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Details of Grant 

EPSRC Reference: EP/C531566/1
Title: Fokker-Planck simulations of transport and magnetic field generation in hohiraum laser-plasmas
Principal Investigator: Kingham, Dr RJ
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Physics
Organisation: Imperial College London
Scheme: First Grant Scheme Pre-FEC
Starts: 01 October 2005 Ends: 31 March 2008 Value (£): 120,670
EPSRC Research Topic Classifications:
Plasmas - Laser & Fusion
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:  
Summary on Grant Application Form
The interaction of intense laser pulses with plasma is an active area of research throughout the World. The leading motivation for this is the realization of inertial confinement fusion (ICF) for energy production and as part of the US stockpile stewardship programme. In ICF, small spherical pellets composed of deuterium and tritium are compressed and heated, using laser beams, to 1000 times liquid density and temperatures of over 100 million degrees Kelvin so that the nuclei fuse together liberating vast amounts of energy like in the Sun. The leading scheme for ICF is indirect-drive, whereby the millimetre diameter pellet is placed at the centre of a hollow gold cylinder (hohlraum). Multiple intense laser-beams (supplying 2 mega-Joules of energy in just one hundred millionth of a second) heat the inner surface of the cylinder which in turn emits x-rays. The intense bath of x-rays formed inside the cylinder, uniformly heats the outside of the ICF pellet causing it to implode.Now is a very exciting time for ICF as the National Ignition Facility (N IF) facility in the US and the Laser MegaJoule (LMJ) in France are nearing completion. However, some important physics, on which the success of ICF depends, is still not adequately understood. A prime example of this is heat flow by electrons in the ionized, hydrogen-helium 'gas-fill' placed inside the hohlraum to tamper ablation of gold plasma from the walls. Laser-plasma interaction in the gas-fill affects how the heater beams propagate to the walls. Instabilities can reflect light back (wasting laser energy) and deflect the laser beams (altering where they hit the walls, reducing the x-ray drive uniformity and ultimately the quality of the pellet implosion). Growth of these instabilities depends intimately on the state of the gas-fill, i.e. temperature, density, degree of ionization and flow speed, along the path of the beams. It is crucial to accurately know how heat flows in order to predict the state of the plasma.However addressing heat flow in the hohlraum is very challenging. The electron collisional mean-free-path (the distance an electron moves before scattering off another particle) is comparable to important scale lengths (e.g. width of the laser beams) which means that heat flows in an unusual way. The term for this is nonlocal heat flow. Also very strong magnetic fields develop where the lasers heat the walls and then flow into the gas-fill where they are expected to suppress heat flow. How magnetic fields develop and how they affect heat flow under the exotic, nonlocal conditions is not yet fully understood. Existing simulations use standard theories that are only valid when the mean-free-path is much smaller than the scale lengths. Therefore their results are questionable.The objective of this project is to investigate, for the first time, the processes of heat flow and magnetic-field generation in hohlraums, properly taking into account the nonlocal conditions. This requires an advanced simulation code that can treat kinetic effects and magnetic fields. We already have a Fokker-Planck simulation code that is kinetic, includes magnetic field and describes nonlocal effects to some extent. However nonlocal conditions in hohlraums are too extreme for this code. We will enhance our code to overcome this limitation. Initially we will investigate individual issues of importance to get an idea of the exotic physics that occurs. Eventually we will parallelize the code and perform more realistic, integrated simulations (with all the effects together) that give an improved picture of the temperature and magnetic field profiles in the hohlraum. The issues that we will address are of fundamental importance in their own right. The insights gained will be invaluable to other areas of laser-plasma physics.
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Organisation Website: http://www.imperial.ac.uk