Post on 28-Aug-2018
transcript
POSTECH Fusion Plasma Research Center
Program
Hyeon K. Park
Physics Department
POSTECH
Pohang, Korea
at
KO-AU Collaboration Workshop
April 27, 2010
NFRI, Daejon, Korea
Introduction
Center for Fusion Plasma Diagnostics and Steady State Operation
Established in June, 2009 with other 4 Institutes
Diagnostic programs
ECEI - MHD physics ( Sawtooth, NTM, ELMs, etc.) and Wave Physics (Alfven waves, ICRF waves, etc.)
MIR - Transport physics (Drift waves, Zonal flow) and Wave Physics (Alfven waves, ICRF waves, etc.)
Spectroscopic area - (BES for transport physics and ITER VUV)
Steady state operation
ECH physics and engineering (ECH launcher w/ PPPL)
LHCD physics and engineering (Antenna design/PPPL,MIT)
Perspective of Future Plasma Diagnostics
Conventional Diagnostics Computer simulation Imaging Diagnostics
Improve predictive capability of MHD physics (Sawtooth, NTM, and RWM)
Analogous to evolution of diagnostic capabilities from Stethoscope to MRI
2D ECE imaging system
ECE measurement is an established tool for electron temperature measurement in high temperature plasmas
Sensitive 1-D array detector, imaging optics, and wide-band mm wave antenna, and IF electronics are required for 2-D imaging system
Te fluctuation measurement Real time fluctuations can be studied up to ~1% level
Fluctuation studies down to 0.1 % level have been performed using long time integration
Conventional 1-D ECE system 2-D ECE imaging system
Sawtooth crash via composite 2-D views Core electron temperature (within
the inversion radius) flattens after crash
Frame 1: Hot spot (m/n=1/1 mode)is in the core before crash
Frame 2: Cold flat area (Island)forms inside the inversion radius as crash starts
Frame 3: Transported heat from the core builds up at the mixing zone (~10 cm layer surrounding the inversion radius)
Accumulated heat in the mixing zone will symmetrically diffuse out in radial direction
Microwave imaging Reflectometry
MIR system is capable of measuring poloidal wavenumbers
simultaneously
Multi-frequency probe beams will measure several radial positions
simultaneously (2-D in poloidal and radial)
2
θ
2
0
k σ1
k 2D
1D fluctuations
2D fluctuations
Verification of theoretical models Remarkable resemblance between 2-D images of the hot spot/Island and
images from the matured stage of the simulation result of the full reconnection model (Sykes et al.)
Quasi-reconnection model (J. Wesson)
H.K. Park et al., PRL 96, 195003 (2006).
H.K. Park et al., PRL 96, 195004 (2006).
Comparative animation
Initial and final stage agreement
with the full reconnection model
is excellent but not in between
Comparison with the ballooning mode model Similarities
Pressure finger in early stage of simulation at low field side (middle figure) is similar to those from 2-D images (“a sharp temperature point”)
Reconnection zone is localized in the toroidal plane (1/3 of the toroidal direction is opened)
Differences
Heat flow is highly collective in experiment and stochastic process of the heat diffusion is clear in simulation.
Differences
Pressure bulge at the high field side is inhibited in simulation
Clear pressure finger at high field side from 2-D images but there should be weak (or no) activity of the ballooning mode at the high field side
Stochastic heat diffusion is clear in simulation but the heat flow is highly collective: stochastic process may not be the dominant mechanism for this case
Low Field Side
High Field Side
Y. Nishimura et. al.
W. Park et. al.
Reconfirm “Crash” on Low and High Field Side
HFS
LFS
t=2.0317525 s
t=2.082992 s t=2.0847422 s
t=2.0332075 s
T. Munsat
Sawtooth in NBI heated TEXTOR plasma
Experimental results for
balanced co- and counter-
neutral beam injection
large amplitude
low frequency
of pre- and postcursor oscillations
1580 1585
time [ms]
1590 1595 1600 1605
prepre post
pre
post
mode characteristics appear to
change rapidly (within <200 s):
kink-like behaviour without indication of reconnexion
tearing-like behaviourwith large saturated island
#66305
H. Soltwisch
New observation in Sawtooth oscillation NBI
Core current density
modification by NBI
Precursor phase
Rotation is CW with
250 microsec. period
No clear reconnection
Before crash time
Postcursor phase
Rotation is CCW with
1 msec. period
Reconnection zone is
reduced and heat leaks
Low field side event
Core current density
modification by NBI
Precursor phase
Similar to LFS
Postcursor phase
Rotation is CCW with
1 msec. period
Reconnection zone is
reduced and heat leaks
through sustained but
Reduced reconnection
zone
High field side event
Reconstruction the post-crash phase
High Field Side
First reconnection is
not complete
First crash is toward
top
Remnants of m=1
mode survives for
~1.5 msec while
reconnection zone
Is reduced.
Low Field Side
First reconnection is
not complete
First crash is away
from this view
Remnants of m=1
mode survives for
~1.5 msec while
reconnection zone
Is reduced.
Imaging and Control of Magnetic Islands
More recently, similar techniques have been used to reconstruct magnetic islands in TEXTOR plasmas.
ECEI enables extraction of island parameters and helps to demonstrate the effects of ECRH on these structures.
I. Classen et al., PRL 98, 035001 (2007)
Observation of ELMS with ECE-Imaging
ASDEX-U, Germany
J. Boom, Oct, 29, 2009
First results !
Imaging of 2D Alfven waves Direct 2D visualization of core MHD perturbation structures
Smaller amplitude perturbations (<10 eV) such Alfven eigenmodes
may be possible to image by integrating the ECEI signal over time.
Tearing mode structure at DIII-DM.A. Van Zeeland et al, Nucl. Fusion
48 (2008) 092002
n=3 Toroidal Alfven
EigenmodeM.A. Van Zeeland et al,
PRL 97, 135001 (2006)
2D structure of RS
Alfven Eigenmode by
ECEI system from DIII-D
KSTAR ECEI View Window (B0=2.0 T)
HFSLow Field Side
High Field Side
LFS
KSTAR ECEI System (2010)
II. Antenna Array
I. Zoom/Focus Optics
+ III. Heterodyne
Electronics
Installation is in progress
Plan for MIR system on KSTAR (2012)
Extensive test of the TEXTOR MIR system at POSTECH
Laboratory test and the Gaussian beam analysis revealed phase-front curvature mismatch existed in the original TEXTOR MIR optics
Optics will be revised to revisit the curvature matching issue
continue Density fluctuation information recovered from the KSTAR MIR together
with the ECEI system will enable visualization of sawtooth crash in unprecedented detail.
Advanced data analysis (cross-coherency, bi-spectral analysis, etc)techniques will provide further diagnostic information such as wave dispersion.
Two frequency system will address “Zonal flow” physics (turbulence motion at two adjacent layers)
Reversal of poloidal rotation by NBI:
Wave-dispersion recovered from MIR
data (TEXTOR). Group velocity Vg
corresponds to the poloidal rotation
velocity.
NBI On
(co-injection)
NBI Off
Beam Emission Spectroscopy (new)
Validation of Nonlinear 3D Simulations
(e.g., GYRO)
Turbulent Particle Flux
nvr
Turbulence Imaging
- Eddy visualization - Velocity field turbulence
Physics Topics
Nonlinear Physics:
- Energy cascade - Growth rate - Reynolds Stress
WHY MEASURE 2D DENSITY FLUCTUATION CHARACTERISTICS?
Imaging diagnostics can provide:
n(r,Z,t), v(r,Z,t)
at high sensitivity in core regions of high performance
discharges
~ ~
R (cm )
Z
(cm )
Zonal Flows:
- Core Zonal Flow Identification - Geodesic Acoustic Mode - Generation & Interaction
Strong Physics Need for Higher Sensitivity 2D Fluctuation
Measurements (k|| << k)
Beam Emission Spectroscopy on KSTAR The LO coupling beamsplitter is re-located within the array box
No wasted power, no LO beam dump
Even and odd channels are separated for more relaxed vertical spacing,
but imaged to the same plane
Summary
POSTECH Fusion Plasma Research Center
Established in June 2010
Objective: Advanced Imaging Diagnostics for MHD and Turbulence
physics
ECEI/MIR/BES
Comprehensive comparison with theoretical models will be used for
validation and verification
MHDs (Sawtooth, NTMs, ELMs)
Turbulence (Drift waves, Zonal flow, streamers, etc.)
Wave study (Alfven waves, ICRF waves, etc.)
Transition physics: L/H at the edge and Transport barrier at the
core
Steady state operation and physics tools (ECH and LHCD)