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EPSRC Reference: EP/C008359/1
Title: Coupled multi-scale modelling of magnetic reconnection
Principal Investigator: Arber, Professor T
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Department: Physics
Organisation: University of Warwick
Scheme: Standard Research (Pre-FEC)
Starts: 01 October 2005 Ends: 30 September 2009 Value (£): 86,278
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Summary on Grant Application Form
At high temperatures gases become ionised so that the electrons and ions are separated. Such a gas, called a plasma, is the most common state of matter in the universe. When a magnetic field is embedded in a plasma it behaves in many ways like a stretched elastic band. Under certain conditions these 'elastic' magnetic field lines can break and reform in new shapes. This processes is know as magnetic reconnection. When it occurs there is usually a very rapid release of energyand some particles are accelerated. This occurs for example in solar flares, the magnetic reconnection which causes polar aurora and also in devices aiming to control thermonuclear fusion for commercial exploitation as a power station. Thus the process of magnetic reconnection is a basic process in the most common state of matter whose study is of fundamental importance in subjects ranging from astrophysics to the possible next step in power production. The proposed power station based on controlling a plasma, called a tokamak, is the subject of a multi-billion pound international collaboration (ITER) which if successful could lead to a power source which produces no greenhouse gases, is effectively inexhaustible and producesnone of the long lived radioactive waste associated with conventional nuclear power.There is a major computational problem when trying to write programs to help us understand what happens during magnetic reconnection. What we must do is solve for the properties of the plasma at a finite number of points in space: a finite grid. This is because there is a limit to theamount of computer memory available even on national supercomputers. Solving the simplest model, called magnetohydrodynamics or MHD, on a three dimensional grid with 1000 points in each direction would typically require 100 to 200 GBytes of RAM. However, the reconnection process often occurs on very small scale lengths and thus we would need 100,000 points in each direction to resolve this process in our computer codes. This would require one million times 100 GBytes of RAM and easily exceeds the memory in the largest computers in the world. One solution is to use a smarter code. Such codes only include extra grid points in regions near the reconnection. Warwick Universityhas recently developed such an adaptive mesh refinement (AMR) code for MHD. Unfortunately, this still leaves a number of computational, and physics, problems to be addressed before full computer simulations of magnetic reconnection are possible.1. AMR codes have a complex data structure which makes it harder to get these codes to work efficiently on modern parallel computers. The first part of this project would be to implement a simple strategy for running the existing AMR code on a large parallel computer.2. Once we get close to resolving the very short scales we need to study magnetic reconnection it turns out the the simple model of MHD is no longer valid. We must actually begin to resolve the motion of plasma particles themselves. We must therefore couple the MHD code to a different computer model, a so called kinetic model, on very fine scales. While using AMR has solved the problem of computer memory as soon as we couple to kinetic models this problem immediately needs a massive parallel computer to run. The second, and major, part of this project is to couple the AMR MHD code to a kinetic model (Vlasov solver) and to efficiently optimise this code for modern parallel computers.3. The datasets from these simulations will be massive so effort must also be put into visualisation tools once the code has been run.This project therefore involves the student combining two computer codes and optimising the resultant code for national supercomputers. When complete this will enable us to perform world leading computer simulations of a fundamental plasma process.
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Organisation Website: http://www.warwick.ac.uk