Plasma PhD Projects for October 2016 Start

Laboratory astrophysics: acceleration of electrons in magnetized plasma shock waves

Title  Laboratory astrophysics: acceleration of electrons in magnetized plasma shock waves
Supervisor Professor Sergey Lebedev
Description  In this project we will use a combination of the Imperial College MAGPIE Z-pinch and Cerberus laser systems to create scaled laboratory models of some of the astrophysical processes. The overall objective is to investigate the acceleration of particles by shock waves in magnetised plasma in conditions relevant to the acceleration of cosmic rays.
View Document (Laboratory astrophysics)
Funding Firmly Funded DTA

Understanding limitations to hotspot confinement by exploiting multiple synthetic diagnostic methods

Title  Understanding limitations to hotspot confinement by exploiting multiple synthetic diagnostic methods
  80% computational 20% experimental
Supervisor Professor Jeremy Chittenden
Description  The project seeks to understand the departures from symmetry which are principally responsible for limiting fusion performance in inertial confinement experiments on the National Ignition Facility. The work will involve making use of a comprehensive set of diagnostic data from NIF to constrain possible sources of 3D perturbation in radiation hydrodynamics simulations of asymmetric implosion and stagnation.
View document (Understanding limitations ...)
Funding Funding TBD

Rad-hydro modelling of hohlraum energetics including VFP electron transport

Title  Rad-hydro modelling of hohlraum energetics including VFP electron transport
Supervisor Dr Robert Kingham
TYPE Computational & Theoretical
 Description  

The goal is to improve the treatment of electron thermal transport under the extremely non-equilibrium conditions found in indirect-drive ICF.  This will be achieved by coupling a 2-D kinetic code for electrons (the Vlasov-Fokker-Planck code IMPACT) to LLNL’s radiation-hydrocode HYDRA. The coupled code will allow  –  for the first time  –  proper assessment of the role of non-local effects and kinetic B-field dynamics in an integrated way on the hohlraum gas-fill, ablated wall plasma, and x-ray source at the wall in 1D and then 2D.

Funding Funding TBD
   

Modelling kinetic effects in transport in the tokamak scrape-off-layer

Title  Modelling kinetic effects in transport in the tokamak scrape-off-layer
Supervisor Dr Robert Kingham
TYPE Computational & Theoretical
 Description  

This project will address electron transport in the scrape-off-layer (SOL) where plasma exhausting from the core streams down ‘open’ magnetic field lines that spiral to the wall. Fluid models have struggled to correctly describe particle and heat fluxes here. Very recently 1D kinetic modeling has been attempted but lacks self-consistent electric field. This PhD project will build upon this by adding self-consistent electric fields and incorporating the effect of the plasma boundary conditions into the model. This will be achieved by adapting an existing kinetic simulation code.  This will inform the theory part, with the goal of deducing a reduced analytic model that captures the key characteristics of kinetic transport but is tractable enough to incorporate in 2D or 3D SOL fluid codes.

Funding Funding TBD

Development of compact laser accelerators

Title 
Development of compact laser accelerators 
Supervisor
Professor  Zulfikar Najmudin
 Type
 Experimental (may include simulational work)
 Description  

Laser wakefield accelerators have the prospect to become the next generation of particle accelerators. A high intensity laser pulse generates a large amplitude plasma wave, which can accelerate particles at a rate more than thousands of times faster than conventional accelerators. As well as making the next generation of linear accelerator for high energy physics possible, this type of accelerator can have a range of other applications in technology and science. This studentship will investigate the development of a compact system that can generate electron beams in the 100’s MeV energy range in the basement of the Blackett Laboratory. This system would be tested for a number of applications including generation of high energy particles and a driver for intense radiation and other light source applications.

Funding DSTL case studentship (pending)

Investigation of infrared lasers for efficient acceleration of ion beams

Title 
Investigation of infrared lasers for efficient acceleration of ion beams
Supervisor
Professor  Zulfikar Najmudin
 Type
 Experimental (may include simulational work)
 Description  

Intense lasers can generate intense beams of ions through a number of mechanisms. Amongst the most promising is the creation of energetic ions through reflection from collisionless shocks generated in low density targets by the extreme light pressure (or heating) of an intense laser pulse. Infrared lasers are a particularly interesting driver of this interaction as it allows the use of lower density plasmas. New advances in IR laser development (both here at Imperial College and at the ATF Brookhaven National Laboratory) promise the possibility of performing these experiments for the first time at intensities > 1018 Wcm-2. This should allow a major advance in the energy of ions that is achieved, for example reaching proton energies exceeding 100 MeV. Such beams would have considerable interest for applications such as radiation treatment of tumours or for fast heating of fusion capsules.

Funding Departmental studentship (pending). 

Time resolved X-ray absorption studies of Matter in Extreme Conditions

Title 
Time resolved X-ray absorption studies of Matter in Extreme Conditions
Supervisor
Dr Stuart Mangles
 Description  

Much of the visible universe exists in extreme conditions, for example at high pressures and  temperatures inside stars and gas giant planets or in the presence of intense xray fluxes (eg the low density gas near black holes).   Much of our understanding of these systems comes from detailed atomic physics calculations.  However testing these models experimentally is very challenging -- such extreme conditions can now be created in the lab but only for very short periods of time (~ 1ps).
One of the ideal ways to study the atomic physics of these highly transient lab systems under extreme conditions is to use X-ray absorption spectroscopy, and the ideal X-ray source would have a broad spectrum (to allow absorption features to be observed) and femtosecond duration (to freeze the transient behaviour).  Our group has pioneered the development of X-ray radiation from laser wakefield accelerators which uniquely has both these properties.
As part of the TeX-MEx project (recently funded by the ERC) we have two fully funded PhD positions.

The first  project (co-supervised by Ed Hill) will develop atomic physics models used to describe these systems and will work closely with our experimental team to aid the design and interpretation of experiments and refine the atomic physics models using experimental data.

The second project will join our experimental team  developing our X-ray absorption spectroscopy program, designing, running and analysing experiments at national and international facilities such as the Astra Gemini laser at the Rutherford laboratory and the LCLS X-ray free electron laser in California.  These experiments will use the unique properties of betatron radiation to probe of some of the most extreme conditions in the universe.

Funding 2 ERC funded projects

The Design of New Inertial Confinement Fusion Targets

Title 
The Design of New Inertial Confinement Fusion Targets
Supervisor
Professor  Steven Rose
 Type
 

Theory & Computational

 Description The aim of the project is to design, mainly using a 1D radiation-hydrodynamics model, an inertial confinement fusion target that could be fired on the US National Ignition Facility laser with the aim of producing 100kJ output. Although that output represents an energy gain of approximately 1/20 (thermonuclear energy out / laser energy in), that would still be a factor of ten improvement over current results.  The best available microphysics models will be incorporated into an existing 1D code.  A number of different and new target designs, using simple design principles, will then be analysed.  The best will then be further scrutinised using cutting edge multi-dimensional codes, with the view to fielding on actual experiments.

ROSE PhD Studentship 1

Funding TBC

Opacity and radiation transport in the ablator of inertial confinement fusion targets

Title 

Opacity and radiation transport in the ablator of inertial confinement fusion targets

Supervisor
Professor  Steven Rose
 Type
 

Theory & Computational

 Description

There are 3 aims: (1) Improving the non-LTE opacity/emissivity modelling of radiation transport, particularly for the outer part of the spherical capsule in the context of indirect-drive ICF. (2) Exploring moving away from the opacity/emissivity modelling approach to the modelling the photon spectrum directly, particularly for current C and Si ablator designs.  (3) Adding in the effect of velocity gradients.

ROSE PhD Studentship 2

Funding TBD

High-intensity laser interactions with levitated microtargets

Title 

High-intensity laser interactions with levitated microtargets

Supervisor
Professor  Roland Smith
 Type
 

Experimental 80%, computational 20%

 Description

Completely isolated few micron objects have unique properties that make them a compelling target for high energy density physics experiments.  As an intense, sub-picosecond laser diffracts around a "small" wavelength scale target, interference between the incoming and scattered light produces large electric field enhancements that accelerate electrons to high energies and drive them back into the target.  Once the small mass of the target begins to heat up to a temperature similar to that of the core of a star, the lack of a physical connection to cold material clamps both conductive cooling and the region x-rays can be emitted from.

The lack of a physical support also eliminates electrical current paths into and out of the target, radically modifying the charge up dynamics, and confining "hot" electrons.  This has several important consequences, hot electrons cannot drive x-ray emission in a support stalk that might otherwise reduce resolution in an imaging application, and charge captured by the surrounding vacuum chamber cannot rapidly return to the target, greatly limiting unwanted electromagnetic pulse (EMP) generation.  Both of these are key points for applications such as x-ray imaging of inertial fusion implosion experiments at the National Ignition Facility in the US.

After several years of work we have now solved the key technical challenges necessary to allow a micro-target source to be shot with a large scale laser system.  We have developed a unique long working distance optical levitation trap which uses photon momentum transfer to space-fix small objects.  "Traditional" optical traps operate in a fluid medium at distances of ~1mm using microscope lenses that can be easily damaged by scattered high-intensity laser light.  In contrast our system uses a levitation technique that is fully vacuum compatible and traps ~10um objects at long working distances of ~40mm for long timescales.  Unlike electrostatic traps our more elegant optical system does not require a surrounding mechanical structure and so has excellent "visibility" for experiments and applications.  The trap is designed for use in the very harsh environment of a killoJoule class laser interaction and will be used at the Vulcan Petawatt laser in April-May 2016.

A major component of the PhD project will be experimental, focusing on developing x-ray imaging applications of levitated microtargets and improving trap systems and remote in-vacuo loading techniques. The trap will be used with multi-terawatt lasers to create isolated microplasmas and then explore their x-ray and particle imaging and EMP characteristics as a probe of transient high energy density plasmas.  This will be supported by numerical modelling of the interaction of high-intensity laser light with microtargets and the acceleration of ions and electrons to multi-MeV energies in this unique experimental geometry.

 

Funding

Proposal under consideration by LLNL

X-ray probing of shock compressed matter under extreme conditions

Title 

X-ray probing of shock compressed matter under extreme conditions

Supervisor
Professor  Roland Smith, Dr Dan Eakins and Dr Simon Bland
 Type
 

Experimental 80%, computational 20%

 Description

Supersonic gas gun and high-power laser driven shocks can heat and compress matter to the extreme conditions of temperature and pressure found inside Jovian planets or the early stages of an inertial fusion experiment.  The physics of such "warm dense matter" is complex and challenging to both measure and model.  The aim of this project is to develop and exploit new x-ray techniques to enable probing of processes such as pressure driven phase changes and the dynamics of material failure that happen deep within a macroscopic shocked object.  These will be linked to state of the art numerical models and used to test and refine computer simulations. 

Shocks will be driven into sample materials using a combination of supersonic gas guns and high-energy laser systems which evolve on picosecond to microsecond timescales.  To "freeze" and capture the dynamics of these systems we will exploit the ability of sub-picosecond lasers to create high-brightness x-ray sources and compare these to pulsed power systems such as x-pinches and advanced light sources including free electron lasers. 

Funding

EPSRC CASE industrial conversion proposal.

Improved tokamak dust transport simulations

Title 

Improved tokamak dust transport simulations

Supervisor
Dr Michael Coppins
 Type
 

Computational

 Description

Our DTOKS (Dust in TOKamakS) code simulates the motion and lifetime of tokamak dust produced by the erosion of plasma facing walls. It has been used to study various tokamaks including MAST, JET and ITER. At present the code assumes that the background plasma, through which the dust grains move, is constant in time. This project would involve upgrading the code to allow for time dependent plasmas. In addition, there are several other improvements which need to be made to the code’s basic physics model. These would be based on our recent work on dust-plasma interactions, and would include the charging of large and non-spherical dust grains, magnetic field effects, and misty plasma effects. Once upgraded the code would be used to study dust transport during ELM crashes.

Funding

No specific funding attached to this project, but may obtain a Departmental DTA award

Voids in dusty plasmas

Title 

Voids in dusty plasmas

Supervisor
Dr Michael Coppins
 Type
 

Theoretical/Computational

 Description

Much work on dusty plasmas focuses on collective phenomena in which a large number of plasma-immersed, monodisperse dust grains interact to produce complex structures. Amongst the most striking of these phenomena are the voids, dust free “bubbles” with sharp boundaries, which occur in microgravity (e.g., on the International Space Station). This project involves developing a new theoretical picture of void formation, which would include the existence of a double-layer at the void surface. In addition, it has been proposed that dust grains in a plasma experience an inter-grain attractive force, although this has not been conclusively proved experimentally. Such a force would introduce an effective surface tension which would affect the void. By including this effect in our model we could possibly propose experiments using voids to determine the nature of this attractive force.

Funding

No specific funding attached to this project, but may obtain a Departmental DTA award

3D Laser Printing New Materials for Extreme Environments

Title 

3D Laser Printing New Materials for Extreme Environments

Supervisor
Dr Daniel Eakins, Dr David Chapman, Dr Paul Hooper
 Type
 

Experimental

 Description

Our ability to manipulate structure and chemistry at progressively smaller length scales has led to a broad class of complex, heterogeneous material systems. The high strain-rate behavior of these materials is an example of an important area of study, owing to the innumerable applications for materials in dynamic environments. The capacity to predict the physical, mechanical, and chemical behavior of such systems subjected to extreme conditions relies upon understanding of the influence of these heterogeneities on phenomena such as compressibility, strength, and physical/chemical changes. This knowledge will provide the capability to predict the response of multi-component, heterogeneous materials, and ultimately aid in the design of materials with tailored mechanical and chemical properties.

 This PhD studentship will investigate the bottom-up prediction and control of advanced materials fabricated through laser-selective melting (“3D printing” for metals). Using the ISP’s world-class suite of gas-gun, laser, and magnetic loading platforms, this experimentally based PhD project will systematically study the behaviour of key metals/alloys subjected to a broad range of extreme loading conditions, such as those that would be experienced during aircraft jet engine failure, during meteorite impacts, or laser-driven shock. The overall emphasis is on identifying key deformation mechanisms for improved processing/microstructure/property relationships.

 This multi-disciplinary project will link to ongoing research investigating the quasistatic to low-rate mechanical properties of AM materials within the Centre for Manufacturing Studies (CEMS) and Mechanical Engineering at Imperial College.

Goals and Outcomes

The primary outcomes of the research will be:

  1. a parametric study into how different initial build parameters (laser energy, spot size, raster pattern, etc.) in a commercial additive manufacture machine affect the final microstructure of an AM component.
  2. new understanding of the comparative bulk equation-of-state and constitutive properties of both AM and CM materials subjected to a range of loading conditions
  3. identification of the dominant deformation mechanisms operating at the mesoscale as a result of various AM microstructures.

 Significance and Impact

 The results of these experiments will supply new data on an emergent class of materials needed to develop models describing their constitutive behaviour under a wide range of loading scenarios. With sufficient knowledge of structure/property relationships, this in turn will lead to a future capability for fabricating advanced materials capable of withstanding the most extreme environments.

Funding

Fully Funded