Speaker
Dmitry L. Rudakov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1032.pdf
45 EPS Conference on Plasma Physics 13103
High bandwidth electron temperature measurements in DIII-D divertor*
D.L. Rudakov1, J.A. Boedo1, A.G. McLean2, J.G. Watkins3
1
University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0417, USA
2
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
3
Sandia National Laboratory, 7011 East Avenue, Livermore, CA 94550, USA
For the first time electron temperature (Te) fluctuations have been measured in different
regions of a tokamak divertor using a fast (100 kHz bandwidth) Langmuir probe based
diagnostic. The diagnostic, recently installed on the fast reciprocating probe in the lower
divertor [1], is based on the digital detection of harmonics in a single probe current spectrum,
and is similar to that used on the mid-plane reciprocating probe in DIII-D [2]. Here we report
the initial measurements of Te fluctuations in the divertor and compare their properties to
those measured in the outboard SOL by the pre-existing diagnostic.
Measurements were performed at the outboard divertor scrape-off layer (SOL) radially
outside of the Outer Strike Point (OSP), private flux region, and inboard divertor SOL
(inboard of the inner divertor leg) of Lower Single Null discharges. For this initial work,
results concentrate on low-density low-confinement (L-mode) discharges with attached OSP,
where the Te data from the new harmonic diagnostic are in reasonable agreement with the
Divertor Thomson Scattering measurements.
In all cases the relative (root-mean-square to mean) Te fluctuation levels in the divertor were
between 0.3 – 1.0, which is higher than 0.2 – 0.5 measured in the same discharges in the
outboard SOL by the mid-plane probe. Spectral characteristics of Te fluctuations vary with
position in the SOL; comparisons between the divertor and outboard SOL are presented and
discussed. The fluctuation spectra have measurable energy up to the bandwidth of the
diagnostics (100 kHz) in both regions, while the frequency roll-off tends to be slower in the
divertor compared to the outboard SOL.
[1] J.G. Watkins, et al., Rev. Sci. Instrum. 68, 373 (1997)
[2] D.L. Rudakov, et al., Rev. Sci. Instrum. 72, 453 (2001)
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*This material is based upon work supported by the U.S. Department of Energy under Award Number(s) DE-
FG02-07ER54917, DE-FC02-04ER54698 DE-AC52-07N27344, and DE-NA0003525.
