PhD opportunities

Creating and probing extreme conditions with high power lasers

    • Type:  Experimental, with some simulations 

High power lasers can be used to create extreme conditions in the laboratory that are usually only found in extreme astrophysical environments.  Using short-pulse high power lasers my research group is trying to  create matter at temperatures and densities usually only found in the centre of stars and gas giant planets and use ultra-short flashes of X-rays to probe these; we can collide laser accelerated electron beams with high power lasers to measure the effects of very strong electromagnetic fields that can occur  on the surface of quasars; and we are attempting to  make X-ray fields that are so dense that photon-photon collisions, producing matter out of pure energy, something that can occur with intense gamma ray beams produced by massive compact objects.  By recreating and characterising such extreme conditions in the laboratory, we hope to increase our understanding of extreme astrophysical environments. 

    • Funding:               3,5 years fully funded via ERC grant (Home/EU students only)

For more information please contact Stuart Mangles.

Laboratory Astrophysics and High Energy Density Physics

PhD project for 2020 (subject to funding, see below)

Type: Experimental, including target and experiment design, and some simulations

High-Energy Density (HED) deals with matter at extreme states of density, temperature and pressure, very rarely encountered on Earth but very common in astrophysical phenomena. At these extreme conditions matter is usually in the ‘plasma’ state, a hot, ionised gas made of charged particles mediated by their electromagnetic fields. The ability to produce (and most importantly systematically reproduce) such plasmas on Earth-based laboratories has grown substantially thanks to technological advances in experimental plasma facilities such as high-power lasers and pulsed-power magnetic-field drivers. The combination of HED and laboratory experiments is the core of my research in ‘High Energy Density Laboratory Astrophysics’ (HEDLA), a cross-disciplinary area aimed at studying different aspects of space and astrophysical environments by the means of Earth-based laboratory experiments.

This PhD project will involve the design and performance of laboratory experiments in world class, high-power laser systems to study the formation of ‘radiative shocks’, shocks in which the main plasma parameters such as pressure, density and temperature are drastically modified by strong radiative losses, which only occur at shock speeds ~10-100s km/s. The project will involve learning about the physics at play, design of the experiments and targets (typically miniaturised gas-filled cells), use of different plasma diagnostics (e.g. X-ray backlighting imaging, optical emission imaging and spectroscopy) and the possibility of modelling these shocks with radiation hydrodynamics codes.

 Background reading:

-        T. Clayson et al., ‘Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors’, High-Energy Density Physics vol. 23: 60-72 (2017).
https://www.sciencedirect.com/science/article/pii/S1574181817300198

-        R.P. Drake et al., ‘Radiative shocks in astrophysics and the laboratory’, Astrophysics & Space Science vol. 298: 49-59 (2005).
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/42041/10509_2005_Article_3911.pdf?sequence=1&isAllowed=y

Funding: Subject to funding (for instance Imperial College President’s Scholarship, Departmental EPSRC DTA, self-funding)

For more information, please contact Dr Francisco Suzuki-Vidal

Keywords: Experimental plasma physics, high-power lasers, radiation hydrodynamics, plasma diagnostics, target design, numerical simulations 

 

 

Modelling the effects of radiation and magnetic fields on shocks and turbulent flows in laboratory astrophysics experiments

 
Laboratory astrophysics provides a mechanism to test our understanding of the behaviour of astrophysical bodies by using dimensional scaling to design laboratory experiments which behave in a similar manner. Such experiments must be carefully designed to replicate the physical processes which make the non-linear evolution of supersonic flows in dense astrophysical plasmas very different to that found in conventional fluid dynamics. The intense X-ray radiation generated within shock fronts allows the plasma to cool, making it more compressible and collapsing the shock until it becomes too thin to remain hydrodynamically stable. This process is believed to contribute to the break-up of expanding blast waves which form supernovae remnants. Transport and reabsorption of some of this X-ray radiation produces a ‘precursor’ propagating ahead of the shock discontinuity which fundamentally changes the nature of the shock front. Strong density and temperature gradients at the shock front or elsewhere in the plasma can also be the source of spontaneously generated magnetic fields which are thought to be a possible candidate for the first ‘primordial’ magnetic fields generated within the universe. Compression of these fields can lead to strongly magnetised flows which again modify the nature of the shock as is the case in the Earth’s magneto-spheric bow-shock. Magnetic fields can also be responsible for the development of instabilities within supersonic flows, leading eventually to turbulent magnetised flows which again have very different properties to turbulence in conventional fluid dynamics.
Experiments designed to replicate these processes in the laboratory, typically require the use of large scale lasers or pulsed power generators in order to achieve the high energy density plasma states required. Recent work has included the use of the Orion laser to produce radiative blast waves and the use of the 1.5MA Magpie generator at Imperial College to investigate magnetic reconnection in supersonic flows. The principle computational tool which enables the design of new experiments on Magpie and other pulsed drivers is the Gorgon 3D magneto-hydrodynamics tool which was developed within the Plasma Physics group at Imperial College.
This PhD studentship will involve the adaptation of the Gorgon code to new laboratory astrophysics configurations to enable the study of the effects of radiation and magnetic fields on the stability of blast waves, particle acceleration in processes in magnetised shocks, studies of magnetically decelerated supersonic flows and the compression of turbulent magnetised plasmas. The work will involve the continued development of elements of the core MHD model as well as post-processing models which generate ‘synthetic diagnostics’ to facilitate comparison to experimental data. The student will be expected to collaborate with experimental groups at Imperial College, Cornell University, UCSD and Sandia National Laboratories as well as computational and theoretical groups at the Universities of Rochester and Paris VI.
Background reading
B.Remington, Plasma Phys. Control. Fusion 47 A191 (2005) doi:10.1088/0741-3335/47/5A/014
F. Suzuki-Vidal, et. al. Phys. Rev. Lett. 119, 055001 (2017) doi: 10.1103/PhysRevLett.119.055001
M. Bocchi, B. Ummels, J.P. Chittenden, et. al. The Astrophysical Journal 84, p767 2013 (doi:
10.1088/0004-637X/767/1/84)
J. Hare Phys. Rev. Lett 118, 085001 (2017) doi: 10.1103/PhysRevLett.118.085001

Shocks and transition to turbulence in magnetized high density plasmas

Type:   Experimental, including development of diagnostics

Shock waves are important feature of many magnetised plasmas in astrophysics, in space plasmas and in laboratory plasmas relevant to Inertial Confinement Fusion research. We are recruiting a student to join our experimental team working on the 1.4MA MAGPIE pulsed power facility at Imperial College.  The PhD project will be focused on the studies of the shock waves formed in the interaction of supersonic plasma flows with various obstacles. Of particular interest will be investigations of the development of instabilities in the shocks, in conditions scalable to astrophysical shocks.  The project could also involve studies of the development of turbulence in rotating plasmas. Work will involve modification of the already existing experimental set-ups, designing appropriate targets allowing quantitative characterisation of the shocks, and designing and testing of new experimental configurations. The project will also involve the development and implementation of advanced plasma diagnostics, such as Thomson scattering, interferometry, optical and x-ray imaging and spectroscopy and X-ray radiography.

Background reading:

G. C. Burdiak et al., Physics of Plasmas 24, 072713 (2017).

J.D. Hare et al., Physical Review Letters 118, p. 085001 (2017)

Funding: Departmental studentship (pending)

 Supervisor: Sergey Lebedev