XUV and X-ray Probing of Warm Dense Matter

In this research we are seeking to further investigate a very interesting form of matter called 'warm dense matter' or WDM. This is a state of matter that is expected to be found, for example, in the cores of giant planets like Jupiter and Saturn and to a lesser extent the Earth. The matter is characterized by being at high density (sometimes above normal solid density) and at an elevated temperature ranging from 10,000K to well above 1 million degrees. This means that the pressure is enormous, reaching several million times atmospheric pressure. Under these conditions the matter is not expected to behave either like a normal solid or like a classical plasma.

We will make samples of warm dense matter in a variety of ways. One of these involves using intense laser pulses to drive very strong shocks into solid samples, thus compressing and heating them. We will probe these samples with intense x-rays generated from another laser-plasma. This takes place on a timescale of less than a billionth of a second. The results will test the electronic structure of the matter under WDM conditions. In other types of experiment, we will heat solid foils with x-rays generated from laser-heated targets. This will raise the temperature of the solid matter to several thousand degrees. We will probe this matter with XUV radiation generated from gas-laser interactions using high harmonics of the initial laser wavelength. This will help to measure the degree to which XUV radiation is absorbed.

The work proposed in this project is, by its nature, academic science and thus connection to potential economic impact is less obvious at present. However, we can consider the wider impact on the general public outside of the scientific community. There is a considerable public appetite for science, especially related to fundamental questions on the nature of the universe, for example the search for the Higgs Boson, Dark Matter and the recently resolved controversy over the speed of neutrinos. There is also a wide public interest in astrophysical sciences- with a very active amateur astronomy community.

Our work on the structure of warm dense matter is very closely related to the planetary and astrophysical sciences. An understanding of warm dense matter- be it water, hydrogen, ices or heavier materials such as iron, is essential to the understanding of planetary structure and crucically their formation. There are currently hundreds of known exo-solar planets. These are mostly large planets, probably gas giants. A better understanding of planetary formation and structure may help improve estimates of the number that may be Earth-like and understanding warm dense matter is a part of this process. Thus, we believe that our work is in general closely related to science that the public has an interest in. Such public interest is in turn good for science generally. The TARANIS laser, which forms a key part of the research programme is itself a significant part of our outreach programme in that, on open days, UCAS days and other events where young people visit our department, it is a key stop-off point on the tour of the department. It has hosted young researchers on summer internships and is well integrated into our 4th year MSci undergraduate projects programme.