The Fermilab 1990-1991 Fixed Target Pmgmm featured six experiments utilizing liquid hydrogen or liquid deuterium targets as part of their apparatus. Each design was optimized to the criteria of the experiment. resulting in variations of material selection, methods of refrigeradonandsecondary containment. Collecdvely.therargetswererunforatotalof 14,184 hours with an average operational efficiency of 97.6%. The safe and reliable operation of these targets was complemented by an increased degree of documentation and component testing. This operation was also aided by several key upgrades. All the systems were designed and fabricated under a set of written guidelines that blend analytical calculations and empirical guidance drawn from over twenty years of target fabrication experience.
<p>Rayleigh-B&#233;nard convection (RBC) is a fluid phenomenon that has been studied for over a century because of its utility in simplifying very complex physical systems. Many geophysical and astrophysical systems, including planetary core dynamics and components of weather prediction, are modeled by including rotational forcing in classic RBC. Our understanding of these systems is confined by experimental and numerical limits, as well as theoretical assumptions.&#160;</p><p>The role of thermal boundary condition choice on experimental studies of geophysical and astrophysical systems has been often been overlooked, which could account for some lack of agreement between experimental and numerical models as well as the actual flows. The typical thermal boundary conditions prescribed at the top and the bottom of a convection system are fixed temperature conditions, despite few real geophysical systems being bounded with a fixed temperature. A constant heat flux is generally more applicable for real large-scale geophysical systems. However, when this condition is applied in numerical systems, the lack of fixed temperature can cause a temperature drift. In this study, we seek to minimize temperature drifting by applying a fixed temperature condition on one boundary and a fixed thermal flux on the other.</p><p>Experimental boundary conditions are also often assumed to be a fixed temperature. However, the actual condition is determined by the ratio of the height and thermal conductivity of the boundary material to that of the contained fluid, known as the Biot number. The relationship between the Biot number and thermal boundary condition behavior is defined by the Robin, or 'thin-lid', boundary condition such that low Biot number boundaries are essentially fixed thermal flux and high Biot number boundaries are essentially fixed temperature.&#160;</p><p>This study seeks to strengthen the link between numerical and experimental models and geophysical flows by investigating the effects of thermal boundary conditions and their relationship to real-world processes. Both fixed temperature and fixed flux boundary conditions are considered. In addition, the Robin boundary condition is studied at a range of Biot numbers spanning from fixed temperature to fixed flux, allowing intermediate conditions to be investigated. Each system is studied at increasingly rapid rotation rates, corresponding to decreasing Ekman numbers as low as Ek=10<sup>-5</sup> Heat transport is analyzed using the Nusselt number, Nu, and the form of the solution is described by the number of convection rolls and time-dependency. Further investigations will analyze Nu and fluid movement within a system with heterogeneous heat flux condition on the &#160;sidewall boundary conditions, which is useful in the study of planetary core dynamics. The results of this study have implications for improvements in modeling geophysical systems both experimentally and numerically.&#160;</p>
<p>The investigation of planetary cores is of great interest to those seeking to better understand magnetic fields and the life-processes of planets. Like many large-scale systems, planetary cores are unable to be modelled perfectly by numerical simulations or physical experiments. However, it is of constant importance to improve numerical and experimental methods and designs to better replicate full-scale processes. Many previous studies have over-looked the effects of the inhomogeneous insulation from the Earth's mantle on convection in the core. A few numerical studies have taken this effect into consideration for rotating Rayleigh-Benard convection (RBC) in spherical geometries. Experimental models are desirable to further understand the motion of fluid in the center of planets; however, due to physical limits, spherical systems are difficult to recreate experimentally. Therefore, cylindrical geometries are useful to study varied thermal flux on sidewalls both experimentally and numerically. While some studies have numerically and experimentally considered changes in temperature along the sidewall, there has been little consideration for variations in heat flux, which is the more physically appropriate boundary condition.&#160;</p><p><br>The present study seeks to explore rotating RBC in a cylindrical domain with sidewalls inhomogeneously insulated in an experimentally-achievable system. It is experimentally plausible that the material of a cylindrical cell could varying in thickness, and therefore thermal conductivity, or have patches of heating and/or cooling attached to the sidewall to vary the thermal flux on the side boundaries. To imitate this numerically, a sinusoidal pattern of increasing and decreasing heat flux is applied to the sidewall in two cases: one whereby heat flux fluctuates between positive and negative, and another whereby the heat flux is strictly positive. Additionally the mode and amplitude of the wave is considered. The mode will either match the mode of the system with insulating sidewall conditions or have a larger wavelength to better simulate planetary cores. The amplitude is increased as necessary to achieve significant results. For simplicity, the top and bottom boundary conditions are fixed temperature.</p><p><br>Changes in heat transport and temporal behavior are measured with a global Nusselt number, Nu, time series. Additional variables such as mean zonal flow, number and location of convection rolls, and transitions to time-dependence are considered. Results indicate that large-wavelength heat flux on the sidewalls causes two modes to inhabit the system, existing on opposite sides of the cylinder: the mode natural to the homogeneously insulated system exists where heat flux is high and a large-wavelength mode dominates where heat flux is lower. However, the implementation of heat flux along the sidewalls with the same wavelength of the insulated system results in near-time independence as the amplitude increases. These results indicate that variation in heat flux boundary conditions can cause significant changes in rotating RBC behavior. Experimental studies could be used to validate or refute these conclusions. Overall, it is clear that numerical studies of molten planetary cores heterogeneously heated by mantles must take these irregularities into consideration to improve our understanding of core convection.&#160;</p>
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