A low-cost computer cluster for the calculation of atomic data of importance in plasma physics

High resolution spectroscopy is of major importance in many areas of plasma physics, and provides information on a diverse range of laboratory and astrophysical plasmas, including e.g. magnetically-confined tokamaks, laser-produced plasmas and the solar corona. A vital requirement for the modelling of high resolution spectra is accurate data for a range of atomic physics parameters and processes, including e.g. energy levels, transition probabilities and electron impact excitation cross sections. At Queen's University Belfast (QUB), we have a highly productive research programme on the calculation of atomic data for applications in plasma physics, using our sophisticated codes such as RMATRX. Our calculations have been undertaken primarily on a cluster of 18 personal computers (PCs), purchased in 2005 via an EPSRC equipment grant. However, the cluster is now out of warranty, with several machines no longer operational. Just as importantly, the workstations now provide, by current standards, poor processing power, due to the rapid advances in CPU processor technology and speed. As a consequence, the productivity and competitiveness of our atomic physics research programmes are being seriously affected. In this proposal we therefore seek modest funding for the purchase of 7 new PCs. This funding will be matched by the School of Mathematics and Physics at QUB, so that a total of 14 PCs can be purchased, providing a cluster which will have a computational power more than an order of magnitude greater than our existing cluster.The new PC cluster will be employed to produce highly accurate atomic data in support of a number of major experimental spectroscopic programmes, in particular those involving tokamaks. These are magnetically-confined plasma devices which have been built for the study and eventual generation of nuclear fusion. In the UK, tokamak experiments are undertaken at the Culham Centre for Fusion Energy. This is the site of several tokamaks, including the Joint European Torus (JET), the world's largest. We will undertake atomic physics calculations to help model new and innovative JET experiments, which will address several key issues in plasma science, including (i) assessing the efficiency of impurity ion extraction using the divertor on JET, (ii) diagnosing the alpha-particle yield during fusion.We will also undertake atomic physics calculations for input to the GALAXY and CLOUDY codes, widely used in the UK to model photoionisation-dominated laboratory and astrophysical plasmas, respectively. The predictions from the codes will be compared with an X-ray spectrum of a well-diagnosed photoionisation-dominated silicon plasma generated using the GEKKO-XII laser facility. This in turn will allow us to benchmark the CLOUDY code under physical conditions similar to those found in photoionisation-dominated astronomical sources, in particular active galactic nuclei (including quasars). We will also be able to benchmark the laboratory code GALAXY under extreme photoionisation conditions.

We plan to undertake atomic physics calculations in support of tokamak experimental programmes at the Culham Centre for Fusion Energy. Tokamaks are magnetically-confined plasma devices that have been built for the study (and eventual generation) of nuclear fusion. Research on tokamaks is a multi-billion dollar worldwide industry, due to the possibility of developing a commercial nuclear fusion energy source via these devices. Steady-state fusion and commercial energy generation are still a long way off, and numerous problems remain to be overcome. It is clear that many years of research will be required on these problems, which include e.g. energy loss in the tokamak, the efficiency of heating mechanisms, and the rate and yield of nuclear fusion reactions. However, when these are overcome the benefits will be enormous, as such an energy source will be abundant, relatively cheap, and (perhaps most importantly) environmentally friendly. Hence the impact on society of commercial energy generation via tokamaks will clearly be enormous. To maximise the impact of our atomic physics calculations on the international tokamak community, the data will be incorporated into the Atomic Data and Analysis Structure (ADAS) packages, which are employed in the analysis of the spectra from the tokamaks at Culham. However, through their inclusion in ADAS, our results will also be used by other ADAS participants working on tokamak spectral observations, such as ASDEX at the Max-Planck-Institut fur Plasmaphysik in Garching (Germany), and Tore Supra Association EURATOM-CEA sur la Fusion in Cadarache (France). In addition, several major groups which are not part of the ADAS community will have access to our results via their strong collaborative links with Culham, such as the TFTR at Princeton (USA) and the JT-60U at the Japan Atomic Energy Research Institute in Naka-machi (Japan). We also plan to undertake atomic physics calculations in support of experimental programmes to benchmark plasma modelling codes such as GALAXY (laboratory code) and CLOUDY (astrophysical code) in the photoionisation-dominated regime. The benchmarking of laboratory codes such as GALAXY is of major interest to AWE Aldermaston, as it is of relevance to their laser-produced plasma experiments and modelling. The PI has very close links with AWE, which includes the funding of his William Penney Fellowship. As a consequence, he is well placed to communicate the results of the work to AWE and hence maximise its impact on their research programmes. Research related to astrophysical modelling codes such as CLOUDY has limited direct impact outside the academic sector. On the other hand, astronomy is undoubtedly the most popular area of physics with schoolchildren and the general public. It can help to enthuse children about physics (and science in general), and encourage them to study the subject at school and university. Hence the societal impact of astronomy is very high indeed, in terms of the Public Understanding of Science (PUS). The PI and his colleagues within the Astrophysics Research Centre in the School of Mathematics and Physics at Queen's University Belfast are highly active in outreach programmes linked to their research. We intend to incorporate our work - which can be publicised to an audience as `Creating an active galaxy or quasar in the laboratory' - into our PUS talks and presentations.