708 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
Recommended from our members
Radial mode structure of curvature-driven instabilities in EBT
Viewgraphs describe the theoretical treatment of the radial mode structure of plasma instabilities in the Elmo Bumpy Torus. The calculation retains nonlocal structure of the modes, connects inner and outer ring regions together, uses a self-consistent finite ..beta.., includes the relativistic effects for the hot electron ring, and examines a wide range of parameters. (WRF
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
Electron cyclotron heating can drastically alter reversed shear Alfven eigenmode activity in DIII-D through finite pressure effects
A recent DIII-D experiment investigating the impact of electron cyclotron heating (ECH)
on neutral beam driven reversed shear Alfvén eigenmode (RSAE) activity is presented. The
experiment includes variations of ECH injection location and timing, current ramp rate, beam
injection geometry (on/off-axis), and neutral beam power. Essentially all variations carried out
in this experiment were observed to change the impact of ECH on AE activity significantly.
In some cases, RSAEs were observed to be enhanced with ECH near the off-axis minimum
in magnetic safety factor (qmin), in contrast to the original DIII-D experiments where the
modes were absent when ECH was deposited near qmin. It is found that during intervals
when the geodesic acoustic mode (GAM) frequency at qmin is elevated and the calculated
RSAE minimum frequency, including contributions from thermal plasma gradients, is very
near or above the nominal TAE frequency (fTAE), RSAE activity is not observed or RSAEs
with a much reduced frequency sweep range are found. This condition is primarily brought
about by ECH modification of the local electron temperature (Te) which can raise both the
local Te at qmin as well as its gradient. A q-evolution model that incorporates this reduction
in RSAE frequency sweep range is in agreement with the observed spectra and appears to
capture the relative balance of TAE or RSAE-like modes throughout the current ramp phase
of over 38 DIII-D discharges. Detailed ideal MHD calculations using the NOVA code show
both modification of plasma pressure and pressure gradient at qmin play an important role
in modifying the RSAE activity. Analysis of the ECH injection near the qmin case where no
frequency sweeping RSAEs are observed shows the typical RSAE is no longer an eigenmode
of the system. What remains is an eigenmode with poloidal harmonic content reminiscent of
the standard RSAE, but absent of the typical frequency sweeping behavior. The remaining
eigenmode is also often strongly coupled to gap TAEs. Analysis with the non-perturbative
gyro fluid code TAEFL confirms this change in RSAE activity and also shows a large drop in
the resultant mode growth rates.RCUK Energy Programme EP/I50104
- …