Visualization Diagnostic (MIR
and ECEI) on KSTAR
N.C. Luhmann, Jr.
Dept. of Applied Science
University of California at Davis
U.S.-Korean Workshop
Opportunities for Expanded Fusion Science and
Technology Collaborations with the KSTAR Project
Three Year Program: $1,501,834
May 19-20, 2004
General Atomics, San Diego, U.S.A.
UC Davis: N.C. Luhmann, Jr. and C.W. Domier
PPPL.: H. Park, E. Mazzucatto, and T. Munsat
UC DAVIS
PLASMA DIAGNOSTICS
GROUP
Outline
 Motivation
 ECE
Imaging (ECEI) and Microwave
Imaging Reflectometry (MIR)
 ECEI
and MIR on TEXTOR
 ECEI
and MIR on KSTAR
Motivation
 Stability
and Confinement Physics of Fusion Plasmas
 Stability
limit can be extended via control of MHD fluctuations
 Radial energy transport physics based on micro-turbulence is an
outstanding problem
 Real time visualization of the physics (MHD and turbulence) in
KSTAR will be invaluable for the physics community and the future of
ITER
 Why
Plasma Visualization?
 Complex
theoretical models are visualized in 3-D (both turbulence
and MHD)
 Experimental visualization of Te of (MHD & turbulence) is now feasible
with recent technology advances
 2-D
Plasma Microwave Imaging Tools
 Electron
Cyclotron Emission Imaging (ECEI)
 Microwave Imaging Reflectometry (MIR)
Outline
 Motivation
 ECE
Imaging (ECEI) and Microwave
Imaging Reflectometry (MIR)
 ECEI
and MIR on TEXTOR
 ECEI
and MIR on KSTAR
2-D ECE Imaging (ECEI)

ECE radiometry is an established tool for Te measurement in hot plasmas.

In conventional radiometry, a single antenna receives all frequencies. In
ECEI, a vertically aligned antenna/mixer array employed as the receiver.

Unique advantages: High spatial and temporal resolution, 2-D correlation.

Real time 2-D imaging utilizing wideband IF electronics and a single
sideband detection method (present 128 channel ECEI system installed on
TEXTOR).
Need for Microwave Imaging Reflectometry
Contour plot of the backward field for fluctuations with an average
value of 1 cm–1 for both poloidal and radial wave numbers, and a
total density fluctuation of 1.0x10–2 (a) and 2x10–2 (b).
2 k0
D
1  σ 2 kθ2
Microwave Imaging Reflectometry (MIR)

Probing beam illuminates
extended region of cutoff layer.

Curvature of the lluminating beam
matched to that of the cutoff
surface (toroidal and poloidal) for
optical robustness and maximized
signal level.

“Virtual cutoff layer” imaged onto
detector array (3 example points
shown). This also eliminates the
phase and amplitude corruption
caused by interference of multiple
reflections.

Detection system shares the same
optical elements.
Outline
 Motivation
 ECE
Imaging (ECEI) and Microwave
Imaging Reflectometry (MIR)
 ECEI
and MIR on TEXTOR
 ECEI
and MIR on KSTAR
TEXTOR Combined ECEI/MIR System

Both ECEI and MIR
share two front-end
optics and window

Mesh beamsplitter
separates the ECEI and
MIR signals

Dual dipole antenna
arrays are used for both
ECEI and MIR

ECEI/MIR optics are
designed to minimize
image spot size

Translatable lens, closest
to array box, allows ECEI
image plane to be moved
radially to match plasma
parameters
TEXTOR port & window
Toroidal and
Poloidal Mirrors
ECEI/MIR System Installed on TEXTOR
MIR RF
Source
ECEI LO
Source
Mirror
ECEI
Array
MIR
Array
Mirror
(Covered)
MIR LO
Source
Focusing
Lens
Observation of Ballooning Modes Before Crash

V(r,t)/<V(r,t)>; < > is
average voltage level

10 identical m=1
oscillations are
averaged

Inversion
radius
(q~1)
bp ~0.4 and S ~5 x
106
• Ip = 400 kA
• BT = 2.3T
• Pnbi = ~3 MW
• Crash time is ~150 msec
• Frame is every ~5 msec
• Total run time is ~1.3 msec
Heat Transfer during Crash Phase of m=1 Mode

Six frames of the crash
process, emphasizing
heat transfer out of the
inversion radius into
mixing zone

Composition of the
three 2-D images (384
pixels) obtained by
varying the toroidal
magnetic fields (2.3T,
2.35T and 2.4T)

Note that the double
white lines are the
estimated inversion
radius.
Magnetic Reconnection and Heat Transfer
Process

Composition of images is
feasible

Local oscillator
variation (desirable)

Magnetic field variation
(2.30T, 2.35T and 2.4T)
was the first choice

No presence of high m
ballooning modes.

Elongation along
poloidal plane ?(W. Park,
et.al., Phys. Fluids B 3, 507 (1991)
Inversion radius
(q~1)
Correlation Observed on MIR Signals Between
Amplitude Modulation and Density Change

Cut-off layer is moving from
the core side to the edge as
density is ramped

Interference pattern
dominated at higher density
and well defined I/Q signal
at a lower density

15/16 channels are
operational
Cross-Coherency Analysis of MIR Signals

Examples of cross-coherency analysis; (a) #10 vs. #9 (~0.66 cm),
(b) #10 vs. #5 (~5.0 cm) and (c) #10 vs. #1 (~9.4 cm)

(d) Average cross-coherency value of frequency bin for #10 wrt the
separation distance of imaging spots for all channels
Poloidal Rotation Measurement via MIR system


(a) Broad frequency spectra and
estimated initial velocity is +21 km/sec
during NBI (co-beam) (4.4 sec)

(b) Narrow frequency spectra after
NBI off. Rotation reverses and settles
at -12 km/sec (4.8 sec)
NBI (CO) is turned off at 4.5 sec
and density change is relatively
small (density evolution and NBI
waveform)
Time history of Poloidal Rotation Induced by NBI

Starts at electron diamagnetic
direction at speed of +21
km/sec

Becomes chaotic during
beam slowing down time
scale

Settles at -12 km/sec during
OH phase.
Outline
 Motivation
 ECE
Imaging (ECEI) and Microwave
Imaging Reflectometry (MIR)
 ECEI
and MIR on TEXTOR
 ECEI
and MIR on KSTAR
KSTAR Characteristic Frequencies
280
2f
240
Frequency (GHz)
200
f
3f
C

C

BT = 3.5 T
 R = 1.8 m
 a = 0.5 m
 ne0 = 1.51020 m–3
ECEI
R
160
f
C
120
MIR

Target ECEI range

155-240 GHz
 -0.5 < r/a < +1.0
80
f
P
40
0
-1
Characteristic frequency
plot for KSTAR plasmas
under typical operating
conditions.

Target MIR range

-0.5
0
Radius r/a
0.5
1
75-155 GHz
 +0.5 < r/a < +1.0
MIR on KSTAR – Conceptual Design
Mirrors

Mirrors
Two large plasma facing stainless steel mirrors are placed within the
vacuum vessel

Poloidally (vertically) curved cylindrical mirror
 Toroidally (horizontally) curved cylindrical mirror

Output signals pass through a relatively small output window
MIR on KSTAR –Side View
MIR plasma coverage: 32 cm (vertical)
ECEI on KSTAR – Conceptual Design
Mirrors
Array
Lenses
Focal plane
Window
ECEI plasma coverage: 50 cm (vertical)

ECEI system to share same plasma facing stainless steel mirrors and
window within the Bay G cassette as the MIR system

Two additional mirrors are placed within the cassette to extend the
plasma coverage

ECEI and MIR focal planes are toroidally separated by ~few cm.
ECEI on KSTAR – Side & Top Views
Side View
Top View
Gaussian beam simulations shown above computed using CODE V
ECEI/MIR Initial System Design

1-D MIR system (16 channels)

Initial system design targeted to 137-140 GHz (r/a ~ 0.75)
 Extendable to 2-D (16x2 to 16x4) with additional millimeter-wave illumination
sources and wideband IF electronics, with no change to MIR optics required

2-D ECEI system (20x12=240 channels)

Initial system design targeted to 163-190 GHz (0.0 < r/a < +0.75), split over
three RF bands
 Extendable to wider instantaneous RF bandwidth with increased IF bandwidth
electronics
 Extendable to higher resolution (32x16 = 512 channels) by decreasing the
inter-element spacing and increasing the number of ECEI electronics modules

Broadband radiation collected by the ECEI/MIR arrays to be
preamplified and sent along low loss microwave cables to IF
electronics boxes, located in close proximity to the arrays

High speed digitizers (16-bit, 1.0 MSample/sec) to be incorporated
into IF electronics boxes, with fiber-optic Gigabit ethernet lines to
route acquired data outside of the KSTAR radiation shield
ECEI Imaging Arrays

The relatively low frequency MIR arrays will
employ the proven dual dipole imaging antennas

Two approaches to realizing the higher
frequency ECEI arrays will be pursued

Fundamental mixers (fIF = fRF – fLO) – proven technology

Subharmonic mixers (fIF = fRF – 2fLO) – utilize lower frequency sources

Extensive simulation and laboratory testing to determine the optimum
choice for KSTAR
Fundamental Mixer
Subharmonic Mixer
160-178 GHz
80-89 GHz
0.5 dBm / channel
0.5 dBm / channel
LO power available
20-30 mW
60-80 mW
Predicted conv. loss
8-14 dB
~10 dB
LO illumination
backside
frontside
LO frequency
Min. LO power required
ECEI Subharmonic Mixer Imaging Array

Employ low cost, solid state LO
sources at half of RF frequency

Ease of combining RF and LO
beams for low loss (front side
illumination more efficient)

Reasonable mixer conversion loss

LO source consists of three Gunn
oscillators and an RF switch
providing LO power at 80 GHz,
84.5 GHz and 89 GHz, respectively

IF frequency range: 3-12 GHz

RF frequency range: 163-190 GHz
Quasi-optical
High Pass Filter
LO
Subharmonic
mixer array
RF
Beam
ECEI Fundamental Mixer Imaging Array

Employ variations of the proven dual dipole antennas

Backside illumination to avoid unnecessary RF losses on input (frontside)

Broadband RF/LO filters to recycle RF and LO power back to the
fundamental mixer for improved conversion loss

LO source consists of one remotely tunable backward wave oscillator
(BWO), with a minimum operating range of 160-178 GHz

IF frequency range: 3-12 GHz (same as for subharmonic mixer)

RF frequency range: 163-190 GHz (same as for subharmonic mixer)

Challenges facing the use of a fundamental mixer imaging array on
KSTAR are:

140-178 GHz BWO (Insight Product Co.) generates only 20-30 mW output power;
insufficient LO power delivered to the mixer diode results in increased conversion
losses (8  14 dB)

Unlike solid state sources, BWOs suffer from lifetime issues limiting long term use
Diagnostic Development Tasks
Tasks
Prototype Development and System
Design
ECEI/MIR Antenna Development
ECEI/MIR Optics Design
Bay G Cassette Design
ECEI Electronics Prototype
Development
MIR Electronics Prototype
Development
Final Instrument Development
Assemble Millimeter-Wave Sources
ECEI/MIR Array Fabrication & Testing
ECEI/MIR Optics Fabrication & Testing
Bay G Cassette Fabrication & Testing
ECEI Electronics Fabrication & Testing
MIR Electronics Fabrication & Testing
Year 1 Year 2 Year 3 Responsibl
1 2 3 4 1 2 3 4 1 2 3 4 e Parties
UCD/PPPL
UCD/PPPL
PPPL
UCD
UCD
UCD
UCD
PPPL
KSTAR
UCD
UCD
KSTAR MICROWAVE DIAGNOSTICS
DESIGN
TOTAL COST* – THREE YEARS: $1,501,834

YEAR ONE:
$508,327

YEAR TWO:
$532,873

YEAR THREE:
$460,634
* Includes $ 300k for PPPL efforts (design, modelling, etc.)
KSTAR Diagnostic Layout
Torus Ion Gauge
RGA
X-ray Crystal Spec.
PN
Basic Diagnostics
Baseline Diagnostics
Mission-oriented
Diagnostics
Magnetic Feedthrough
Inspection Illuminator
Glow Discharge Probe
IR TV
Edge Reflectometer
(CES background)*
B A
P
C
Magnetic Feedthrough
Inspection Illuminator
IR TV
Movable Langmuir Probe
Torus Ion Gauge
RGA
X-ray Crystal Spec.
Soft X-ray Spec.
VUV Survey Spec.
ECH
Magnetic Feedthrough
MSE
CES
BES
*Reciprocating (Movable)
Langmuir Probe
Bolometer Array
X-ray Pinhole Camera
IR TV
Visible/H-alpha TV
X-ray PHA (Kurchatov)
Multichord Vis. Spec.
Soft X-ray Array (KAIST)
Impurity Pellet Injector
ICRH/
FWCD
LHH/
LHCD
Inspection Illuminator
Visible/H-alpha TV
Thomson Optics
(Div. Thomson Optics)*
O
N
NBI (I)
M
D
L
E
K
J
F
I
G H
NBI (II)
MSE(II)
Tan. FIR Int. Laser
mm-Wave Interferometer(SNU) Input (SNU)
Reflectometer (UCD/PPPL)
MIR (UCD/PPPL)
* Dual function system
ECEI
()* not fixed
Thomson Laser Input
Bolometer Array
(CX-NPA)*
ECE Radiometer (KAERI)
ECE Interferometer
ECE GPC
LIF Optics (KAIST/KBSI)
(DNB)*
Visible/H-alpha TV
H-alpha Monitor
Visible Survey Spec.
Visible Brems. Array
Visible Filterscope (KBSI/ORNL)
Magnetic Feedthrough
Inspection Illuminator
Glow Discharge Probe
IR TV
Revised Version: 22 March 2002
Wideband ECEI Mixer Array
Dual
dipole antenna elements

Extremely tight antenna spacing to minimize channel
spacing

Wide tunable RF bandwidth for flexibility

Single lobe antenna patterns to couple well to
Gaussian beams
Detector array
12
10
E-Plane
120GHz
115GHz
110GHz
8
H-Plane
120GHz
115GHz
110GHz
10
8
6
6
4
4
2
2
0
0
-40
-20
0
20
40
-40
-20
Angle
Wide
0
20
Angle
bandwidth baluns (2-10 GHz)

CPS-Microstrip balun uses broadside coupled strip

Measured insertion loss < 2.0 dB from 2-10 GHz
40
2-D ECEI Electronics Overview
 Collect
ECE radiation over
a broad frequency range. LO1
LO4
LO3
LO5
LO6
LO2
LO7
LO8
 Downconvert
with a fixed
frequency local oscillator
(LO) to provide a wide IF
bandwidth input signal.
T1
T2
T3
 Divide
the 3-7 GHz input Microwave
signal into 8 parts, and
Amp
Input
downconvert with a
Signal
distinct LO frequency
for each part: 3.2, 3.8, 4.3,
4.8, 5.3, 5.8, 6.3, 6.8 GHz.
 Mixer
outputs are
bandpass filtered
(5-150 MHz), rectified
and amplified for
acquisition and analysis.
T4
T5
T6
Power
Divider
T7
T8
Mixers
IF Amps
Bandpass
Filters
Detectors
Video
Amps
Local Oscillator & Mixer Modules

A total of 8 local oscillator (LO)
boards are needed to downconvert the 2-D ECEI signals,
with 16 LO outputs at a fixed
frequency.

Each amplified signals from
detection array (16 channels)
are divided into 8 equal parts
(designed on microstrip)
Array Box and Electronics for 128 Channel
ECEI System

Completed ECEI electronics
box, with 16 SMA array inputs
(3-7 GHz) and 128 LEMO
outputs (8 outputs per input)

Completed detection array with
the substrate lens and low-noise
microwave preamplifiers.
Measured ECEI and MIR Focal Plane Patterns
ECEI system antenna response
MIR system antenna response
2-D ECEI Data: Shot #94568

One of the first plasmas to be studied with the 2-D ECEI diagnostic
were neutral beam heated plasmas which exhibited sawteeth
(TEXTOR discharge #94568: BT=2.3 T, Pnbi=3 MW).

Shown below are time histories from two of the 128 ECEI channels.

In the following 2 slides are sample 2-D Te images about the q=1 layer,
generated by averaging 10 identical m=1 oscillations to reduce noise.
Mixer 3
IF Band 8
Mixer 13
IF Band 8