Tuesday, November 10, 2009

droplets for laser-driven fusion

11.09.09. Nuclear fusion is promising as a potential source of sustainable energy. When two deuterium nuclei (a deuterium nucleus consists of a proton bound to a neutron) fuse, for example, they can produce a Helium isotope (two protons bound to one neutron) and a bare high-energy neutron. The energy of these bare neutrons can be converted to consumable energy (for example by using the neutrons to heat water, produce steam, and drive turbines). Deuterium exists naturally, albeit rarely, in the form of deuterized water in the oceans, so the problem consists of extracting the deuterized water from the natural water and imbuing the deuterium nuclei with enough initial energy to fuse. A promising way of achieving this initial energy is by irradiating small droplets of the deuterized water with a powerful, fast-pulsed laser; in this case the diameter of droplet that maximizes fusion yield is in the 0.01 to 1 micron range. As an undergraduate I (Mr. Mugler) worked with Professor Tom Donnelly and other students at Harvey Mudd College to develop a controllable source of droplets of this size, an experience which featured prominently in my "path" (see previous post) from middle school to the present day. We used a piezoelectric oscillator to vibrate (at Megahertz frequencies) a column of fluid at its base, which produced from its surface an aerosol of micron-scale droplets whose diameter we characterized by measuring the scattering pattern of a laser shone through the aerosol (the diagram shown is from Donnelly et al, Phys Fluids, 2004). More recently, current Harvey Mudd undergraduates have brought the droplet source to the University of Texas at Austin, which houses one of the most powerful lasers in the world, and have successfully achieved laser-driven fusion with deuterized water droplets. For more information see a recent article in the Harvey Mudd College Bulletin.