This section describes the settings which control the way that NCLASS is run. NCLASS is a module which allows improved calculation of the plasma resistivity, bootstrap current and radial electric field within the plasma via inclusion of neoclassical effects [1]. NCLASS uses a full multi-species representation of plasma profiles valid for arbitrary geometry and collisionality regimes. It maintains separate velocity profiles for each species and when given a toroidal rotation velocity profile for one species can calculate the rotation profiles for all species as well as the radial electrostatic potential.
NCMODEL: This selects the code to be used, the default is 2, which selects Houlberg's NCLASS Fortran 90 module (2004).
This is the recommended setting.
NLVWNC: Set to TRUE to use NCLASS to analyze the input rotation data and compute the radial electrostatic potential profile.
A full analysis is performed in the range XL1NCVPH < r/a < XL2NCVPH with a simple extrapolation outside this region.
The defaults are XL1NCVPH=0.10 and XL2NCVPH=0.85.
NLTINC: Set this flag to TRUE in order to use the average ion temperature for all species in the NCLASS calcuation. This is the default.
When set to FALSE NCLASS will use the impurity and majority temperatures estimated by the SLVTX routine (See PPPL website).
NLOMGVTR: Set this flag to TRUE in order to specify the that the rotation profile for the NCLASS diagnostic species should be taken
from the rotational data input specified by trigraph OMG or VP2.
NCLASS is sensitive to noise in temperature and pressure gradients. The following options can be used to reduce the impact of this:
NLNCSMOO: Set this to TRUE to activate temperature and density profile smoothing. This recommended.
TAUSMNNC: This sets the smoothing convolution time (tau) for density profiles (time smoothing).
TAUSMTNC: This sets the smoothing convolution time (tau) for temperature profiles (time smoothing).
XSMN_NC: This sets the radial smoothing half width for density profiles (r/a units, spatial smoothing).
XSMT_NC: This sets the radial smoothing half width for temperature profiles (r/a units, spatial smoothing).
NLSAW_NC: Set this to TRUE to reinitialize the time convolutions after each sawtooth event.
Once the smoothing has been performed, the resulting profiles are renormalised to preserve the total particle and energy content of each species.
NLETAW : Set to TRUE to use NCLASS to calculate the plasma resistivity.
XL1NCETA : This specifies a value of r/a below which the neoclassical resistivity transitions smoothly back to the classical limit as r/a->0.
The default value for this is 0.0 but the PPPL website suggests a value of 0.1 may also be appropriate due to physical reasons for doubting the validity of the neoclassical
calculation on axis.
NLBOOT : Set to TRUE to include bootstrap currents in the solution of the poloidal field diffusion equation. By default a neoclassical
model based on an aspect ratio approximation is used.
NLBOOTW : If NLBOOT is set to TRUE this can also be set to TRUE to calculate the neoclassical bootstrap currents
using the NCLASS neoclassical code. This is what is commonly done at JET.
XL1NCJBS : This specifies a value of r/a below which the neoclassical bootstrap current transitions smoothly to 0.0 as r/a->0.
The PPPL website recommends that the default value of 0.1 should be the minimum value of this parameter used.
[1] W.A. Houlberg et al., "Bootstrap Current and Neoclassical Transport in Tokamaks of Arbitrary Collisionality and Aspect Ratio", Phys. Plasmas 4 (9), Sept. 1997, pp 3230-3242.