ECE Imaging on
The DIII-D ECEI system
is a dual-array configuration ECE Imaging on DIII-D ECE Imaging on DIII-D providing ECE Imaging on DIII-Dimages of the electron
temperature at two distinct plasma locations. The images may be independently
configured to capture adjacent regions or opposing sides of the magnetic axis.
Additionally, the vertical and radial coverage of each image may be varied over
a broad range.
The dual-array ECEI installation on DIII-D
 is the 3rd generation imaging system of its kind. It improves on the 1st
and 2nd generation TEXTOR designs.
Some of its improved capabilities include:
Above: Laboratory setup of the DIII-D ECEI optics and detector arrays.
Above: ECEI system installed at the 270 degree midplane
port on DIII-D.
Frequency band detectable by ECEI on DIII-D (yellow). For this particular discharge,
the low-field array covers the region indicated by the overlaid lower green
band, and the high-field array covers the region of the upper green band. The
2nd harmonic ECE is plotted in blue and the right-handed X-mode
cutoff is the dark green curve.
Poloidal cross-section of DIII-D demonstrating the
variation in ECEI coverage with vertical zoom and variable LO frequency.
Above: Mini-lens detector
array. 24 vertical channels are accommodated in the same toroidal
plane by using a beam splitter to apportion signal to adjacent channels. Propagation directions of the LO and
ECE signals are indicated.
Above: Schematic of mini-lens detector
Perhaps the most impressive aspect of the dual-array
ECEI system on DIII-D is the exciting data it has been collecting. Of the many
experiments in which it has been employed, some of the highlights are described
instability in tokamak plasmas is observed to cause a
rearrangement of the internal current profile as well as redistribution of
particles and temperature. The MHD mode, ultimately leading to the crash, is a
relatively large magnetic perturbation, characterized by toroidal/poloidal mode numbers n/m=1/1 and typically low frequency (≤10kHz).
Nailing down a solid physics understanding of the crash event (which takes
place on the order of 10s-100s of microseconds) has eluded physicists for
decades since the instability’s discovery in the 1970s. Now, with imaging
diagnostics, such as ECEI, we are able to capture the collapse of the electron
temperature at the sawtooth crash with unsurpassed
clarity. 2-dimensional data such as this provides an unambiguous measurement to
which simulation models can compare.
Above: Select ECEI frames taken during the last precursor oscillation
leading up to the sawtooth crash. The dashed white
line in the first frame is the inversion radius.
Unlike the sawtooth
instability, Alfvén eigenmodes
(AEs) are low-amplitude and typically characterized by medium to high toroidal mode number (n) and medium to high frequency. In
many cases, multiple-n modes are simultaneously and/or sequentially
destabilized in the plasma. The diagnosis of AEs in tokamaks
is particularly important to the study of energetic ions. Sizable losses of
energetic ions by AEs associated with mode-particle resonances have been
well-documented on many tokamaks. An understanding of
the stability limits and mode structure of AEs has become a high-priority
research task in the fusion community. Imaging diagnostics, such as ECEI,
provide a critical tool to the identification of such modes.
Above: (a) the symmetric reverse-shear AE (RSAE) structure
predicted by ideal MHD is shown. TAEFL demonstrates that fast-ion
contributions may alter the eigenmode structure,
inducing symmetry breaking as shown in (b). Experimental measurement by ECEI,
(c), confirms these predictions providing an opportunity for model validation
 Tobias B.J., et al,
of electron cyclotron emission imaging instrument on the DIII-D tokamak and first data”
Rev. Sci. Instrum. 81, 10D928 (2010).
B.J., et al, “Fast Ion Induced
Shearing of 2D Alfvén Eigenmodes
Measured by Electron Cyclotron Emission Imaging” Phys. Rev. Lett. 106, 075003 (2011).
UC Davis has fabricated and
installed multichannel ECE Imaging systems on a number of fusion plasma tokamaks across the world. Follow the links below for a
description of the systems involved
ECE Imaging on the EAST
tokamak in China
ECE Imaging on the
KSTAR tokamak in Korea
Imaging on the TEXTOR tokamak in Germany
ECE Imaging on the
TEXT-U tokamak in the U.S.A. (Reference Only)
Comments to: Calvin Domier