Advanced pulsed power drive concepts for producing strong shocks in solids

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

One of the principle uses of large pulsed power facilities has been to magnetically accelerate cm-scale flyer plates to extreme velocities, then interact these with targets for equation of state studies. On the Z facility, for instance, aluminum flyers have been driven to velocities >40kms-1, and planar impacts with samples of carbon have produced >TPa pressures. Such flyers are the main method being explored by First Light Fusion to produce strong, planar shocks inside targets with an internal geometry designed to collapse and initiate fusion reactions.

Presently most magnetically driven flyer research is based around 'strip line' geometries, which are designed to optimize planarity of the flyer. However there are several other schemes - such as the ring launcher being explored at first light fusion and conically convergent schemes that redirect a magnetically driven implosion - which could be more suited to producing the required flyer acceleration/shape. Further, recent research has demonstrated that shock waves can be launched extremely efficiently by the current driven explosion of tamped wires - which could enable the shock waves to be produced in situ to any fusion target rather than via flyer.

This PhD studentship will explore new methods utilizing pulsed power to produce strong shock waves in targets. Starting with striplines, the student will explore how 3D shaping of the geometry - in particular the use of curvature - can be used to alter the launch and flight potentially enabling higher speed, smaller flyers to be launched. This work will be extended with the use of conically shaped imploding rods, with flyer launch from a small area at the end of the rod. Simultaneous to these new magnetic launch schemes, the student will examine the use of exploding wire loads to produce shaped high speed shock waves directly in a target material. Presently wires have only been exploded in water baths, and so this research will examine the use of plastics and metals around the wires, and explore new methods to further increase the speed of the shock waves produced.

The majority of this research will be carried out on the MACH generator at Imperial College - a cutting edge, ~2MA, 400ns pulsed power cavity that is dry air insulated. The student would be trained in the use of pulsed power, and designing and performing shock physics experiments utilizing multiple diagnostic techniques including multi-frame laser interferometry and Schlieren photography, streak photography, multiple point PdV, line VISAR and hard X-ray radiography using a portable X-pinch driver. They would also act to support the other FLF student working on MAGPIE with velocimetry measurements of the shock waves produced in experiments there (diagnostics not presently available on MAGPIE). In addition to exploring these new drive techniques the work will produce high quality quantitative data suitable for use and comparison to hydrodynamics codes.

Over the course of the PhD the student will be benefit from the good links already established between Imperial College and First Light fusion, enabling any research to be swiftly utilized by First Light.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 31/03/2022
1994036 Studentship EP/N509486/1 23/10/2017 31/10/2021 Savva THEOCHAROUS
 
Description Flyer plate acceleration using shocks coupled into water from underwater electrical wire explosion of a planar wire array has been demonstrated. Current results indicate velocities of around 1200 m/s using a 10 mm2, 1 mm thick aluminium flyer, with a peak current of ~600kA. The kinetic energy of these already appears to be well matched to flyers accelerated using the conventional, and already fairly well optimised, magnetic stripline technique with equivalent electrical characteristics. Side-on imaging and reflection diagnostics seem to indicate that the flyer surface remains solid and flat throughout the experiment. The use of a cavity to rebound the shock to drive additional acceleration, increasing efficiency, has also been demonstrated. Initial simulations and further experiments are in progress and x-ray radiography experiments are planned to investigate further the shocks from the planar wire arrays used to drive the flyers (all to be completed before the end of the award).
Exploitation Route The flyer acceleration could be optimised further, using alternative shock media to water, different flyer dimensions and material, different wire array configuration etc. The flyer plates could already be used to drive shock experiments with low current pulser systems, and would already be practical where non-conducting flyer materials might be desired, as the conventional method doesn't allow this.
Sectors Aerospace, Defence and Marine,Energy