The public version of my thesis presentation is a seminar on Monday, which I will be broadcasting LIVE on livestream.com/halfriesen. I’ll also have the video embedded on this site so you can watch it here as well. You can watch and type comments for those of you who can’t make it in person. For those of you who are in Edmonton, I can’t think of anything you’d rather be doing besides hearing about fusion research, so here are the time & place details. Hope to see you there!
Area of Interest: Plasmas and Photonics
Supervisors: Dr. Robert Fedosejevs and Dr. Ying Tsui
Date and Time:
Monday, August 22, 2011
1:30 – 2:30 PM
Seminar Title: Kirkpatrick-Baez Microscope for Hard X-Ray Imaging of Fast Ignition Experiments
In the burning ionized gases of the Sun, with temperatures of a million degrees Kelvin and pressures on the order of megabars (a million atmospheres), atoms are pushed close enough to one another that the Coulomb repulsive barrier can be overcome in order to form a new nucleus. This process, nuclear fusion, is the way that heavier elements are generated from the abundant hydrogen in the universe.
The nuclear reaction of combining deuterium and tritium to form helium and a neutron, products with a net energy of 17.3 MeV, is one that occurs on the sun and is the goal of many clean-energy minded scientists. Huge output energy, non-toxic byproducts, plentiful supply of deuterium in the ocean and tritium that can be bred on-site are just a few of the reasons why the desire to reproduce fusion on Earth is so strong. In contrast to nuclear fission, it produces no long-term radioactive waste, and unlike other energy schemes, fusion produces no greenhouse gases.
Currently there are two broad categorizations of approaches to create fusion energy, separated by the way in which the fuel is kept together: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF). The basic idea behind magnetic confinement is to use magnetic fields to confine the fuel for long periods of time and thus maintain the close proximity necessary for fusion while preventing it from cooling by contacting the walls. The idea behind inertial confinement is to push the fuel together to fuse faster than it can separate, capitalizing on the fact that the pellet has an inertial mass that will require a finite time to disassemble.
One promising ICF method to produce net gain is fast ignition which decouples the compression and ignition in normal ICF schemes. One technique for fast ignition relies on hot electron transport to heat the core to the critical temperature.
Hot electron transport is investigated through placement of tracer layers in the target that produce characteristic K-alpha x-rays when an electron knocked out from the 1s shell is replaced by one from the 2p shell. Imaging these x-rays is challenging, and requires a resolution of a few microns over a field of view of several hundred microns. The grazing-incident Kirkpatrick-Baez mirror design can meet these requirements.
This thesis project involves the construction and characterization of a suitable KB microscope for use in experimental runs on the Titan laser at LLNL. A re-entrant design is employed which allows for alignment from outside the chamber. A bilayer coating of Cr/Pt with a low grazing angle of 0.5 degrees provides higher resolution than a pinhole and a wide enough bandwidth to image thermally-shifted characteristic K-alpha emission from heated Cu tracer layers in Fast Ignition experiments. The superpolished substrates (<1 Angstroms rms roughness) were coated in the University of Alberta nanofabrication lab and shown to retain a roughness of 1.7 Angstroms after coating. A unique feature of this design is that during experiments, the unfiltered zero-order signal along with one-dimensional reflections are retained on the detector in order to enable a live indication of alignment and incident angle. The broad spectral window from 4 to 9 keV enables simultaneous observation of emission from several spectral regimes of interest, which has been demonstrated to be particularly useful for cone-wire targets. A theoretical resolution smaller than 30 microns over a 300 micron field of view has been confirmed experimentally, with a peak resolution of 15 microns.