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)