Current PhD opportunities
Inertial confinement fusion using laser driven and wire array Z-pinch driven hohlraums
Supervisor Prof. Jeremy Chittenden
One of the main approaches to inertial confinement fusion (ICF) is ‘indirect drive’ where lasers or X-ray sources are used to heat a cylindrical cavity called a ‘holhraum’ which surrounds a spherical capsule containing the fusion fuel. This hohlraum is typically heated to several million degrees Centigrade at which point the inner surface acts as a black body radiation source. The X-rays emitted by this black body then bombard the capsule causing the surface to expand rapidly. The reaction force due to this surface expansion causes the interior of the capsule to implode, compressing the fusion to very high densities and heating it to fusion temperatures.
Much of the recent work investigating the use of hohlraums in indirect drive ICF has taken place on the National Ignition Facility laser at Lawrence Livermore National Laboratory. Recent experiments have concentrated on trying to achieve the process of ‘ignition’, where alpha particles heat the plasma and enhance the energy yield. Plasma pressures inside the capsule reaching half the value required for ignition have been demonstrated along with significant levels of alpha particle heating. One of the factors currently thought to be inhibiting further increases in fusion yield is a lack of symmetry in the radiation from the hohlraum reaching the capsule. There are a number of potential causes for this, such as the non-uniform expansion of the inside wall of the hohlraum that occurs as it is heated by the laser. In addition, the extreme plasma density and temperature gradients that exist within the hohlraum are thought to be a source of spontaneously generated magnetic fields which can strongly affect the uniformity of the black body temperature distribution that is obtained.
An alternative to the use of lasers to heat the hohlraum is to use X-ray sources from magnetically driven implosions. One such scheme uses a cylindrical target formed from an array of fine metallic wires which is imploded using the electro-mechanical force from a pulsed electrical driver with several mega-amperes of current. This ‘wire array Z-pinch’ plasma provides a highly efficient X-ray source which can in turn be used to heat a larger scale hohlraum and capsule than is used with laser driven indirect drive. This approach provides a potential means of realising plasma ignition on a larger scale plasma with substantially higher fusion yields.
This PhD project will involve large scale high performance computing simulations of laser driven and wire array driven hohlraums using the 3D radiation magneto-hydrodynamics code ‘Chimera’ developed at Imperial College. One of the principle objectives is to undertake the first comprehensive three-dimensional treatment of the effects of magnetic fields on radiation symmetry in laser driven hohlraums. Further simulations will investigate potential future designs for wire array Z-pinch driven hohlraums. This work will also involve modelling in-house experiments on the Magpie pulsed electrical generator designed to study the ablation of materials using X-ray pulses from imploding wire array Z-pinches.
The project will be based within the Centre for Inertial Fusion Studies at Imperial College and will involve close collaborative work with experimental groups at Lawrence Livermore National Laboratory and Sandia National Laboratory as well as the Magpie group at Imperial.
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