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Feasibility of Correlation ECE Diagnostic at C-Mod
hne i
ne (0)
Te (0)
Ti (0)
Table 1. Experimental parameters for the typical L-mode Alcator C-Mod plasmas
heated with 1-2 MW of ICRH that are considered in this feasibility study.
5.4 T
0.6-1.2 MA
1-2 MW
0.7 − 1.0 ×1020 m−3
1.0 − 1.5 ×1020 m−3
3.0 − 3.2 keV
1.6 − 3.0 keV
from TRANSP from long steady periods of the discharge are time-averaged in order to
estimate uncertainties in calculated heat fluxes. These uncertainties in the TRANSP
outputs are due to variations in the experimental profiles in time, and provide a
reasonable estimate of the experimental uncertainties in the reported heat flux. For
the plasmas here, we find uncertainties for TRANSP ion and electron heat fluxes in the
range 10 − 15%. Other methods of estimated the uncertainties in TRANSP outputs
have been discussed elsewhere [40].
4. Results from Local GYRO Simulations
In order to determine whether or not a CECE diagnostic is feasible, the nonlinear
GYRO simulations are used to obtain predicted ranges for three turbulence parameters:
fluctuation level, T̃e /Te , peak poloidal wavenumber, kθ ρs , and the radial correlation
length, Lr . More than thirty GYRO simulations were used in this study, including
local and global simulations. Local simulation results are used with synthetic diagnostic
models in order to generate quantitive predictions for the required CECE spot-size and
the effect of an off mid-plane view. One local simulation is discussed here in detail.
Global simulations are discussed later in Section 6.
The local simulation of interest was prepared using data from C-Mod discharge
1100308003 (BT = 5.46 T, Ip = 0.8 MA) at t = 1.0 sec during the current flattop. This
is a typical sawtoothing L-mode plasma (q0 = 1, q95 = 4.5) with PRF = 1.2 MW of
Ion Cyclotron Resonance Heating. The central density is ne (0) = 1.4 × 1020 m−3 , line
averaged density hne i = 0.95×1020 m−3 . The central electron temperature is Te (0) = 3.1
keV. Input parameters for this particular local L-mode simulation are listed in Table 2.
In the local GYRO simulation, the Miller equilibrium model is used [41] and E × B
shear is included using the Waltz-Miller formula. The simulations are electrostatic, but
GYRO can include electromagnetic effects.
Gyrokinetic ions and drift-kinetic electrons
are used, with realistic mass ratio ( mi /me = 60). No dynamic impurity ions are
included in this particular simulation, and quasineutrality forces ion and electron density