Research Interests

Dr. Holland’s research concentrates on short scale length, equilibrium structures in magnetized plasmas, i.e. structures in the cross-field direction whose scale length is on the order of or less than an ion gyroradius or less. In recent years, his research has focused on three main problems: 1) the results of nonlinear particle dynamics in the earth’s magnetotial, 2) sheath structures in strongly magnetized plasmas and 3) the Plasma Sheet Boundary Layer-Lobe interface in the earth’s magnetotail.

The rapid magnetic field variation in the center of the magnetotial current sheet results in very complex and sometimes chaotic particle dynamics. In the early 1990’s it was predicted that the dynamics would produce peaks and valleys in the ion distribution function with a separation that scales as the fourth root of the normalized ion energy. This signature was tentatively identified in ISEE-1 data and it was suggested that the locations of the peaks and valleys could be used to determine the current sheet topology using a single satellite. In the intervening years, Dr. Holland has examined a number of aspects of this problem. His original work found that the ion distribution function signature should be robust in the presence of weak to moderate levels of noise and to cross-tail magnetic fields. Following this he examined the self-consistent current sheet structures that result from the fully nonlinear ion dynamics. (In effect this was simply a brute force numerical solution to the zeroth order Vlasov equation.) Most recently Dr. Holland has been systematically going through the Geotail Comprehensive Plasma Instrument (CPI) data to verify the existence the distribution function signature under varying Geomagnetic conditions and to use the signature, combined with magnetometer data, to infer the current sheet topology.

 

In recent years the sheath formed between a magnetized plasma and a material wall has received a great deal of attention. This interest stems primarily from an increased awareness of the importance of the boundary conditions to the global confinement properties of fusion plasmas. While still a graduate student, Dr. Holland developed a self-consistent equilibrium model of the magnetized sheath that is relevant to the diveretor region of tokamaks. More recently, he has been extending the analytical model to apply to a wider range of parameter space and also using the self-consistent sheath structure to calculate ion impact distributions. This information is critical for predicting the sputtering rate of impurities into the plasma. Finally, he is beginning a program to use particle in cell codes to investigate the sheath dynamics under the influence of changes in external parameters (e.g. magnetic field angles, particle density, etc.).

 

The interface between the plasma sheet boundary layer and the lobe in the magnetotail is characterized by rapid variations in the plasma density and temperature as well as the magnetic field strength. The free energy in such a region acts as a source of broad-band electrostatic noise. Working with an undergraduate student, Dr. Holland developed a self-consistent finite beta equilibrium model of this region. In the low beta regime, the results are identical to previous analytic models of the interface. Using their model, they were able to show that the characteristics of the wave generation should remain basically unchanged from the low beta to the high beta regime.

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