Plasma control by modification of helicon wave propagation in low magnetic fields

By making use of nonuniform magnetic fields, it is shown experimentally that control of helicon wave propagation can be achieved in a low pressure (0.08 Pa) expanding plasma. The m=1 helicon waves are formed during a direct capacitive to wave mode transition that occurs in a low diverging magnetic field(B₀<3 mT). In this initial configuration, waves are prevented from reaching the downstream region, but slight modifications to the magnetic field allows the axial distance over which waves can propagate to be controlled. By changing the effective propagation distance in this way, significant modification of the density and plasma potential profiles can be achieved, showing that the rf power deposition can be spatially controlled as well. Critical to the modification of the wave propagation behavior is the magnetic field strength (and geometry) near the exit of the plasma source region, which gives electron cyclotron frequencies close to the wave frequency of 13.56 MHz

Detailed plasma potential measurements in a radio-frequency expanding plasma obtained from various electrostatic probes

On-axis plasma potential measurements have been made with an emissive probe in a low pressure (0.044 Pa) rf expanding plasma containing an ion beam. The beam is detected with a retarding field energy analyzer (RFEA), and is seen to disappear at high pressure (0.39 Pa). The emissive probe measurements are in very good agreement with corresponding measurements made with two separate RFEAs, and the results indicate that the floating potential of the strongly emitting probe gives an accurate measure of the plasma potential under the present conditions

Boron nanobelts grown under intensive ion bombardment

High-quality α-tetragonal crystalline boronnanobelts with [001] growth axis were synthesized using a novel method combining e-beam evaporation and plasma ion bombardment techniques. Intensive ion bombardment of the growingboronnanobelts at a high substrate temperature (∼1200°C) was found to be effective in increasing the atomic density, reducing the crystal disorder, and improving the yield of the nanobelts.This work was supported by the Australian Research Council ARC

Terrorism: Local Government Response

Every community in America has the potential to be the target of a terrorist attack. When this attack occurs it is the responsibility of local government agencies to combat the problem. These agencies lack many of the resources needed to successfully deal with these types of attacks. Furthermore, many local governments are under the illusion that the federal government and all of its resources will quickly arrive and assume control of the operation

Master of Science

thesisIgneous apatite is an early magmatic phase that accepts a wide variety of elemental substitutions. These substitutions include porphyry Cu hypogene mineralization elements S and Cu, as well as other potentially mineralization related elements. These characteristics make apatite useful in understanding pre-exsolution concentrations of these elements in melts and, subsequently, useful as porphyry system/intrusive unit fertility indicators. Apatite element substitution concentrations in pre-, syn- and late-mineralization emplaced units of the San Enrique Monolito deposit in the Los Bronces-Río Blanco porphyry district, Central Chile were assessed to evaluate the use of apatite substitutions as porphyry system/intrusive unit fertility indicators. Major, trace and rare earth element (REE) concentrations in apatite grains were determined, sulfur substitution mechanisms and controls were assessed, melt S was calculated using apatite/melt S partition coefficients and apatite S, melt S, and other elemental substitution correlations to mineralization were determined. The ratio of S to Na substitution indicates S in analyzed apatite grains is incorporated by the coupled exchange S6+ + Na+ P5+ + Ca2+ and systematic fluctuations in Cl vs. Mn, Fe and light rare earth elements (LREE) suggest a change in apatite structure associated with concomitant increases in these elements. Neither S exchange nor crystal structure, however, display a preferential control on S uptake. This is interpreted to indicate S concentrations are wholly a function of S availability in melt. Apatite S and melt S are low in premineralization emplaced units, elevated in syn and late-mineralization units and highest in units emplaced contemporaneously with the height of mineralization. Apatite Cu correlates similarly. Apatite Mg was detected only in grains from synmineralization emplaced units, possibly substantiating mafic magma input and underplating as Cu source models for porphyry mineralization. Concentrations of apatite S and melt S above 750 ppm and 200 ppm, respectively, are proposed as fertility indicators. However, because of the cumulative uncertainty associated with melt S calculations, it is proposed that apatite S is a more robust discriminant than melt S. Apatite Cu above 700 ppm and apatite Mg above 300 ppm are also proposed as mineralization potential indicators

Particle-in-cell simulations of ambipolar and nonambipolar diffusion in magnetized plasmas

Using a two-dimensional particle-in-cell simulation, we investigate cross-field diffusion in low-pressure magnetized plasmas both in the presence and absence of conducting axial boundaries. With no axial boundary, the cross-field diffusion is observed to be ambipolar, as expected. However, when axial boundaries are added, the diffusion becomes distinctly nonambipolar. Electrons are prevented from escaping to the transverse walls and are preferentially removed from the discharge along the magnetic field lines, thus allowing quasi-neutrality to be maintained via a short-circuit effect at the axial boundaries

Particle-in-cell simulations of hollow cathode enhanced capacitively coupled radio frequency discharges

A two-dimensional particle-in-cell simulation has been developed to study density enhancement of capacitively coupled rf discharges with multi-slit electrodes. The observed density increase is shown to result from a hollow cathode effect that takes place within the multi-slit electrode configuration, which forms as a result of secondary electron emission due to ion bombardment. By investigating the ionization and power deposition profiles, it is found that rfsheathheating is too weak to sustain the discharge, and that secondary electron acceleration within the sheath is the primary heating mechanism. Due to a capacitive voltage divider formed by the rfsheaths at each electrode, the area ratio of the powered and ground electrodes is observed to have a strong effect on the resulting discharge, and if the ground electrode area is too small, the voltage drop at the powered electrode is too low to sustain a hollow cathodedischarge.The authors gratefully acknowledge financial support from the Lam Research Corporation

Hydrogen contamination in Ge-doped SiO[sub 2] thin films prepared by helicon activated reactive evaporation

Germanium-doped silicon oxidethin films were deposited at low temperature by using an improved helicon plasma assisted reactive evaporation technique. The origins of hydrogen contamination in the film were investigated, and were found to be H incorporation during deposition and postdeposition water absorption. The H incorporation during deposition was avoided by using an effective method to eliminate the residual hydrogen present in the depositionsystem. The microstructure, chemical bonds, chemical etch rate, and optical index of the films were studied as a function of the deposition conditions. Granular microstructures were observed in low-density films, and were found to be the cause of postdeposition water absorption. The granular microstructure was eliminated and the film was densified by increasing the helicon plasma power and substrate bias during deposition. A high-density film was shown to have no postdeposition water absorption and no OH detected by using a Fourier-transform infrared spectrometer

State Funding for Ports: Selected State Summaries and Links to Resources

The maritime industry in the United States, which plays a significant role in the economies of coastal states and the nation as a whole, involves a diverse variety of working waterfronts, ranging from large commercial ports that facilitate heavy industry to small-scale, traditional working waterfronts. Moreover, in many areas of the country, the economic and cultural identities of local communities depend almost exclusively on traditional working waterfronts. Unfortunately, land use and economic policy shocks, such as escalating coastal property values and taxes, increasing demands for non-water-dependent land uses, and complex and time-consuming permitting processes, currently threaten many working waterfronts. Since waterfront land is essentially a non-renewable resource, these pressures are likely to intensify, with more than half the U.S. population (153 million people) living in coastal zones. Additionally, the number of people 65 years and older living in coastal zones is expected to increase by 147% over the next 50 years (these people come to the coast for reasons other than economic reasons). Further compounding this pressure, waterfront infrastructure almost always amounts to a long-term capital investment, which demands stable planning and funding mechanisms. Thus, where state policies fail to make the appropriate financial resources available to waterfront communities, these communities face an uphill battle to remain viable – essentially playing third-fiddle to other ports in the state, ports in other states, and non-water-dependent land uses, such as luxury residential projects