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Planetary surfaces exposed to the solar wind and high energy solar radiation develop a charge due to photoemission, collection of solar wind electrons and ions, and secondary electron emission. Dust particles on the surface can be lifted off the surface and transported by the plasma sheath electric field. Observations of a lunar “horizon glow” by several Surveyor spacecraft on the lunar surface in the 1960s and detections of dust particle impacts by the Apollo 17 Lunar Ejecta and Meteoroid Experiment (LEAM) have been explained as the result of micron-sized charged particles lifting off the surface. The NEAR/Shoemaker spacecraft observed unusual deposits of fine material in some craters on the asteroid Eros that may be the result of electrostatic transport of dust. I will give an overview of observations from the Moon and Eros and numerical simulations of the process of charged dust transport in a dayside photoelectron sheath.

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The interaction of the solar wind with the Earth's magnetic field creates several large sheets of electric current, including the ~10 MA tail current sheet which flows above geosynchronous orbit. A variety of nonlinear plasma processes occur within this sheet and its dynamics control much of the Earth's magnetosphere. Understanding its equilibrium configuration is thus an important step in resolving broader issues including current-driven instabilities, reconnection and the overall dynamics of the magnetosphere. Despite the large physical size, the equilibrium structure is frequently too thin to be describable within the framework of magnetohydrodynamics; consequently, realistic models must be built with Vlasov-Maxwell theory. Detailed observations of the tail current sheet are available from many satellites, most notably a set of 4 European Space Agency satellites known as Cluster. However, by comparing Cluster observations to available current sheet models, it becomes clear that the existing models are generally insufficient for describing the configuration. By using the observations as a guide, I will discuss the generalization of an existing class of models to create an exact semi-analytic Vlasov model that can better represent the real tail current sheet.

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This seminar will focus on the operating principles and capabilities of ion thrusters. Processes applied to generate energetic electrons and thence ions, to extract and accelerate the ions, and to neutralize the resulting ion beam will be discussed. The reasons why these thrusters are being used so successfully for stationkeeping and orbit-raising missions on Earth satellites and why they were so successful on the Deep Space One mission will be mentioned. Numerical modeling results that describe the ion extraction and acceleration process will be compared to corresponding experimental results obtained using small arrays of ion extraction aperture pairs (gridlet studies). The great potential of electric thrusters for future advanced satellite and exploration missions including NASA’s DAWN mission will be mentioned.

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Beam-target fusion is not of economic interest, as the beam drag power exceeds the fusion yield. This picture changes if one imagines using the heat produced by beam drag as a low entropy source (because of the high plasma temperature) rather than exhausting it. This elementary thermodynamics is fine, but the challenge is in the (conceptual) engineering. How to arrange a confined plasma to form a high efficiency heat engine and how to use the mechanical energy to form a beam? Known electrostatic fusion concepts are extended to "conventional" magnetically confined quasi-neutral plasmas. Rapidly (supersonic) rotating plasmas are particularly useful for this. The rotation forms a mechanical energy reservoir and the cross field electrical potentials are useful for particle acceleration.

In this talk, two new physics ideas are developed and applied to this problem. First idea: electrostatic wells are replaced by centrifugal wells and non-neutral plasma replaced by quasi-neutral plasma. Previously known physics are applied, leading to many arrangements which form a high-efficiency (<90%) heat engine. Simplest of all is the Pastukov problem, in which a single well confines a low-collisionality nearly thermal plasma. It is shown that a proper arrangement of magnetic field (essentially the open field of a field-reversed configuration – FRC) can make this into a heat engine, so that plasma heat becomes rotation. The energy cycle is completed by converting rotation to beam energy. It is shown how to use the high electrical potentials induced by rotation to electrostatically accelerate a beam into the confined plasma.

Second idea: plasma rotation can produce plasma waves from a static magnetic perturbation, using nothing more than the Doppler effect. These waves can also be used to produce a desired beam by resonant absorption. Another use for such waves is to drive currents. As already demonstrated experimentally, such currents can form a FRC.

All of this leads to lowering the fusion threshold. In particular, required temperatures are greatly reduced, leading to very small, very high-power density systems. The non-thermal fusion also means that aneutronic fuel cycles can be used. Some examples are given. Finally, a small experiment to test these physics is being planned and some details of this design are given.

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Metamaterials are artificial periodic structures made of small elements and designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be described by a permittivity and permeability, just like natural materials. When the permittivity and permeability are simultaneously negative in some frequency range, the metamaterial is called double negative or left-handed and has some unusual properties. Left-handed metamaterials (LHM) have potential applications in active and passive devices at millimeter waves and at much higher frequencies. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves can be produced in a LHM-loaded waveguide without corrugations. The dispersion relation of a LHM-loaded waveguide has several interesting frequency bands which are described. Left-handed structures can be employed at X-band accelerators to suppress wakefields.

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Plasma sputtering can greatly reduce the size of charged dust grains orbiting within the magnetosphere of Saturn in only a few decades.With mass and charge varying in time, the resulting equations of motion are non-hamiltonian. Except for the small influence of solar radiation pressure, this systems is axisymmetric and the question arises as to the existence of global invariants in the absence of a hamiltonian. For larger grains, where gravity dominates we show that a formal hamiltonian may be constructed by treating the velocities as canonical momenta. For smaller grains, where the planetary magnetic field dominates, a hamiltonian description is apparently not possible. Nevertheless, an exact invariant is derivable from the axisymmetric equations of motion. Implications for the history and structure of Saturn’s E ring and for observations by the Cassini orbiter CDA and UVIS experiments will be discussed.

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Current mechanisms of coronal mass ejection (CME) initiation tend to rely on ad hoc assumptions to energize coronal magnetic fields to erupt. Most notably, artifi cial shearing of coronal magnetic arcades has been employed for nearly three decades to model fl ares and CMEs while no self-consistent explanation for the shearing motions was known. This talk will focus on the recent discovery that such shearing motions are driven by the Lorentz force that naturally arises when bipolar magnetic fields emerge from the photosphere into the corona. These spontaneous shearing motions will be shown to produce eruptions in a fully self-consistent manner in both magnetic arcades and flux ropes. The shearing motions transport axial flux and energy from the submerged portion of the field to the expanding portion, strongly coupling the solar interior to the corona. This physical process is very robust for explaining the highly sheared state of the magnetic field associated with prominences, and why these magnetic fields erupt in flares and CMEs.

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Spontaneously arising magnetic fields occur widely throughout the universe. Attempts to explain them go back at least to Gauss in 1838 and define the "magnetic dynamo problem." In the context of magnetohydrodynamics (MHD), it is easy to see that some of the possible motions of an electrically-conducting fluid are capable of amplifying arbitrarily small magnetic fields. If the amplification continues, the magnetic fields B and their associated electric currents J become large enough that the Lorentz force JxB ceases to be negligible and begins to participate nonlinearly in the mechanical motion of the fluid, which sometimes may be turbulent. The difficulty lies in making the results quantitative and in accountng for the kinds of magnetic fields (planetary, solar, laboratory, or remotely astrophysical) that are created and observed. We have been doing numerical MHD computations motivated jointly by recent laboratory experiments on liquid sodium (e.g., [1,2]) and the need to account for magnetic fields generated inside spheres [3] in planetary models. An important number is the ratio of fluid viscosity to resistivity (in dimensionless units, the "magnetic Prantdl number"); it has much to say about the ease or difficulty of exciting dynamo processes. The subject will be reviewed at an elementary level, and then samples of our recent computations discussed.

[1] A. Gailitis et al, Phys. Rev. Lett. 86, 003024 (2001).
[2] P.D. Mininni and D.C. Montgomery, Phys. Rev. E72, 056320 (2005).
[3] P.D. Mininni and D.C. Montgomery, "Magnetohydrodynamic activity inside a sphere," arXiv:physics/0602147 (submitted to Phys. Fluids, 2006).

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We investigate the effect of mass loss on the invariants of systems having translational or rotational symmetry. These systems are nonhamiltonian in the physical momenta but, in the case of non-velocity-dependent potentials can be made formally hamiltonian by treating the velocities as canonical momenta. Applying Noether's theorem to the formal Hamiltonian then yields global invariants corresponding to its symmetries. For velocity-dependent potentials such as occur for motion in magnetic fields, an exact invariant is constructed from the (nonhamiltonian) vector field. For adiabatic orbits the motion is thereby reduced from 3D to a 2D manifold with time-dependent effective potential parametrized by the conserved momentum. The results are applied to single particle motion in an axisymmetric gravitational field, the time-dependent Kepler problem, and charged particle motion in linear and axisymmetric magnetic fields. Finally, we indicate how the results might be combined to describe the motion of charged dust grains about Saturn.

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Observations from auroral satellite missions have shown for decades that electron and ion distributions in the auroral region are consistent with being accelerated through magnetic field aligned electric fields (so called parallel electric fields). More recently, FAST (an auroral spacecraft), has directly measured parallel electric fields. However, In a collisionless plasma, there is no generally accepted theoretical description of how parallel electric fields are self-consistently supported.

In this talk, I will show that parallel electric fields can be supported by double layers (DL). I will then show how we solve for such a double layer using methods similar to Bernstein, Green and Kruskal [1957] (the so called BGK method). The distribution functions that we use to construct the DL are modeled from FAST data. Finally, to test whether such a DL is stable, I have initialized a Vlasov simulation with a typical auroral cavity plasma, and have included a double layer to see how it evolves. I will briefly discuss the Vlasov algorithm for evolving distribution functions. One of the new features of the simulation is that we have included two ion species (H+ and O+) in addition to electrons. As a result of having two ion species, I will show how ion phase space holes and other non-linear structures, which are often seen with FAST, form in the simulation.

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