Physics

Taming plasma turbulence to advance magnetic fusion energy

Who?

David Smith, Assistant Scientist
Department of Engineering Physics, University of Wisconsin-Madison
drsmith@engr.wisc.edu
http://homepages.cae.wisc.edu/~drsmith/

What?

Magnetic fusion energy is a promising energy development program with advantages like abundant fuel and carbon-free energy production not dependent on weather conditions.  To generate magnetic fusion energy, magnetic fields confine plasma (ionized gas) at high temperatures to initiate nuclear fusion reactions.  Plasma turbulence, one of the primary obstacles to fusion energy, can enhance the transport of heat and particles out of plasma and inhibit fusion energy production.  My research activities cover experimental and computation investigations of plasma turbulence to support the pursuit of magnetic fusion energy, and the results may lead to strategies for mitigating the undesirable effects of plasma turbulence.

How?

I develop scientific instruments that measure plasma turbulence in the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Lab (PPPL).  I presently work on a spectroscopic imaging system that measures deuterium emission imprinted with turbulence information, and the system includes optical components like fiber optics and photodiodes.  Previously, I developed a microwave scattering system sensitive to small-scale plasma turbulence using microwave components like waveguide and diode mixers.  When designing scientific instruments, I use tools like AutoCAD for mechanical design and OSLO for optical design.  In addition, I analyze data from experiments with scientific programming languages like Matlab or IDL, and I perform large computer simulations of plasma turbulence that run for several days on several dozen processors.  As scientists, we gain confidence in theoretical models when measurements and simulations show agreement.

Why?

Measurements from the spectroscopic imaging system are providing new insight into “edge” turbulence near the plasma boundary.  Plasma dynamics near the boundary impacts plasma performance and the heat load on plasma-facing components.  We have characterized edge turbulence and documented dependences on plasma parameters like density and temperature gradients.  We are beginning to compare experimental dependences with simulations.  Measurements from the microwave scattering system produced strong evidence for the existence of small-scale plasma turbulence driven by the electron temperature gradient.  Turbulence theories previously predicted that small-scale plasma turbulence can enhance the transport of electron thermal energy out of plasma.

Big questions to answer: Can a reasonably simple model capture the complex dynamics of plasma turbulence without the need for massive computer simulations?  Can optimized plasma configurations, plasma flows, or active control techniques suppress plasma turbulence or mitigate adverse effects?  Can magnetic fusion energy generate large-scale, sustainable power for society in the future?

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