Measurement and Analysis of Core Turbulence in NSTX

Measurements of core turbulence using a homodyne radial correlation reflectometer (26-40 GHZ) and quadrature reflectometers (30, 42, 49 GHz) have been made in NSTX discharges (Ohmic, NB and RF heated L-modes, and Ohmic H-modes) which have peaked low density profiles for good core access. % Previous measurements in NB-heated L-mode discharges indicated radial correlation lengths ($L_{\mathrm{cr}}$) increasing from $\sim$2 to 10-15 cm over a radius from $\rho$$\sim$0.7 to 0.4. This range of values is typical for most L-mode discharges observed. However for Ohmic H-mode discharges, a sudden decrease in $L_{\mathrm{cr}}$ in the core plasma is seen at the L-H transition. % Changes in fluctuation levels and spectra will also be compared with confinement properties determined via TRANSP. % Analysis of the reflectometer data will be aided by the use of a fast 2-D full-wave code [E.J.\ Valeo, G.J.\ Kramer, R.\ Nazikian, Plasma Phys.Control.\ Fusion 44, L1 (2002)]. % to map the reflectometer response to %turbulence inputs. % The long-term goal is a direct comparison between experimental results and turbulence predictions using the nonlinear gyrokinetic simulation code GYRO.