221 research outputs found
Global effects on neoclassical transport in the pedestal with impurities
We present a numerical study of collisional transport in a tokamak pedestal
in the presence of non-trace impurities, using the radially global
neoclassical solver PERFECT [M. Landreman et al. 2014 Plasma Phys. Control.
Fusion 56 045005]. It is known that in a tokamak core with non-trace impurities
present the radial impurity flux opposes the bulk ion flux to provide an
ambipolar particle transport, with the electron transport being negligibly
small. However, in a sharp density pedestal with sub-sonic ion flows the
electron transport can be comparable to the ion and impurity flows.
Furthermore, the neoclassical particle transport is not intrinsically
ambipolar, and the non-ambipolarity of the fluxes extends outside the pedestal
region by the radial coupling of the perturbations. The neoclassical momentum
transport, which is finite in the presence of ion orbit-width scale profile
variations, is significantly enhanced when impurities are present in non-trace
quantities, even if the total parallel mass flow is dominated by the bulk ions
Quasi-phasematching of harmonic generation via multimode beating in waveguides
A new scheme for quasi-phasematching high harmonic generation (HHG) in gases
is proposed. In this, the rapid variation of the axial intensity resulting from
excitation of more than one mode of a waveguide is used to achieve quasi
phasematching. Numerical modeling demonstrates enhancement of the harmonic
signal over that achieved for a single coherence length by factors >10^4.Comment: 6 pages including 3 figure
Impurity flows and plateau-regime poloidal density variation in a tokamak pedestal
In the pedestal of a tokamak, the sharp radial gradients of density and
temperature can give rise to poloidal variation in the density of impurities.
At the same time, the flow of the impurity species is modified relative to the
conventional neoclassical result. In this paper, these changes to the density
and flow of a collisional impurity species are calculated for the case when the
main ions are in the plateau regime. In this regime it is found that the
impurity density can be higher at either the inboard or outboard side. This
finding differs from earlier results for banana- or Pfirsch-Schl\"uter-regime
main ions, in which case the impurity density is always higher at the inboard
side in the absence of rotation. Finally, the modifications to the impurity
flow are also given for the other regimes of main-ion collisionality.Comment: 15 pages, 5 figures, submitted to Physics of Plasma
Impurities in a non-axisymmetric plasma: transport and effect on bootstrap current
Impurities cause radiation losses and plasma dilution, and in stellarator
plasmas the neoclassical ambipolar radial electric field is often unfavorable
for avoiding strong impurity peaking. In this work we use a new continuum
drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative
Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014)
042503] which employs the full linearized Fokker-Planck-Landau operator, to
calculate neoclassical impurity transport coefficients for a Wendelstein 7-X
(W7-X) magnetic configuration. We compare SFINCS calculations with theoretical
asymptotes in the high collisionality limit. We observe and explain a
1/nu-scaling of the inter-species radial transport coefficient at low
collisionality, arising due to the field term in the inter-species collision
operator, and which is not found with simplified collision models even when
momentum correction is applied. However, this type of scaling disappears if a
radial electric field is present. We also use SFINCS to analyze how the
impurity content affects the neoclassical impurity dynamics and the bootstrap
current. We show that a change in plasma effective charge Zeff of order unity
can affect the bootstrap current enough to cause a deviation in the divertor
strike point locations.Comment: 36 pages, 13 figure
Addressing Sexual Violence as Student Affairs Work
In this chapter, we outline the challenges campuses face in addressing sexual violence and Title IX compliance. We argue that there are critical roles for student affairs professionals in Title IX work in developing effective campus sexual violence prevention and response strategies.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142989/1/ss20251.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142989/2/ss20251_am.pd
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