Contributors: Vail, P. J., Boyer, M. D., Welander, A. S., Kolemen, E., U.S. Department of Energy contract number DE-AC02-09CH11466, U. S. Department of Energy
... This paper presents the development of a physics-based multiple-input-multiple-output algorithm for real-time feedback control of snowflake divertor (SFD) configurations on the National Spherical Torus eXperiment Upgrade (NSTX-U). A model of the SFD configuration response to applied voltages on the divertor control coils is first derived and then used, in conjunction with multivariable control synthesis techniques, to design an optimal state feedback controller for the configuration. To demonstrate the capabilities of the controller, a nonlinear simulator for axisymmetric shape control was developed for NSTX-U which simultaneously evolves the currents in poloidal field coils based upon a set of feedback-computed voltage commands, calculates the induced currents in passive conducting structures, and updates the plasma equilibrium by solving the free-boundary Grad-Shafranov problem. Closed-loop simulations demonstrate that the algorithm enables controlled operations in a variety of SFD configurations and provides capabilities for accurate tracking of time-dependent target trajectories for the divertor geometry. In particular, simulation results suggest that a time-varying controller which can properly account for the evolving SFD dynamical response is not only desirable but necessary for achieving acceptable control performance. The algorithm presented in this paper has been implemented in the NSTX-U Plasma Control System in preparation for future control and divertor physics experiments.
Contributors: Brown, Jessica
... I estimate the impact of public pre-kindergarten for 4-year-olds on the provision of private child care for younger children by considering New York City's 2014 Universal Pre-K expansion. Private child care facilities often care for children from infancy or toddlerhood through pre-K. A public option for older children could therefore affect availability, prices, or quality of care for younger children. This effect could be positive or negative depending on the structure of the child care market, the design of the public pre-K program, and parent preferences. I use a panel dataset covering all licensed child care facilities in New York City and a difference-in-differences strategy that compares changes over time for neighborhoods with more versus fewer new public pre-K sites. I estimate that the public pre-K program reduced the capacity for children younger than 2 years old at private child care centers by 2,700 seats. The entire decrease in capacity occurs in areas with high poverty, and this decline was not o set by an increase in provision in the home day care market. In complementary analysis, I find a within- center increase in public complaints and inspection violations for day care centers that are closer to new public pre-K sites, suggesting a decrease in quality due to the increased competition from public pre-K. A back-of-the-envelope calculation indicates that for every seven 4-year-olds who shifted from day care centers to public pre-K, there was a reduction of one day care center seat for children under the age of 2.
Contributors: Ludlow, Peter
Contributors: New Jersey Institute for Social Justice
... This report reviews the history of juvenile justice in New Jersey, and details racial disparities in police contact and sentencing. It includes six policy proposals to "fundamentally transform" the juvenile justice system in New Jersey.
Initial transport and turbulence analysis and gyrokinetic simulation validation in NSTX-U L-mode plasmas
Contributors: Guttenfelder, W., Kaye, S.M., Kreite, D.M., Bell, R.E., Diallo, A., LeBlanc, B.P., McKee, G.R., Podesta, M., Sabbagh, S.A., Smith, D.R.
... Transport analysis, ion-scale turbulence measurements, and initial linear and nonlinear gyrokinetic simulations are reported for a transport validation study based on low aspect ratio NSTX-U L-mode discharges. The relatively long, stationary L-modes enabled by the upgraded centerstack provide a more ideal target for transport validation studies that were not available during NSTX operation. Transport analysis shows that anomalous electron transport dominates energy loss while ion thermal transport is well described by neoclassical theory. Linear gyrokinetic GYRO analysis predicts that ion temperature gradient (ITG) modes are unstable around normalized radii $\rho$=0.6-0.8, although $E\timesB$ shearing rates are larger than the linear growth rates over much of that region. Deeper in the core ($\rho$=0.4-0.6), electromagnetic microtearing modes (MTM) are unstable as a consequence of the relatively high beta and collisionality in these particular discharges. Consistent with the linear analysis, local, nonlinear ion-scale GYRO simulations predict strong ITG transport at $\rho$=0.76, whereas electromagnetic MTM transport is important at $\rho$=0.47. The prediction of ion-scale turbulence is consistent with 2D beam emission spectroscopy (BES) that measures the presence of broadband ion-scale fluctuations. Interestingly, the BES measurements also indicate the presence of bi-modal poloidal phase velocity propagation that could be indicative of two different turbulence types. However, in the region between ($\rho$=0.56, 0.66), ion-scale simulations are strongly suppressed by the locally large $E\timesB$ shear. Instead, electron temperature gradient (ETG) turbulence simulations predict substantial transport, illustrating electron-scale contributions can be important in low aspect ratio L-modes, similar to recent analysis at conventional aspect ratio. However, agreement within experimental uncertainties has not been demonstrated, which requires additional simulations to test parametric sensitivities. The potential need to include profile-variation effects (due to the relatively large value of $\rho_*$=$\rho_i$/a at low aspect ratio), including electromagnetic and possibly multi-scale effects, is also discussed.