Flow Dynamics And Plasma Heating Of Spheromaks In SSX

We report several new experimental results related to flow dynamics and heating from single dipole-trapped spheromaks and spheromak merging studies at SSX. Single spheromaks (stabilized with a pair of external coils, see Brown, Phys. Plasmas 13 102503 (2006)) and merged FRC-like configurations (see Brown, Phys. Plasmas 13, 056503 (2006)) are trapped in our prolate (R = 0.2 m, L = 0.6 m) copper flux conserver. Local spheromak flow is studied with two Mach probes (r(1) = rho(i) ) calibrated by time-of-flight with a fast set of magnetic probes at the edge of the device. Both Mach probes feature six ion collectors housed in a boron nitride sheath. The larger Mach probe will ultimately be used in the MST reversed field pinch. Line averaged flow is measured by ion Doppler spectroscopy (IDS) at the midplane. The SSX IDS instrument measures with 1 mu s or better time resolution the width and Doppler shift of the C-III impurity (H plasma) 229.7 nm line to determine the temperature and line-averaged flow velocity (see Cothran, RSI 77, 063504 (2006)). We find axial flows up to 100 km/s during formation of the dipole trapped spheromak. Flow returns at the wall to form a large vortex. Recent high-resolution IDS velocity measurements during spheromak merging show bi-directional outflow jets at +/- 40 km/s (nearly the Alfven speed). We also measure T-i \u3e= 80 eV and T-e \u3e= 20 eV during spheromak merging events after all plasma facing surfaces are cleaned with helium glow discharge conditioning. Transient electron heating is inferred from bursts on a four-channel soft x-ray array. The spheromaks are also characterized by a suite of magnetic probe arrays for magnetic structure B(r,t), and interferometry for n(e) . Finally, we are designing a new oblate, trapezoidal flux conserver for FRC studies. Equilibrium and dynamical simulations suggest that a tilt-stable, oblate FRC can be formed by spheromak merging in the new flux conserver

Relationship of \u3cem\u3eSphaeroma quoianum\u3c/em\u3e to Sediment Characteristics and Invertebrate Community

Many important wetland functions are tied to sediment dynamics, which are influenced by infaunal invertebrate communities. These communities are sensitive to changes in sediment structure and to colonization by non-native species. In a southern California salt marsh, the non-native isopod Sphaeroma quoianum has created dense networks of burrows within the marsh banks. Since this isopod increases erosion in many areas and can change local invertebrate communities, its possible contribution to habitat loss in this already-scarce southern California ecosystem is an important issue. To determine the relationship of S. quoianum to invertebrate community and sediment characteristics, three burrowed transects and one unburrowed transect were surveyed and sampled for invertebrate and sediment cores. This study tested the association between burrows and grain size distribution, sediment carbon content, respiration rates, and invertebrate community composition. Sphaeroma quoianum burrows were correlated with altered invertebrate community composition, decreased carbon content, and steep marsh bluffs. These results highlight the potential susceptibility of salt marsh habitat with steep edges to invasion by non-native species. These results also suggest that S. quoianum invasion of salt marsh habitats can alter native communities and ecosystem functions; thus, incipient invasions should be of concern to managers and ecologists alike

Comparative analysis of energy consumption trends in cohousing and alternate housing arrangements

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.Includes bibliographical references (p. 91-92).The sizes of both single-family and multifamily homes have grown steadily in the United States over the last fifty years. During this time, despite more efficient production processes, energy consumption in the country also rose. The many concerns associated with increased energy consumption include hastening depletion of fossil fuel resources, increased dependence on foreign resources for fuel, environmental concerns related to fossil fuel emissions, and ensuring all people have access to economic energy sources. Awareness of the necessity to engage in more sustainable practices (environmentally, economically, and socially) has existed at least since the 1960s. The United Nations formalized these concerns in the 1987 publication, "Our Common Future" in which they defined and popularized the term "sustainable development." Despite this awareness and the continuing efforts of governmental and non-governmental agencies to reduce the impact of energy consumption, the rate of consumption has continued to rise and the rate of growth of energy consumption has only seen marginal improvements in the United States (and has risen dramatically in some developing countries such as China and India).(cont.) One way to reduce the rate of consumption or slow the rate of growth is to reduce the impact of the United States housing market through demand management techniques and energy efficient construction. Cohousing offers one opportunity to accomplish that goal. This thesis outlines the background information related to U.S. energy consumption and housing trends, the relative impact of energy consumption in cohousing, and the challenges of implementing cohousing on a large enough scale to make an impact in nation-wide consumption trends.by Jason R. Brown.S.M