Optimization of Outer Poloidal Field (PF) Coil Configurations for Inductive PF Coil-only Plasma Start-up on Spherical Tori

The elimination of in-board ohmic heating solenoid is required for the spherical torus (ST) to function as an attractive fusion power plant. An in-board ohmic solenoid, along with the shielding needed for its insulation, increases the size and, hence, the cost of the plant. Here, we investigate using static as well as dynamic codes in ST geometries a solenoid-free start-up concept utilizing a set of out-board poloidal field coils. By using the static code, an optimization of coil positions as well as coil currents was performed to demonstrate that it is indeed possible to create a high quality multi-pole field null region while retaining significant flux (volt-seconds) needed for the subsequent current ramp-up. With the dynamic code that includes the effect of vacuum vessel eddy currents, we then showed that it is possible to maintain a large size field null region for several milliseconds in which sufficient ionization avalanche can develop in the applied toroidal electric field. Under the magnetic geometry typical of a next generation spherical torus experiment, it is shown that the well-known plasma breakdown conditions for conventional ohmic solenoid start-up of E(sub)TB(sub)T/B(sub)P {approx} (0.1-1) kV/m with V(sub)loop {approx} 6 V can be readily met while retaining significant volt-seconds {approx} 4 V-S sufficient to generate multi-MA plasma current in STs

Formation of Mesoporous Materials from Silica Dissolved in Various NaOH Concentrations: Effect of pH and Ionic Strength

We describe the effects of NaOH/SiO2 ratio and pH on the formation of mesoporous materials, which was synthesized via an alkali-metal hydroxide fusion method, from amorphous silica dissolved in NaOH. Physical properties (e.g., specific surface area, pore volume, and pore size) of mesoporous materials synthesized at different conditions (i.e., pH, NaOH/SiO2 ratio) were evaluated through X-ray diffraction, nitrogen adsorption-desorption, and transmission electron microscope analyses. The results showed that, at the NaOH/SiO2 ratios of 0.5, 1, and 2, gels were successfully synthesized while no product was formed at the NaOH/SiO2 ratios greater than 2. Additionally, mesoporous materials were found to be formed at both pH 10 and 11 while they were unstable under more alkaline conditions. The adsorption/desorption isotherm results for the mesoporous materials synthesized at around pH 11 and with NaOH/SiO2 ratios of 0.5–0.8 showed a hysteresis loop characteristic of the bottle-neck pore shape. Furthermore, mesoporous materials with good physical properties were synthesized from all gels at pH 10 regardless of sodium concentration

Pore Characteristics and Hydrothermal Stability of Mesoporous Silica: Role of Oleic Acid

Silicate mesoporous materials were synthesized with nonionic surfactant and their surfaces were modified by oleic acid adsorption. Infrared spectrometer, nitrogen adsorption-desorption isotherm, scanning electron microscopy, and thermogravimetric analyses were used to investigate the structure of oleic acid modified mesoporous material. The effects of heat treatment at various temperatures on oleic acid modified materials were also studied. Oleic acids on silica surfaces were found to be bonded chemically and/or physically and be capable of enduring up to 180°C. The adsorbed oleic acid improved the hydrothermal stability of mesoporous silica and assisted mesopore structure to grow more in hydrothermal treatment process by preventing the approach of water

Use of Linear Viscoelastic Theory to Predict Resilient Behavior of Unbound Granular Materials

This paper presents a methodology to estimate the stress-strain relationship of an unbound aggregate base using linear viscoelastic theory. Current Mechanistic-Empirical (ME) pavement design procedure adopts the resilient modulus concept to explain the behavior of granular materials for flexible pavement design. The resilient modulus is a stress dependent material property of granular materials that is different from strength. Although California Bearing Ratio (CBR) test results (i.e., stress and strain) can be used to estimate the strength of a granular material, it is not possible to estimate the resilient modulus directly. Therefore, it is necessary to estimate stress along with strain changes. The convolution integral enables the stress to be estimated from the given strain changes only if the relaxation modulus is measured. Aggregate specimens prepared from two different sources in Georgia were subjected to the relaxation modulus test. From the test data, the time-dependent stress due to a known strain rate was computed as a convolution integral of the strain. The computed stress-strain relationship was compared with that from the resilient modulus (M R ) test. The results indicate that the stress-strain relationships from the M R test and the convolution integral are similar with nearly the same slopes when horizontal stress is assumed to be approximately 45% of vertical stress. This observation supports the use of the proposed methodology by state highway agencies to validate the M R test results for quality control and quality assurance of aggregate base material selection for pavement design and construction

Development of thin-foil based infrared bolometer system in KSTAR

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Radiation measurement in plasma disruption by thin-foil infrared bolometer

A thin-foil infrared bolometer has been developed to measure the plasma radiation quantitatively during plasma disruptions in the KSTAR tokamak. We present analytic solutions of a 0D heat transfer model, which enable the estimation of the plasma radiation from the bolometer signal. The analytical solutions for the linear response regime give practical ways by which the radiation power and energy can be estimated from the cooling time scale of the bolometer signal. A useful way of evaluating the linear response of the system is also introduced. The analysis is complemented by 2D heat transfer simulations. The bolometer signals from the shattered pellet injection experiments in the 2020 KSTAR campaign are analyzed and interpreted according to the heat transfer models.11Nsciescopu