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Merlino, Robert L.

Publications and source records attributed to Merlino, Robert L..

Collaborative Research: Advancing the Physics of Magnetized Dusty Plasmas (Final Scientific /Technical Report)

A plasma is a gas of charged particles – electrons and positive ions in roughly equal concentrations. Plasmas are formed by stripping electrons from neutral atoms and molecules. It is believed that the plasma state of matter comprises over 99% of the universe. Often the plasma coexists with small (1/1000 of a millimeter) dust particles. Some of the plasma particles collect on the dust grains which cause it to be electrically charged, and so become an integral part of the plasma, forming what is called a “dusty plasma”. The large objects in the universe (planets, asteroids, comets, stars) are formed by combining dust grains into larger and larger objects, eventually held together by their self-gravitational attraction. Thus, an understanding of the processes that control the structure and evolution of the universe, requires that we understand the behavior of dusty plasmas. These plasmas also often are embedded in magnetic fields which has a strong influence on their structure and behavior. Thus, developing an understanding of dusty plasmas in magnetic fields, so-called magnetized dusty plasmas, is also essential. In addition to the dusty plasmas occurring in nature, dusty plasmas play an important role in many plasma-based technologies, such as the production of semiconductor devices, and in the next generation of clean-and-green-energy producing devices based on nuclear fusion. The purpose of the work performed with funding provided in this grant by the United States Department of Energy was to produce and investigate the physics of magnetized dusty plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Advancing the Physics of Magnetized Dusty Plasmas (Collaborative Research Final Report)

Dusty (or complex) plasmas are four-component systems consisting of the usual plasma constituents of electrons, ions, and neutral atoms with the addition of a third charged component - nanometer to micrometer sized solid particulates; i.e., "dust". The study of magnetized dusty plasmas is grounded in important questions that are relevant to space, astrophysical, and also technological plasmas and therefore have the potential to make a societal impact. The formation and control of nanometer-sized particles in industrial plasma processes is currently being exploited as a technique to induce the formation of nanocrystals on material surfaces. For example, when combined with magnetron sources, these are important processes that could lead to improved techniques for customizing material synthesis. The interaction between the edge plasma and walls of magnetic confinement fusion devices is a source of particulate material that can be transported throughout the plasma with potentially detrimental effects on plasma performance. Understanding the formation, transport, and destruction of these "dust" particles is of critical importance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Ion-beam focusing in a double-plasma device

The authors studied the propagation of a low-energy charge-neutralized ion beam injected into the target region of a long double-plasma device. A magnetic field of up to about 180 G may be applied along the axis of the device. As a result of charge exchange collisions, the ion beam is attenuated as it propagates into the target region. However, under certain conditions of magnetic field strength and neutral gas pressure, the authors have observed a `reemergence' of the beam on axis far downstream in the target. This reemergence of the ion beam is attributed to a focusing of the ions by a self-consistently produced radial ambipolar electric field. The effect may be expected to occur in other types of plasma devices as well, whenever a sufficiently large radially inward electric field is present.

Johnson, James C.↗

Mass spectrometer for measurements of relative ion concentrations in plasmas

A mass spectrometer which can be used to measure relative ion concentrations in a multiion component plasma has been designed for use in a strong (1-4-kG) uniform magnetic field. The spectrometer features an acceleration region which accelerates thermal ions through a series of three tantalum electrodes at a 30 deg angle to the B field, and a collection region in which ions are selectively collected, depending on the size of their gyroradii, by a cylindrical collector. Relative ion concentrations are determined from measurements of the collector current as a function of accelerating voltage. Results obtained using this instrument in a Q-machine device operated with a two-ion (Cs+/K+) component plasma are presented.

Suszcynsky, David M.↗

Electrostatic ion-cyclotron waves in a two-ion component plasma

The excitation of electrostatic ion cyclotron (EIC) waves is studied in a single-ended Q machine in a two-ion component plasma (Ca+ and K+). Over a large range of relative concentrations of Cs+ and K+ ions, two modes are excited with frequencies greater than the respective cyclotron frequencies of the ions. The results are discussed in terms of a fluid theory of electrostatic ion cyclotron waves in a two-ion component plasma.

Suszcynsky, David M.↗

Anode-type double layers in a nonuniform magnetic field

The properties of strong, magnetized, three-dimensional double layers are studied. The double layers are produced by drawing a discharge to a large anode plate located in the diverging magnetic field region of a cylindrical argon discharge. If the anode voltage is sufficiently high, the electrons that are accelerated through the anode sheath may become sufficiently energetic to ionize the background neutral gas and transform the anode sheath into a strong double layer. The resulting conical-shaped structures, which extend outward from the plate, have parallel, oblique, and perpendicular electric field components with respect to the magnetic field. The axial extent of these structures depends on the plate bias voltage, neutral gas pressure, and the magnetic field. At neutral gas pressures of a few millitorr, the double-layer structures are visually apparent because of the enhanced light emission from neutrals excited by the energetic electrons. Color photographs of some of these structures are shown. The scaling of the width of these double layers with electric field components perpendicular to B is also investigated.

Cartier, Steven L.↗