325 research outputs found
Comparison of particle trajectories and collision operators for collisional transport in nonaxisymmetric plasmas
In this work, we examine the validity of several common simplifying
assumptions used in numerical neoclassical calculations for nonaxisymmetric
plasmas, both by using a new continuum drift-kinetic code and by considering
analytic properties of the kinetic equation. First, neoclassical phenomena are
computed for the LHD and W7-X stellarators using several versions of the
drift-kinetic equation, including the commonly used incompressible-ExB-drift
approximation and two other variants, corresponding to different effective
particle trajectories. It is found that for electric fields below roughly one
third of the resonant value, the different formulations give nearly identical
results, demonstrating the incompressible ExB-drift approximation is quite
accurate in this regime. However, near the electric field resonance, the models
yield substantially different results. We also compare results for various
collision operators, including the full linearized Fokker-Planck operator. At
low collisionality, the radial transport driven by radial gradients is nearly
identical for the different operators, while in other cases it is found to be
important that collisions conserve momentum
Anderson localization of ballooning modes, quantum chaos and the stability of compact quasiaxially symmetric stellarators
The radially local magnetohydrodynamic(MHD) ballooning stability of a compact, quasiaxially symmetric stellarator (QAS), is examined just above the ballooning beta limit with a method that can lead to estimates of global stability. Here MHDstability is analyzed through the calculation and examination of the ballooning modeeigenvalue isosurfaces in the 3-space (s,α,θk); s is the edge normalized toroidal flux, α is the field linevariable, and θk is the perpendicular wave vector or ballooning parameter. Broken symmetry, i.e., deviations from axisymmetry, in the stellarator magnetic field geometry causes localization of the ballooning mode eigenfunction, and gives rise to new types of nonsymmetric eigenvalue isosurfaces in both the stable and unstable spectrum. For eigenvalues far above the marginal point, isosurfaces are topologically spherical, indicative of strong “quantum chaos.” The complexity of QAS marginal isosurfaces suggests that finite Larmor radius stabilization estimates will be difficult and that fully three-dimensional, high-nMHD computations are required to predict the beta limit.Research supported by U.S. DOE Contract No. DEAC02-76CH0373.
John Canik held a U.S. DOE National
Undergraduate Fellowship at Princeton Plasma Physics
Laboratory, during the summer of 2000
Fast Magnetic Reconnection Due To Anisotropic Electron Pressure
A new regime of fast magnetic reconnection with an out-of-plane (guide)
magnetic field is reported in which the key role is played by an electron
pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations
of state in the generalized Ohm's law, which even dominates the Hall term. A
description of the physical cause of this behavior is provided and
two-dimensional fluid simulations are used to confirm the results. The electron
pressure anisotropy causes the out-of-plane magnetic field to develop a
quadrupole structure of opposite polarity to the Hall magnetic field and gives
rise to dispersive waves. In addition to being important for understanding what
causes reconnection to be fast, this mechanism should dominate in plasmas with
low plasma beta and a high in-plane plasma beta with electron temperature
comparable to or larger than ion temperature, so it could be relevant in the
solar wind and some tokamaks.Comment: 5 pages, 2 figures, accepted for publication as a letter in Physics
of Plasma
Translating evidence into practice : ACOs’ use of care plans for patients with complex health needs
Background
Care plans are an evidence-based strategy, encouraged by the Centers for Medicare and Medicaid Services, and are used to manage the care of patients with complex health needs that have been shown to lead to lower hospital costs and improved patient outcomes. Providers participating in payment reform, such as accountable care organizations, may be more likely to adopt care plans to manage complex patients.
Objective
To understand how Medicare accountable care organizations (ACOs) use care plans to manage patients with complex clinical needs.
Design
A qualitative study using semi-structured interviews with Medicare ACOs.
Participants
Thirty-nine interviews were conducted across 18 Medicare ACOs with executive-level leaders and associated clinical and managerial staff.
Approach
Development, structure, use, and management of care plans for complex patients at Medicare ACOs.
Key Results
Most (11) of the interviewed ACOs reported using care plans to manage care of complex patients. All care plans include information about patient history, current medical needs, and future care plans. Beyond the core elements, care plans included elements based on the ACO’s planned use and level of staff and patient engagement with care planning. Most care plans were developed and maintained by care management (not clinical) staff.
Conclusions
ACOs are using care plans for patients with complex needs, but their use of care plans does not always meet the best practices. In many cases, ACO usage of care plans does not align with prescribed best practices: ACOs are adapting use of care plans to better fit the needs of patients and providers
Study of the neoclassical radial electric field of the TJ-II flexible heliac
Calculations of the monoenergetic radial diffusion coefficients are presented
for several configurations of the TJ-II stellarator usually explored in
operation. The neoclassical radial fluxes and the ambipolar electric field for
the standard configuration are then studied for three different collisionality
regimes, obtaining precise results in all cases
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