Resolving the Plasma Electron Temperature Pedestal in JET
from Thomson Scattering Core LIDAR Data
D. Stoyanov, M. Beurskens, T. Dreischuh, L. Gurdev, O. Ford, J. Flanagan,
M. Kempenaars, I. Balboa, M.
Walsh and JET EFDA contributors
One of the basic advantages of the JET Core LIDAR Thomson Scattering system is the
measuring of electron temperature
Te and density
ne profiles along the entire line of
sight inside the torus. However, the spatial resolution is of the order of 12-15 cm and thus insufficient for resolving
the narrow pedestal area, typically in the region of a few centimeters. Deconvolution technique
has already been successfully applied to the LIDAR data. In spite of the improved resolution,
the deconvolved Te and
ne profiles remain extended outside the torus wall.
In this work we are performing the next step to estimate the true shape of the
Te pedestal from the Core LIDAR
data as well as its basic parameters such as width, value and position. The method proposed is
based on a preliminary transformation of the LIDAR profiles (step 3cm) to ones sampled with a
new step of 1cm. Then, a convolution procedure with low pass filter characteristics (used in
the deconvolution process) is applied to a specially designed model of the electron
temperature profile with a variable pedestal function. An optimal least square fitting algorithm is applied
to extract the best fit pedestal parameters at a preliminary chosen pedestal shape function.
Results from the processing of a set of Core LIDAR data from different JET pulses for plasmas of
high and low triangularity will be presented. The comparison with the High Resolution
Thomson Scattering (HRTS) displays a good coincidence of the
mean Te pedestal estimates within
H-mode with best fits of HRTS pedestals. At this stage the method is effective for a set of
3-4 successive laser pulses (time resolution 0.75-1s). Possible upgrades of the LIDAR system
with modern detectors and acquisition providing better signal-to-noise ratio, better spatial
resolution and a higher sampling rate, and the improved method performance in this case will be discussed.
Preprint of Paper to be submitted for publication in Proceedings of the
37th EPS Conference on Plasma Physics, Dublin, Ireland.
(21st June 2010 - 25th June 2010)