New Applied Physics Faculty

The Applied Physics and Applied Mathematics Department is pleased to welcome two new assistant professors of applied physics: Andrew J. Cole and Francesco A. Volpe.

Andrew J. Cole is a new Assistant Professor of Applied Physics.

Prof. Cole studies the influence of symmetry-breaking magnetic fields on rotation in toroidal fusion plasmas. Magnetic perturbations with spatial variation and field line curvature induce forces on plasma particles which collectively drive a viscous stress. In toroidal geometry this produces a torque which has the interesting ability to drive the bulk plasma rotation to a value proportional to the ion temperature gradient. In particular, plasmas with little or no rotation can be accelerated up to the ion temperature gradient rotation rate.

Rotation is generally stabilizing against a host of plasma instabilities, and magnetic torques offer an inexpensive and attractive means to induce rotation. A general spectrum of applied fields will naturally have some components which are resonant within the plasma. These perturbations have long been known to drive plasma tearing-modes, named for their ability to tear and reconnect magnetic field lines. This magnetic reconnection produces potentially large “magnetic islands” that allow heat and particles from the hot fusion core to contact cooler edge plasma. Magnetic islands limit fusion performance, and if large enough, can trigger a complete loss of plasma confinement.

Prof. Cole’s research into magnetic field-driven torques spans both non-resonant bulk plasma viscosity and resonant torques, the latter resembling AC-induction motor behavior and confined to their respective resonance surface. Interest in plasma torques is motivated by the need to generate stabilizing rotation in future plasma devices which will lack present costly methods of injecting angular momentum.

He received his Ph.D. in Physics from the University of Texas under the supervision of Prof. Richard Fitzpatrick, studying two-fluid effects on magnetic reconnection. More recent work at the University of Wisconsin as a postdoctoral fellow, and later assistant research scientist, involved studying the effect of non-resonant viscosity on magnetic reconnection and developing analytic connection formulas for non-resonant viscosity over a wide range of plasma parameters. This work was in collaboration with APAM alumnus, Prof. Chris Hegna (Ph.D. 1989, Plasma Physics), and Prof. James Callen.

Francesco A. Volpe is a new Assistant Professor of Applied Physics.

He joined the faculty in January 2012 from the University of Wisconsin, Madison, where he was an assistant professor in Engineering Physics. His research interests include plasma physics and nuclear fusion in toroidal magnetic confinement devices such as tokamaks and stellarators. In particular, Volpe focuses on two aspects which are key to fusion energy. The first consists in keeping the plasma sufficiently hot for the ions to fuse (and thus liberate energy) in spite of their Coulomb repulsion. The second aim is to keep the plasma in a high-pressure state (yielding high fusion power) and prevent it from degenerating in a reduced pressure state or, worse, to be deconfined. Such a rapid and complete loss of confinement is called disruption. It is not dangerous for people but can damage the tokamak device. Volpe uses microwaves both for the purpose of heating the plasma as well as for the purpose of suppressing or preventing structures called magnetic islands, which lower the plasma pressure and often lead to disruptions. He also uses magnetic fields to control the rotation of such islands, or reposition them, if they stop rotating in a position which is inaccessible to the microwave beams. As a complement to the injection of high-power microwaves in the plasma for the sake of heating, he also analyzes spontaneous low-power emission from the plasma, and so infers its temperature, especially in high-density regimes when this would not be possible, normally. For this, he uses special waves called Electron Bernstein Waves. Surprisingly, the underlying mechanisms of all these techniques are not very different from the principles by which a microwave oven heats water and a compass is steered by a magnet, and we can tell the temperature of the surface of the Sun by analyzing its emission.

Volpe is a recipient of the Otto Hahn Medal of the Max Planck Society and of the Early Career Award of the DOE. He received his laurea in Physics from the University of Pisa, Italy, writing a dissertation on undergraduate research carried out at ENEA Frascati. He obtained his Ph.D. in Experimental Physics in 2003 from the University of Greifswald, Germany, carrying out his thesis research at the Max-Planck Institut in Garching. Between these two experiences and subsequent postdoctoral training in the U.K. and in California, and collaborations with Sweden and Japan, he gained experience in all major approaches to toroidal confinement (tokamak, spherical tokamak, stellarator and reversed field pinches), and participated in modeling for ITER, the large international tokamak under construction in France, which is expected to produce net fusion power for the first time.

Prof. Volpe will continue his collaboration with the DIII-D national facility in San Diego; will establish a local research program on small university-scale plasma experiments; and will coordinate the development, at Columbia, of innovative plasma diagnostics to be deployed in local and external plasma confinement devices.

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