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Visualization Technique for MHD and Visualization Technique for MHD and Transport Physics in tokamaks

Hyeon K. Park Physics Department at POSTECH Pohang, Korea at Toki Conference December 08-11, 2009 Collaborators

• G. Yun, W. Lee, M.J. Choi, N.C. Luhmann, Jr.,

C.W. Domier, A.J.H. Donné, I. Classen, T. Munsat C.W. Domier, A.J.H. Donné, I. Classen, T. Munsat

Introduction Introduction

Study of “Sawtooth Oscillation”

Visualization of T and n fluctuations in high temperature Visualization of Te and ne fluctuations in high temperature plasmas (“ultimate diagnostic system”,1998 APS) Principle of ECE imaging system Review of the “Sawtooth oscillation”

Advances of Visualization Tools and New Findings

Improved ECEI system and its application

• Intermittent reconnection process of sawtooth crash
• Other MHDs (m=2 mode, ELMS)
• Objectives in DIII-D, ASDEX-U and KSTAR

Progress of MIR system for density turbulence based transport physics p y

Evolution of Plasma Diagnostics Evolution of Plasma Diagnostics

Conventional Diagnostics Computer simulation Imaging Diagnostics Improve predictive capability of MHD physics (Sawtooth NTM and RWM) Improve predictive capability of MHD physics (Sawtooth, NTM, and RWM) Analogous to evolution of diagnostic capabilities from Stethoscope to MRI

2D ECE imaging system g g y

ECE measurement is an established tool for electron temperature Conventional 1-D ECE system 2-D 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 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 Fluctuation studies down to 0.1 % level have been performed using long time integration

Sawtooth crash via composite 2-D views p

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) Frame 2: Cold flat area (Island) forms inside the inversion radius as crash starts Frame 3: Transported heat from 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

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.) Comparative animation Quasi-reconnection model Initial agreement with the full reconnection model is excellent

Comparison with the ballooning mode model

L Fi ld Sid 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”)

Low Field Side

( a sharp temperature point ) Reconnection zone is localized in the toroidal plane (1/3

• f the toroidal direction is opened)

Differences

Heat flow is highly collective in experiment and stochastic process of the heat diffusion is clear in simulation.

Diff High Field Side Differences

Pressure bulge at the high field side is inhibited in simulation Clear pressure finger at high field side from 2-D images p g g g 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

Mini Mini-

• Lens based Array Detectors

Lens based Array Detectors

ECE signal

• The LO coupling beamsplitter is re

The LO coupling beamsplitter is re-

• located

located within the array box within the array box

• No wasted power, no LO beam dump

No wasted power, no LO beam dump

Filtered ECE Dichroic Plate (High Pass Filter) Beamsplitter

• Even and odd channels are separated for

Even and odd channels are separated for more relaxed vertical spacing, but imaged to more relaxed vertical spacing, but imaged to the same plane the same plane

Local Beamsplitter IF frequency Mini-lens Array,

Odd Channel Even Channel

Oscillator IF frequency y, Even Channels

Beamsplitter Channel Mini-Lens Array Mini-Lens Array

Mini-lens Array, Odd Channels

Signal LO g

Improved Video Electronics Improved Video Electronics

Highly linear video response to Highly linear video response to temperature fluctuations up to temperature fluctuations up to 50% 50%

1.5 2 2.5

50% 50% Video BW variable from 12.5 to Video BW variable from 12.5 to 400 kHz and compatible with 400 kHz and compatible with

0.5 1 Volts

±2.5 V digital acquisition 2.5 V digital acquisition Proprietary designs developed Proprietary designs developed and tested at UC Davis and tested at UC Davis

• 1.5
• 1
• 0.5

Measured Response Linear Fit

and tested at UC Davis and tested at UC Davis

• 1
• 0.5

0.5 1

• 2

Δ Power / Power

Reconfirm “Crash” on Low and High Field Side Reconfirm “Crash” on Low and High Field Side g

HFS

t=2.0317525 s t=2.0332075 s

LFS

t=2.082992 s t=2.0847422 s t 2.082992 s t 2.0847422 s

Intermittent Reconnection Process Intermittent Reconnection Process

Intermittent Reconnection Process Intermittent Reconnection Process

High Field Side First reconnection is Low Field Side First reconnection is not complete First crash is toward top not complete First crash is away from this view top Remnants of m=1 mode survives for from this view Remnants of m=1 mode survives for For ~1.5 msec For ~1.5 msec

Re-reconnection process p

Imaging and Control of Magnetic Islands Imaging and Control of Magnetic Islands g g g g g g

More recently, similar techniques have been used to reconstruct magnetic More recently, similar techniques have been used to reconstruct magnetic islands in TEXTOR plasmas islands in TEXTOR plasmas

• I. Classen et al., PRL 98, 035001 (2007)

islands in TEXTOR plasmas. islands in TEXTOR plasmas. ECEI enables extraction of island parameters and helps to demonstrate ECEI enables extraction of island parameters and helps to demonstrate the effects of ECRH on these structures. the effects of ECRH on these structures.

Observation of ELMS with ECE-Imaging Observation of ELMS with ECE Imaging

ASDEX-U, Germany

J Boom Oct 29 2009

• J. Boom, Oct, 29, 2009

Simultaneous Imaging of LFS and HFS

Direct 2D visualization of core MHD perturbation structures Smaller amplitude perturbations (<10 eV) such Alfven eigenmodes b ibl t i b i t ti th ECEI i l ti may be possible to image by integrating the ECEI signal over time. Tearing mode structure at DIII-D

M A Van Zeeland et al Nucl Fusion 48 (2008) 092002

n=3 Toroidal Alfven Eigenmode

M A Van Zeeland et al PRL 97 135001 (2006) M.A. Van Zeeland et al, Nucl. Fusion 48 (2008) 092002 M.A. Van Zeeland et al, PRL 97, 135001 (2006)

Dual Dual-Array ECEI on DIII Array ECEI on DIII-D Dual Dual Array ECEI on DIII Array ECEI on DIII D

Waveguide outputs

Upper Pl tf

1 m

Waveguide outputs, Convex correctors Z O ti

Platform

Turning Mirror Beamsplitter LO Coupling Optics Zoom Optics Port Interface Focusing Optics Array Boxes

Lower Lower Platform

KSTAR ECEI View Window (B0=2.0 T) ( )

HFS

Low Field Side High Field Side

LFS

KSTAR ECEI System y

• II. Antenna Array
• I. Zoom/Focus Optics

+ III. Heterodyne Electronics

MIR system on KSTAR

Extensive test of the TEXTOR MIR system at POSTECH Laboratory test and the Gaussian beam analysis revealed phase- y y front curvature mismatch existed in the original TEXTOR MIR

• ptics

Optics will be revised to revisit the curvature matching issue

KSTAR MIR – (continued)

Lab tests using various reflecting targets including corrugated targets are under way to characterize the overall system performance. Density fluctuation information recovered from the KSTAR MIR together Density fluctuation information recovered from the KSTAR MIR together with the ECEI system will enable visualization of sawtooth crash in unprecedented detail. Ad d d t l i ( h bi t l l i t ) Advanced data analysis (cross-coherency, bi-spectral analysis, etc) techniques will provide further diagnostic information such as wave dispersion.

Reversal of poloidal rotation by NBI: Wave-dispersion recovered from MIR data (TEXTOR). Group velocity Vg

NBI On (co-injection) NBI Off

( ) p y

g

corresponds to the poloidal rotation

• velocity. Vg =+21km/s when NBI on

and Vg = -12km/s after NBI turned off

Summary

New generation of multi-dimensional plasma diagnostics

Visualization of the detailed reconnection physics by 2-D ECEI system

Reconnection physics is universal

Solar flare contains a similar “sawtooth oscillation” and the nature of the CME are similar to the reconnection process of the m=1 mode in tokamak

Comparative Study

Full reconnection model is consistent except no heat flow (no reconnection) before the pressure finger develops and the reconnection reconnection) before the pressure finger develops and the reconnection zone is toroidally localized Quasi-interchange model – Inconsistent with the measurement (magnetic instability is not likely a dominant mechanism) y y ) Ballooning mode model –”pressure finger” is consistent but crash pattern is not consistent with this model and global stochasticity of field lines may not be the dominant mechanism

Toroidal extent of the reconnection zone Toroidal extent of the reconnection zone

Kink motion (push to the low field side) is visible as the pressure builds up (#0 to #1) Hint of heat flow outside the inversion Hint of heat flow outside the inversion radius is in the later stage of precursors (frames 5 and 6) The reconnection is localized in the The reconnection is localized in the toroidal plane, the length is ~1/3 x 2πR0~360 cm Parallel heat diffusivity is important for y p heat transport

M3D simulation of the sawtooth crash on the TEXTOR verified the measured 2-D image of the wing of the hot spot (W. Park) g g p ( )

Observation of the crash at high field side (kink) g ( )

Kink type m/n=1/1 mode where no clear precursor R ti i l li d i Reconnection is localized in poloidal plane similar to the low field case A few attempts (pointed T A few attempts (pointed T

e

finger near the mid-plane) are made before the final puncture (#6 & #7) Reconnection starts with a small hole and it grows up to ~10 cm (#10) Heat flow is highly collective similar to the low field case Nested field line pushes the p heat out and island sets in (#11 and #12)

3-D localized random reconnection model

Crash direction has been

• bserved everywhere in high and

low field sides

Often m=1 mode moves toward the core (crash may have

• ccurred elsewhere (inward

arrows) arrows) Viewing window is 16 cm x 8 cm and the dimension of the poloidal hole is ~15 cm

The puncture size along the toroidal direction has to be finite (1/3 of the torus) (1/3 of the torus)

Helical structure (m/n=1/1) and

plasma rotation It will be rare to miss the ti if it h h li l

Arrow is the direction

• f the m=1 mode during

the crash time

reconnection if it has helical symmetry