James F. Drake

Professor of Physics
University of Maryland, College Park, MD

B. S., M. S. and Ph. D., Physics, University of California, Los Angeles

Professor Drake earned his bachelors degree from UCLA and remained at UCLA to complete his doctorate in theoretical physics in 1975. After completing his doctorate, Professor Drake remained at UCLA for a brief time as a post-doctoral scholar and then moved to the University of Maryland first as a post-doctoral scholar and then as a member of the teaching faculty in the Department of Physics and the Institute for Physical Science and Technology.

Professor Drake has worked on a very broad range of topics in the general area of theoretical plasma physics using both analytical and numerical techniques. His work has applications spanning a variety of physical systems, including the solar corona, the earth's magnetosphere and ionosphere, magnetically confined plasma, and the interaction of intense lasers with plasma. His present focus is on magnetic reconnection with space physics applications and turbulence and transport with applications to the magnetic fusion program. In recognition for his contributions to the field of plasma physics, he was granted fellowship status in the American Physical Society and was awarded a Humboldt Senior Scientist Research Award.

Magnetic Reconnection

Solar flares, storms in the earth's magnetosphere and disruptions in laboratory fusion experiments are examples of large scale explosive events which occur in plasma systems. The magnetic field is the source of free energy driving these phenomena. This magnetic energy can be released in locations where the magnetic field reverses direction. That is, the magnetic field can self-annihilate in these regions and transfer its energy to plasma flows and intense, high energy beams. A major scientific challenge has been to explain the short time scales of this energy release. It is well established that the magnetic energy is released by magnetic reconnection, in which magnetic field lines in opposing directions cross link, forming a topological x-line. The topological change in the magnetic field required to form the x-line requires a breakdown in the ideal "frozen-in" flux condition, which occurs at small scales. As a result, magnetic reconnection occurs in narrow boundary layers. This topic is considered to be one of the two or three most important topics in plasma physics over the past thirty years because it occurs in so many varied environments and because the dependence of a large-scale, explosive phenomenon on the kinetic behavior at small scale has intrinsic interest.

Key discoveries in magnetic reconnection made by Dr. Drake and his colleagues center around the role of whistler waves in driving and controlling magnetic reconnection. Traditionally it was believed that the Alfven wave played the key role in driving reconnection. At small scales, however, electron and ion motion decouple and the dynamics is controlled by whistler waves. The whistler waves fundamentally alter the reconnection process, causing the release rate of magnetic energy to be insensitive to the mechanism which breaks the frozen-in condition. The figure on the right shows the results of a computer simulation of magnetic reconnection. From top to bottom are the magnetic field lines, the plasma flows, and the ion and electron currents. You can watch a computer generated movie of fast collisionless reconnection. The black lines are magnetic field lines, which move toward each other and reconnect. The slingshot-like behavior after reconnecting enables the magnetic field to release its energy.

Key papers dealing with collisionless magnetic reconnection and associated particle acceleration are:

Some recent news articles which have appeared discussing fast magnetic reconnection:

Plasma Turbulence, Transport and Nonlinear Instability

The transport of plasma across magnetic fields plays a critical role in most plasma systems, including boundary layers and shocks in space and in laboratory magnetic fusion experiments. For example, energy confined in laboratory fusion experiments leaks across the magnetic field much faster than can be explained from predictions based on classical Coulomb collisions. The free energy associated with the large gradients of plasma pressure drives very small scale vortices which cause the plasma wander across the magnetic field to the cold walls of the container. Basic questions such as the explicit mechanism which drives these vortices, what controls the level of fluctuations and how the resulting plasma transport scales with the plasma parameters remain poorly understood. Dr. Drake and his colleagues at Maryland have developed a powerful 3-D numerical model for exploring the nonlinear development of turbulence and transport in magnetized plasma. This tool has been used to explore a range of fundamental issues related to the nonlinear dynamics of plasma turbulence and to answer very practical questions such as the scaling of energy and particle transport.

A major surprise in this work was the discovery that linear stability is not always an accurate indicator of the behavior of a system. The classical approach for studying the dynamics of a system is to first assume that the system is in equilibrium and explore the stability around the equilibrium using linear perturbation theory. The assumption is that if linear disturbances are stable, the system will remain in a quiescent state. This whole approach has been questioned in the case of pipe flow, where turbulence develops at Reynolds numbers well below the predictions of simple linear stability theory, but has remained largely unquestioned in other areas. In inhomogeneous magnetically confined plasma transport can be dominated by a nonlinear instability which has no counterpart in linear perturbation theory. The linear properties of the system are essentially irrelevant. A simple picture of the nature of the nonlinear instability was formulated and a truncated set of equations have been derived to produce the behavior, which was first observed in a complex 3-D simulation of plasma turbulence. This work has broad implications for understanding the dynamics of complex systems. Recent papers dealing with turbulence and transport are: