Enhancement was seen on the 64.8 Å line.Įxperimental evidence in recent years has shown that our understanding of radiative opacity in high energy density environments is not complete. The technique of bootstrapping was employed that allowed several different real and null experimental shots to be combined in a statistically meaningful way and resulted in a probability distribution for the enhancement.įigure shows the KCl line-coincidence pumping scheme. The experimental analysis employed both real (KCl) and null (NaCl) shots. The experiments are relevant to astrophysical plasmas in which we have recently shown that a similar process operates. The experiments have shown a population enhancement in upper levels of H-like Cl which was diagnosed by enhancement of spectral line intensity of the n=4-3 transition in the H-like Cl ions. We have modelled experiments on the ORION laser at AWE that have shown line-coincidence photopumping of H-like Cl by H- and He-like K ions in the same plasma for the first time. A mechanism often considered is line coincidence photopumping, in which a strong, narrow-band source of X-rays produced by line radiation from one plasma is used to pump directly a resonant transition in a physically separate plasma. RoseĮxperiments have been performed over a number of years that attempt to tailor the radiation field in a laser-produced plasma and thereby influence, by direct photopumping, the excitation and ionisation. As they do so they induce large amplitude plasma waves, and their interaction with these waves leads to the modulated structures evident in the figure.ĭ. The figure shows the fast electron phase space electrons are streaming through a solid density target from left to right at close to the speed of light. Due to the heavy computational cost of these simulations, we write code to run on new accelerator hardware and traditional cluster supercomputers. and particle methods in multiple dimensions to study these effects in both electrons and ions. We have developed a number of codes that employ direct Fokker-Planck, expansion. How to correctly model these effects and use them in existing models is a challenging computational problem because of the disparate time and length scales involved and the need to correctly couple physics from multiple disciplines. The electron motion can be strongly affected by these fields, but short-range "collisions" between particles are also important. For example, the energy transferred to a plasma by ultra intense lasers is enough to generate large fluxes of relativistic electrons which stream through the plasma and set up complex electromagnetic fields. In a plasma, there may be deviations away from equilibrium on small length or time scales, or if the particles involved are very energetic. We are interested in kinetic effects in high energy density plasmas relevant to intense laser-plasma interactions and inertial confinement fusion schemes. We work on some of the most challenging problems in HEDP including multi-species plasmas, self-consistent emission, absorption, and scattering of radiation, non-equilibrium plasmas, the physics of inertial confinement fusion and investigations of fundamental quantum electrodynamic (QED) processes. Many other members of the plasma physics group also work on HEDP.Įxamples of our particular research interests are listed in more detail below. High energy density physics is the focus of a small team of theorists within the Plasma Physics group at Imperial College. HEDP plasmas include fusion plasmas, high intensity lasers, stellar interiors, early universe plasmas, and supernovae. Plasmas are very different to the other states of matter, and support an extremely rich variety of complex physical phenomena, which makes them compelling to study. A more technical definition is any volume with an equivalent energy density of 10 11 J/m 3 or more, or a pressure of 1 Mbar, or 1 million times Earth’s atmospheric pressure, and above.Īt these densities and energies, matter becomes plasma, also known as the fourth state of matter (the other three being solids, liquids, and gases). High energy density physics (HEDP) covers the interactions of matter with temperatures in excess of a million degrees C°, or densities from that of liquid water (1 gram per cubic centimetre) to many times the density of solid lead.
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