cosmology and nuclear physics supported by STFC. It is a highly productive
facility, generating more than 250 papers annually in international, peer-reviewed journals. However, the DiRAC2 hardware is now at least 5 years old and is therefore at significant risk of failure. The loss of any one of the DiRAC2 services
would have a potentially disastrous impact on the research communities which rely on it to deliver their scientific research. The main
purpose of the requested funding for the DiRAC2.5x project is to replace the ageing DiRAC2 hardware at Durham, Edinburgh and Leicester
while taking advantage of recent hardware advances to provide some new capabilities (e.g. i/o acceleration using flash storage) as prototypes for
the proposed DiRAC3 services.

DiRAC2.5x builds on the success of the DiRAC HPC facility and will provide the resources needed to support cutting-edge research
during 2018 in all areas of science supported by STFC. While the funding is required to "keep the lights on", the science programme will continue to be
world-leading. Examples of the projects which will benefit from this investment include:

(i) lattice quantum chromodynamics (QCD) calculations of the properties of fundamental particles from first principles;
(ii) improving the potential of experiments at CERN's Large Hadron Collider for discovery of new physics by increasing the accuracy of theoretical predictions for rare processes involving the fundamental constituents of matter known as quarks;
(iii) simulations of the merger of pairs of black holes which generate gravitational waves such as those recently discovered by the LIGO consortium;
(iv) the most realistic simulations to date of the formation and evolution of galaxies in the Universe;
(v) the accretion of gas onto supermassive black holes, the most efficient means of extracting energy from matter and the engine which drives galaxy formation and evolution;
(vi) new models of our own Milky Way galaxy calibrated using new data from the European Space Agency's GAIA satellite;
(vii) detailed simulations of the interior of the sun and of planetary interiors;
(viii) the formation of stars in clusters - for the first time it will be possible to follow the formation of stars many times more massive than the sun.

The anticipated impact of the DiRAC2.5x HPC facility aligns closely with the recently published UK Industrial Strategy. As such, many of our key impacts will be driven by
our engagements with industry. Each service provider for DiRAC2.5x has a local industrial strategy to deliver increased levels of industrial returns over the next three years.
The "Pathways to impact" document which is attached to this proposal describes the overall industrial strategy for DiRAC2.5x, including our strategic goals and key performance indicators.