596 research outputs found
Rotation and Neoclassical Ripple Transport in ITER
Neoclassical transport in the presence of non-axisymmetric magnetic fields
causes a toroidal torque known as neoclassical toroidal viscosity (NTV). The
toroidal symmetry of ITER will be broken by the finite number of toroidal field
coils and by test blanket modules (TBMs). The addition of ferritic inserts
(FIs) will decrease the magnitude of the toroidal field ripple. 3D magnetic
equilibria with toroidal field ripple and ferromagnetic structures are
calculated for an ITER steady-state scenario using the Variational Moments
Equilibrium Code (VMEC). Neoclassical transport quantities in the presence of
these error fields are calculated using the Stellarator Fokker-Planck Iterative
Neoclassical Conservative Solver (SFINCS). These calculations fully account for
, flux surface shaping, multiple species, magnitude of ripple, and
collisionality rather than applying approximate analytic NTV formulae. As NTV
is a complicated nonlinear function of , we study its behavior over a
plausible range of . We estimate the toroidal flow, and hence , using
a semi-analytic turbulent intrinsic rotation model and NUBEAM calculations of
neutral beam torque. The NTV from the ripple dominates
that from lower perturbations of the TBMs. With the inclusion of FIs, the
magnitude of NTV torque is reduced by about 75% near the edge. We present
comparisons of several models of tangential magnetic drifts, finding
appreciable differences only for superbanana-plateau transport at small .
We find the scaling of calculated NTV torque with ripple magnitude to indicate
that ripple-trapping may be a significant mechanism for NTV in ITER. The
computed NTV torque without ferritic components is comparable in magnitude to
the NBI and intrinsic turbulent torques and will likely damp rotation, but the
NTV torque is significantly reduced by the planned ferritic inserts
Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations
Alfven Eigenmodes and magneto-hydrodynamic modes are destabilized in DIII-D
reverse magnetic shear configurations and may limit the performance of the
device. We use the reduced MHD equations in a full 3D system, coupled with
equations of density and parallel velocity moments for the energetic particles
(with gyro-fluid closures) as well as the geodesic acoustic wave dynamics. The
aim of the study consists in finding ways to avoid or minimize MHD and AE
activity for different magnetic field configurations and neutral beam injection
operational regimes. The simulations show at the beginning of the discharge,
before the reverse shear region is formed, a plasma that is AE unstable and
marginally MHD stable. As soon as the reverse shear region appears, ideal MHD
modes are destabilized with a larger growth rate than the AEs. Both MHD modes
and AEs coexist during the discharge, although the MHD modes are more unstable
as the reverse shear region deepens. The simulations indicate the
destabilization of Beta induced AE, Toroidal AE, Elliptical AE and Reverse
Shear AE at different phases of the discharges. A further analysis of the NBI
operational regime indicates that the AE stability can be improved if the NBI
injection is off axis, because on-axis injection leads to AEs with larger
growth rate and frequency. In addition, decreasing the beam energy or
increasing the NBI relative density leads to AEs with larger growth rate and
frequency, so an NBI operation in the weakly resonant regime requires higher
beam energies than in the experiment. The MHD linear stability can be also
improved if the reverse shear region and the q profile near the magnetic axis
are in between the rational surfaces q=2 and q=1, particularly if there is a
region in the core with negative shear, avoiding a flat q profile near the
magnetic axis
Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations
Alfvén Eigenmodes (AE) and magneto-hydrodynamic (MHD) modes are destabilized in DIII-D reverse magnetic shear configurations and may limit the performance of the device. We use the reduced MHD equations in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles (with gyro-fluid closures) as well as the geodesic acoustic wave dynamics, to study the properties of instabilities observed in DIII-D reverse magnetic shear discharges. The aim of the study consists in finding ways to avoid or minimize MHD and AE activity for different magnetic field configurations and neutral beam injection (NBI) operational regimes. The simulations show at the beginning of the discharge, before the reverse shear region is formed, a plasma that is AE unstable and marginally MHD stable. As soon as the reverse shear region appears, ideal MHD modes are destabilized with a larger growth rate than the AEs. Both MHD modes and AEs coexist during the discharge, although the MHD modes are more unstable as the reverse shear region deepens. The simulations indicate the destabilization of Beta induced AE (BAE), Toroidal AE (TAE), elliptical AE (EAE) and reverse shear AE (RSAE) at different phases of the discharges, showing a reasonable agreement between the frequency range of the dominant modes in the simulations and the diagnostic measurements (...)This material based on work is supported both by
the U.S. Department of Energy, Office of Science, under
Contract DE-AC05-00OR22725 with UT-Battelle,
LLC and U.S. Department of Energy, Oce of Science,
Oce of Fusion Energy Sciences, using the DIII-D National
Fusion Facility, a DOE Oce of Science user facility, under Award No. DE-FC02-04ER54698. This research was sponsored in part by the Ministerio of EconomÃa y Competitividad of Spain under project no.ENE2015-68265-P. DIII-D data shown in this paper
can be obtained in digital format by following the links
at https://fusion.gat.com/global/D3D DMP.Publicad
Nonlinear dynamics and transport driven by energetic particle instabilities using a gyro-Landau closure model
Energetic particle (EP) destabilized Alfvén eigenmode (AE) instabilities are simulated for a DIII-D experimental case with a pulsed neutral beam using a gyro-Landau moments model which introduces EP phase-mixing effects through closure relations. This provides a computationally efficient reduced model which is applied here in the nonlinear regime over timescales that would be difficult to address with more complete models. The long timescale nonlinear evolution and related collective transport losses are examined including the effects of zonal flow/current generation, nonlinear energy cascades, and EP profile flattening. The model predicts frequencies and mode structures that are consistent with experimental observations. These calculations address issues that have not been considered in previous modelling: The EP critical gradient profile evolution in the presence of zonal flows/currents, and the dynamical nature of the saturated state. A strong level of intermittency is present in the predicted instability-driven transport; this is connected to the zonal flow growth and decay cycles and nonlinear energy transfers. Simulation of intermittent AE-enhanced EP transport will be an important issue for the protection of plasma facing components in the next generation of fusion devices.This material is based upon work supported by the US Department
of Energy, Office of Science using the DIII-D National
Fusion Facility, a DOE Office of Science user facility, under
Awards DE-AC05-00OR22725, DE-FC02-04ER54698,
and the US DOE SciDAC ISEP Center. Support is also
acknowledged from project 2019-T1/AMB-13648 founded
by the Comunidad de Madrid and Comunidad de Madrid
(Spain)—multiannual agreement with UC3M Excelencia
para el Profesorado Universitario EPUC3M14 Fifth
regional research plan 2016-2020. This research used
resources of the National Energy Research Scientific Computing
Center (NERSC), a US Department of Energy Office
of Science User Facility located at Lawrence Berkeley
National Laboratory, operated under Contract No. DE-AC02-
05CH11231. We would like to thank Matt Beidler of Oak
Ridge National Laboratory for helpful suggestions on this
manuscript
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