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Ph.D.
1980 University of London (Queen Mary College)
Research Areas: |
Neutral and Charged Particle Transport Theory, Atomic Collisions in Solids Modelling, Plasma-Surface Interactions and Tokamak Edge Plasma Physics |
Description of Research: |
The interaction of energetic radiation with
matter is a ubiquitous phenomenon with beneficial consequences and undesirable
manifestations. For instance, high energy cosmic ray particles consisting
of protons, helium ions and a range of heavy ions, are constantly bombarding
the earth's atmosphere and give rise to a host of secondary particles such
as electrons, photons and muons. Collectively, these radiations present
a hazardous environment for sensitive satellite components as well as for
astronauts and high altitude frequent fliers. On the other hand, accelerator
produced energetic electrons and photons are routinely used in radiation
therapy treatment of cancer, and the potential of heavy ion radiotherapy
is currently being evaluated globally. Likewise, ion implantation is a critical
process in the microelectronic industry as a means of introducing dopants
into semiconductors for use in computer chips, lasers, etc., but radiation
damage occurs as an undesirable side effect. Plasmas are used in industry
for etching and for producing thin film coatings but plasma-surface interactions
cause deleterious effects in magnetic fusion devices. The focus of our research
program is on theoretical and computational modelling of the interaction
and transport of energetic radiation in matter using linear transport theory.
Specific investigations are briefly outlined below. The Boltzmann Fokker-Planck formalism is used to describe charged particle transport in the presence of highly forward peaked scattering. Numerical solutions are constructed using linear and nonlinear (exponential) discontinuous finite element methods to investigate energy and charge deposition distributions. A unique cross section library for arbitrary ion mass - target atom interactions in the few keV to few MeV., Coulomb dominant energy range has been developed for coupling with the MCNP transport code to investigate multi-dimensional ion implantation and radiation damage in amorphous media containing lateral heterogeneities. Analytical techniques, such as asymptotics, projection methods, and the maximum entropy method, are used to complement the numerical work, in particular in the spatial and angular spreading of pencil beams of charged particles. We have considerable interest in stochastic transport theory. We are using the Master equation approach to investigate fluctuations that arise due to intrinsic branching processes. Applications include relativistic heavy ion fragmentation collisions, sputtering phenomena, and charge state fluctuation during slowing down of energetic ions. We are also interested in describing transport in media with highly complex structure by introducing space-time stochastic cross sections into the transport equation and developing exact and approximate closure schemes. Applications include transport of neutral atoms in plasmas, and radiative transfer in cloud and stellar atmospheres. Other miscellaneous research areas include numerical investigation of drift-diffusion equations in drift dominant regimes, fluid modelling of edge plasmas, and radiation effects in electronic materials. Agencies that have funded this work include Department of Energy, Los Alamos National Laboratory and Sandia National Laboratories. . |
