STELLOPT Modeling of the 3D Diagnostic Response in ITER Page: 4 of 16
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STELLOPT Modeling of ITER
The heat flux associated with edge localized modes (ELMs) in H-Mode plasmas requires
ITER be able to suppress these phenomena. This must be done to protect the divertor
components and prevent impurity influxes from this region.  The application of
resonant magnetic perturbations (RMPs) through in-vessel coils is one such method
suggested for ITER. This is a likely candidate for ELM control in ITER as various
Tokamaks throughout the world have shown mitigation and suppression of ELMs
through RMP application [2, 3]. However, the extent to which these 3D fields perturb
the plasma boundary has varied between devices. Such variations in boundary shape can
have profound implications on diagnostic interpretation and the ability to reconstruct
plasma equilibria. These variations also limit the minimum plasma-wall gap at which
an experiment may be run. In the MAST device, evidence of up to 5 cm variations
in the plasma boundary toroidally have been documented . In such cases, proper
calculation of plasma stability and transport requires 3D equilibrium reconstruction.
The ability to reconstruct 3D equilibria has been developed for stellarators and
has been extended to Tokamaks with applied 3D fields. The STELLOPT code  has
been designed to fit (in a non-linear, least-squared sense) VMEC three dimensional ideal
MHD equilibria  to various experimental diagnostic measurements around a device (in
both the poloidal and toroidal directions). Originally developed to optimize stellarator
equilibria for desired stability and transport properties, STELLOPT was modified to
match equilibria to diagnostic measurements in the W7-AS device . This work was
later extended to the Large Helical Device , and finally to the DIII-D device . The
effect of discrete toroidal field coils and test blanket modules on the 3D equilibrium of
ITER have been previously evaluated with VMEC [10, 11, 12]. Edge displacements were
found to be less than 0.5 cm suggesting little effect on diagnostic measurements. The
effect of applied RMPs on ITER equilibria have also been examined with other codes
. The results indicate that 'vacuum' RMP calculations, where the vacuum RMP
field is added to an axisymmetric equilibrium model, are incorrect. This motivates an
analysis in which the effect of such 3D fields on diagnostics measurements using a 3D
equilibrium code is performed. In this paper a forward modeling of the 3D diagnostic
responses of ITER is performed using the STELLOPT code. The axisymmetric and
3D equilibrium diagnostics responses of ITER are calculated in axisymmetry and for
an applied RMP field. Here, the in-vessel coil system applies an n = 3 RMP to the
plasma. Comparisons between the axisymmetric and 3D plasma diagnostic response are
presented alongside a sensitivity analysis of the diagnostics measurements to equilibrium
The diagnostic responses of an ITER axisymmetric equilibrium and one in which the in-
vessel coils apply a resonant n = 3 perturbation are examined through forward modeling
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Lazerson, Samuel A. STELLOPT Modeling of the 3D Diagnostic Response in ITER, report, May 7, 2013; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc839563/m1/4/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.