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Rice, J.

Publications and source records attributed to Rice, J..

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Micron-sized spinel crystals in high level waste glass compositions: Determination of crystal size and crystal fraction

The compositions utilized for immobilization of nuclear waste are controlled using glass property models to avoid the deleterious effects of crystallization in the high-level waste (HLW) vitrification melters. The type and size of the crystals that precipitate during melter operations (typically at 1150 °C) and idling (~ 1000 °C) are significantly impacted by glass composition and thermal history. This study was conducted to measure the impact of melt composition and heat treatment temperature on crystal size and fraction. A matrix of 31 multi-component glasses canvasing the expected Hanford HLW compositional space was developed and the glasses fabricated and heat treated at 850 = T = 950°C. The crystal filling fraction values, as determined by X-ray diffraction, varied from 0.2 to 41.0 wt%. Spinel filling fraction values ranged from 0.0 to 13.8 wt%. One glass of the matrix did not precipitate spinel and contained 0.2 wt% RuO 2 , which was assumed to be undissolved from the melting process. All compositions contained crystals in the as-quenched glass. All of the spinel based crystals present in the glasses were less than 10 µm in diameter, as determined by scanning electron microscopy. Composition and temperature dependent models were generated using the resulting data and the best model fit was obtained by only considering spinel filling fractions (R 2 = 0.83). Two glasses were unable to be characterized due to an inability to process the glass under the conditions of this study. Those glasses were utilized to give insight into a potential multi-component constraint to aid in future statistical composition designs.

Lonergan, C. E.↗
DOE OSTI2018

ICRF mode conversion in three-ion species heating experiment and in flow drive experiment on the Alcator C-Mod tokamak

In recent three-ion species (majority D and H plus a trace level of 3He) ICRF heating experiments on Alcator C-Mod, double mode conversion on both sides of the 3He cyclotron resonance has been observed using the phase contrast imaging (PCI) system. The MC locations are used to estimate the species concentrations in the plasma. Simulation using TORIC shows that with the 3He level <1%, most RF power is absorbed by the 3He ions and the process can generate energetic 3He ions. In mode conversion (MC) flow drive experiment in D(3He) plasma at 8 T, MC waves were also monitored by PCI. The MC ion cyclotron wave (ICW) amplitude and wavenumber kR have been found to correlate with the flow drive force. The MC efficiency, wave-number k of the MC ICW and their dependence on plasma parameters like Te0 have been studied. Based on the experimental observation and numerical study of the dispersion solutions, a hypothesis of the flow drive mechanism has been proposed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Evaluating penalized logistic regression models to predict Heat-Related Electric grid stress days

Understanding the conditions associated with stress on the electricity grid is important in the development of contingency plans for maintaining reliability during periods when the grid is stressed. In this paper, heat-related grid stress and the relationship with weather conditions is examined using data from the eastern United States. Penalized logistic regression models were developed and applied to predict stress on the electric grid using weather data. The inclusion of other weather variables, such as precipitation, in addition to temperature improved model performance. Several candidate models and datasets were examined. A penalized logistic regression model fit at the operation-zone level was found to provide predictive value and interpretability. Additionally, the importance of different weather variables observed at different time scales were examined. Maximum temperature and precipitation were identified as important across all zones while the importance of other weather variables was zone specific. The methods presented in this work are extensible to other regions and can be used to aid in planning and development of the electrical grid.

Bramer, L. M.↗
DOE OSTI2016

Experimental and modeling uncertainties in the validation of lower hybrid current drive

Our work discusses sources of uncertainty in the validation of lower hybrid wave current drive simulations against experiments, by evolving self-consistently the magnetic equilibrium and the heating and current drive profiles, calculated with a combined toroidal ray tracing code and 3D Fokker–Planck solver. The simulations indicate a complex interplay of elements, where uncertainties in the input plasma parameters, in the models and in the transport solver combine and compensate each other, at times. It is concluded that ray-tracing calculations should include a realistic representation of the density and temperature in the region between the confined plasma and the wall, which is especially important in regimes where the LH waves are weakly damped and undergo multiple reflections from the plasma boundary. Uncertainties introduced in the processing of diagnostic data as well as uncertainties introduced by model approximations are assessed. We show that, by comparing the evolution of the plasma parameters in self-consistent simulations with available data, inconsistencies can be identified and limitations in the models or in the experimental data assessed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (s{sup ^}) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s{sup ^}. Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s{sup ^} discharges and that the value of s{sup ^}{sub crit} is consistent with the experimental results s{sup ^}{sub crit}{sup exp}≈0.2∼0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s{sup ^} and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s{sup ^}.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

ADX: a high field, high power density, advanced divertor and RF tokamak

The MIT Plasma Science and Fusion Center and collaborators are proposing a high-performance Advanced Divertor and RF tokamak eXperiment (ADX) – a tokamak specifically designed to address critical gaps in the world fusion research program on the pathway to next step devices: fusion nuclear science facility (FNSF), fusion pilot plant (FPP), and/or demonstration power plant (DEMO). This high field (≥ 6.5 tesla, 1.5 MA), high power density facility (P/S ~ 1.5 MW/m2) will test innovative divertor ideas, including an ‘X-point target divertor’ concept, at the required performance parameters – reactor-level boundary plasma pressures, magnetic field strengths and parallel heat flux densities entering into the divertor region – while simultaneously producing high performance core plasma conditions that are prototypical of a reactor: equilibrated electrons and ions, regimes with low or no torque, and no fueling from external heating and current drive systems. Equally important, the experimental platform will test innovative concepts for lower hybrid current drive (LHCD) and ion-cyclotron range of frequency (ICRF) actuators with the unprecedented ability to deploy launch structures both on the lowmagnetic- field side and the high-magnetic-field side – the latter being a location where energetic plasma-material interactions can be controlled and favorable RF wave physics leads to efficient current drive, current profile control, heating and flow drive. This triple combination – advanced divertors, advanced RF actuators, reactor-prototypical core plasma conditions – will enable ADX to explore enhanced core confinement physics, such as made possible by reversed central shear, using only the types of external drive systems that are considered viable for a fusion power plant. Such an integrated demonstration of high-performance core-divertor operation with steady state sustainment would pave the way toward an attractive pilot plant, as envisioned in the ARC concept (Affordable, Robust, Compact) [B. N. Sorbom, et al., submitted to Fusion Engineering Design, 2014] that makes use of high-temperature superconductor technology – a high-field (9.25 tesla) tokamak the size of the Joint European Torus that produces 270 MW of net electricity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Correlation ECE diagnostic in Alcator C-Mod

Correlation ECE (CECE) is a diagnostic technique that allows measurement of small amplitude electron temperature, Te, fluctuations through standard cross-correlation analysis methods. In Alcator C-Mod, a new CECE diagnostic has been installed[Sung RSI 2012], and interesting phenomena have been observed in various plasma conditions. We find that local Te fluctuations near the edge (ρ ~ 0:8) decrease across the linearto- saturated ohmic confinement transition, with fluctuations decreasing with increasing plasma density[Sung NF 2013], which occurs simultaneously with rotation reversals[Rice NF 2011]. Te fluctuations are also reduced across core rotation reversals with an increase of plasma density in RF heated L-mode plasmas, which implies that the same physics related to the reduction of Te fluctuations may be applied to both ohmic and RF heated L-mode plasmas. In I-mode plasmas, we observe the reduction of core Te fluctuations, which indicates changes of turbulence occur not only in the pedestal region but also in the core across the L/I transition[White NF 2014]. The present CECE diagnostic system in C-Mod and these experimental results are described in this paper.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2011

Conducting Planetary Field Geology on EVA: Lessons from the 2010 DRATS Geologist Crewmembers

In order to prepare for the next phase of planetary surface exploration, the Desert Research and Technology Studies (DRATS) field program seeks to test the next generation of technology needed to explore other surfaces. The 2010 DRATS 14-day field campaign focused on the simultaneous operation of two habitatable rovers, or Space Exploration Vehicles (SEVs). Each rover was crewed by one astronaut/commander and one geologist, with a change in crews on day seven of the mission. This shift change allowed for eight crew members to test the DRATS technology and operational protocols [1,2]. The insights presented in this abstract represent the crew s thoughts on lessons learned from this field season, as well as potential future testing concepts.

Young, Kelsey E.↗
NASA NTRS2011

Lessons Learned for Geologic Data Collection and Sampling: Insights from the Desert RATS 2010 Geologist Crewmembers

Since 1997, Desert Research and Technology Studies (D-RATS) has conducted hardware and operations tests in the Arizona desert that advance human and robotic planetary exploration capabilities. D-RATS 2010 (8/31-9/13) simulated geologic traverses through a terrain of cinder cones, lava flows, and underlying sedimentary units using a pair of crewed rovers and extravehicular activities (EVAs) for geologic fieldwork. There were two sets of crews, each consisting of an engineer/commander and an experienced field geologist drawn from the academic community. A major objective of D-RATS was to examine the functions of a science support team, the roles of geologist crewmembers, and protocols, tools, and technologies needed for effective data collection and sample documentation. Solutions to these problems must consider how terrestrial field geology must be adapted to geologic fieldwork during EVAs

Hurtado, J. M., Jr.↗
NASA NTRS2011

Desert Rats 2010 Operations Tests: Insights from the Geology Crew Members

Desert Research and Technology Studies (Desert RATS) is a multi-year series of tests of NASA hardware and operations deployed in the high desert of Arizona. Conducted annually since 1997, these activities exercise planetary surface hardware and operations in relatively harsh conditions where long-distance, multi-day roving is achievable. Such activities not only test vehicle subsystems, they also stress communications and operations systems and enable testing of science operations approaches that advance human and robotic surface exploration capabilities. Desert RATS 2010 tested two crewed rovers designed as first-generation prototypes of small pressurized vehicles, consistent with exploration architecture designs. Each rover provided the internal volume necessary for crewmembers to live and work for periods up to 14 days, as well as allowing for extravehicular activities (EVAs) through the use of rear-mounted suit ports. The 2010 test was designed to simulate geologic science traverses over a 14-day period through a volcanic field that is analogous to volcanic terrains observed throughout the Solar System. The test was conducted between 31 August and 13 September 2010. Two crewmembers lived in and operated each rover for a week with a "shift change" on day 7, resulting in a total of eight test subjects for the two-week period. Each crew consisted of an engineer/commander and an experienced field geologist. Three of the engineer/commanders were experienced astronauts with at least one Space Shuttle flight. The field geologists were drawn from the scientific community, based on funded and published field expertise.

Bleacher, J. E.↗
NASA NTRS1995

A preliminary comparison of two perennially ice-covered lakes in Antarctica: Analogs of past martian lacustrine environments

Perennially ice-covered lakes in the Antarctic have been suggested as analogs to lakes which may have existed on the surface of Mars 3.5 billion years ago. During the 1991-1992 austral summer, a joint Russian/American research effort was directed at studies of ice-covered lakes in the Bunger Hills Oasis, Antarctica (66 deg S, 100 deg E). The primary objective of the expedition was to investigate this ice-free area for features analogous to ancient martian environments that may have been capable of supporting life and to compare the ice-covered lakes of the Bunger Hills with those in the McMurdo Dry Valleys of southern Victoria Land (77 deg S, 166 deg E) as part of the continuing studies of Antarctic-Mars analogs.

Andersen, D. T.↗
NASA NTRS1982

Smoothing splines: Regression, derivatives and deconvolution

The statistical properties of a cubic smoothing spline and its derivative are analyzed. It is shown that unless unnatural boundary conditions hold, the integrated squared bias is dominated by local effects near the boundary. Similar effects are shown to occur in the regularized solution of a translation-kernel intergral equation. These results are derived by developing a Fourier representation for a smoothing spline.

Rice, J.↗
NASA NTRS1979

Navigation and meteorological error equations for some aerodynamic parameters

Mathematical equations for the analysis of the errors that are expected in a set of postflight aerodynamic parameters are presented. The errors are due to inaccuracies in the Shuttle best estimate trajectory and in the meteorological data obtained in support of the flights. The error analysis shows that the parameter vector, Z, and its associated error covariance matrix, C sub Z, is calculated from a given state vector, X, and its associated covariance matrix, C sub X.

Krikorian, M. J.↗