5,795 research outputs found
Interpretation of the I-Regime and transport associated with relevant heavy particle modes
The excitation of a novel kind of heavy particle [1, 2] mode at the edge of the plasma column is
considered as the signature of the I-con nement Regime [3{7]. The outward transport of impurities
produced by this mode is in fact consistent with the observed expulsion of them from the main
body of the plasma column (a high degree of plasma purity is a necessary feature for fusion burning
plasmas capable of approaching ignition). Moreover, the theoretically predicted mode phase velocity,
in the direction of the electron diamagnetic velocity, has been con rmed by relevant experimental
analyses [8] of the excited
uctuations (around 200 kHz). The plasma \spontaneous rotation" in the
direction of the ion diamagnetic velocity is also consistent, according to the Accretion Theory [9] of
this phenomenon, with the direction of the mode phase velocity. Another feature of the mode that
predicted by the theory is that the I-Regime exhibits a knee of the ion temperature at the edge of
the plasma column but not one of the particle density as the mode excitation factor is the relative
main ion temperature gradient exceeding the local relative density gradient. The net plasma current
density appearing in the saturation stage of the relevant instability, where the induced particle and
energy
uxes are drastically reduced, is associated with the signi cant amplitudes of the poloidal
magnetic eld
uctuations [6, 7] observed to accompany the density
uctuations. The theoretical
implications of the signi cant electron temperature
uctuations [10] observed are discussed.United States. Dept. of Energ
Learning physics in context: a study of student learning about electricity and magnetism
This paper re-centres the discussion of student learning in physics to focus
on context. In order to do so, a theoretically-motivated understanding of
context is developed. Given a well-defined notion of context, data from a novel
university class in electricity and magnetism are analyzed to demonstrate the
central and inextricable role of context in student learning. This work sits
within a broader effort to create and analyze environments which support
student learning in the sciencesComment: 36 pages, 4 Figure
Microwave response of vortices in superconducting thin films of Re and Al
Vortices in superconductors driven at microwave frequencies exhibit a
response related to the interplay between the vortex viscosity, pinning
strength, and flux creep effects. At the same time, the trapping of vortices in
superconducting microwave resonant circuits contributes excess loss and can
result in substantial reductions in the quality factor. Thus, understanding the
microwave vortex response in superconducting thin films is important for the
design of such circuits, including superconducting qubits and photon detectors,
which are typically operated in small, but non-zero, magnetic fields. By
cooling in fields of the order of 100 T and below, we have characterized
the magnetic field and frequency dependence of the microwave response of a
small density of vortices in resonators fabricated from thin films of Re and
Al, which are common materials used in superconducting microwave circuits.
Above a certain threshold cooling field, which is different for the Re and Al
films, vortices become trapped in the resonators. Vortices in the Al resonators
contribute greater loss and are influenced more strongly by flux creep effects
than in the Re resonators. This different behavior can be described in the
framework of a general vortex dynamics model.Comment: Published in Physical Review B 79,174512(2009); preprint version with
higher resolution figures available at
http://physics.syr.edu/~bplourde/bltp-publications.ht
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