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"Learn what is to be taken seriously and laugh at the rest." Hermann Hesse, Steppenwolf

Research

Paul earned his Bachelors of Science in Mathematics and Physics from the University of Arizona and his Masters of Science in Physics at the University of Wisconsin, Madison. In December of 2006, he completed his Ph.D. in Physics at the University of Maryland, College Park. He is currently a postdoctoral researcher in the Department of Physics and Astronomy at the University of Delaware .

Magnetic reconnection, nonlinear dynamics, physics of the solar corona, magnetospheric physics, fusion physics, space physics, plasma theory, physics education and outreach.

Magnetic reconnection is a fundamental plasma physics phenomenon involved in the large scale conversion of energy stored in magnetic fields into flow and heat of the surrounding plasma. Applications include solar flares and substorms in the Earth's magnetosphere, among many others.

Below is a link to a talk Paul gave at the AGU 2008 Joint Assembly meeting. It was an SPD Parker Lecture which celebrated the contributions of Eugene Parker in honor of the fiftieth anniversary of his paper predicting a solar wind. This talked covered the early history of the theory of magnetic reconnection, a more recent history through the 20th century, and a look at the questions people are working on in the 21st century. Please contact Paul with any comments or questions.

Paul's research, carried out with Jim Drake and Michael Shay, has focused on the long-standing "Onset Problem" of magnetic reconnection. One must explain why reconnection events observed in Nature, such as solar flares, sawtooth crashes in fusion devices, and magnetospheric substorms, begin explosively. In addition to understanding the trigger mechanism which begins the reconnection process, one must also explain what prevents the trigger from occurring before a substantial buildup of free energy has taken place.

A notable publication shows that magnetic reconnection is bistable: the slow Sweet-Parker and fast Hall reconnection solutions are both accessible for a wide range of collisionalities. The edge of the bistable regime is catastrophic: as the thickness of the dissipation region is decreased, the Sweet-Parker solution abruptly ceases to exist. This provides a potential explanation to the Onset Problem: for a system undergoing Sweet-Parker reconnection, free magnetic energy accumulates. As the dissipation region thins, a critical threshold is passed, where the Sweet-Parker solution disappears and Hall reconnection begins abruptly. The stored magnetic energy is rapidly released during Hall reconnection.

See below for links to the above publication, two "popular" articles about the paper, and three follow up papers describing 1) what causes the dissipation region to become thinner, 2) an extension of the previous work to include a guide field, and 3) how the existence of an intermediate unstable reconnection solution provides evidence that the onset of fast reconnection occurs due to physics locally near the X-line as opposed to at the boundaries.

Another project deals with the scaling and properties of asymmetric magnetic reconnection, that is, reconnection between plasmas of different density and with different magnetic field strengths. Much work has been done on the shock structure, but scaling with ambient system parameters had not been performed. We performed an analytic scaling analysis (in 2D with anti-parallel fields) and found the location of the X-line and stagnation point, showing that the two points are not colocated in general. We verified the results using Resistive MHD simulations. A link to the paper is below.