Visualization Technique for MHD and Visualization Technique for MHD - PowerPoint PPT Presentation

Visualization Technique for MHD and Visualization Technique for MHD and Transport Physics in tokamaks Hyeon K. Park Physics Department POSTECH Pohang, Korea at 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 T e and n e 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 Conventional 1-D ECE system 2-D ECE imaging system � ECE measurement is an established tool for electron temperature � 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 � T e 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 Initial agreement with the full reconnection model is excellent Quasi-reconnection model

Comparison with the ballooning mode model Low Field Side 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”) ( 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. High Field Side � Diff � 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 The LO coupling beamsplitter is re The LO coupling beamsplitter is re- -located located � ECE signal within the array box within the array box No wasted power, no LO beam dump No wasted power, no LO beam dump � Even and odd channels are separated for Even and odd channels are separated for � Dichroic Plate more relaxed vertical spacing, but imaged to more relaxed vertical spacing, but imaged to (High Pass Filter) the same plane the same plane Filtered ECE Beamsplitter Beamsplitter IF Even frequency Odd Channel Local Mini-lens Array, y, Channel Channel Oscillator Even Channels Mini-Lens Mini-Lens Array Array IF frequency Beamsplitter Mini-lens Array, Odd Channels Signal g LO

Improved Video Electronics Improved Video Electronics 2.5 � Highly linear video response to Highly linear video response to 2 temperature fluctuations up to temperature fluctuations up to 1.5 50% 50% 50% 50% 1 � Video BW variable from 12.5 to Video BW variable from 12.5 to 0.5 Volts 400 kHz and compatible with 400 kHz and compatible with 0 ± 2.5 V digital acquisition 2.5 V digital acquisition -0.5 -1 � Proprietary designs developed Measured Response Proprietary designs developed -1.5 and tested at UC Davis and tested at UC Davis and tested at UC Davis and tested at UC Davis Linear Fit -2 -1 -0.5 0 0.5 1 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 2.082992 s t=2.0847422 s t 2.0847422 s

Intermittent Reconnection Process Intermittent Reconnection Process

Intermittent Reconnection Process Intermittent Reconnection Process High Field Side Low Field Side First reconnection is First reconnection is not complete not complete First crash is toward First crash is away top top from this view from this view Remnants of m=1 Remnants of m=1 mode survives for 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 I. Classen et al., PRL 98, 035001 (2007) � 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 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 may be possible to image by integrating the ECEI signal over time. b ibl t i b i t ti th ECEI i l ti Tearing mode structure at DIII-D n=3 Toroidal Alfven Eigenmode M A Van Zeeland et al Nucl Fusion 48 (2008) 092002 M.A. Van Zeeland et al, Nucl. Fusion 48 (2008) 092002 M A Van Zeeland et al PRL 97 135001 (2006) M.A. Van Zeeland et al, PRL 97, 135001 (2006)

Dual Dual Dual Array ECEI on DIII Dual-Array ECEI on DIII Array ECEI on DIII-D Array ECEI on DIII D 1 m Upper Waveguide outputs Waveguide outputs, Pl tf Platform Turning Mirror Convex correctors Beamsplitter Zoom Optics Z O ti LO Coupling Optics Port Interface Focusing Optics Array Boxes Lower Lower Platform

KSTAR ECEI View Window (B 0 =2.0 T) ) LFS HFS 0 ( Low Field Side High Field Side

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 optics � 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 � Advanced data analysis (cross-coherency, bi-spectral analysis, etc) d d t l i ( h bi t l l i t ) techniques will provide further diagnostic information such as wave dispersion . Reversal of poloidal rotation by NBI: NBI On NBI Off Wave-dispersion recovered from MIR (co-injection) data (TEXTOR). Group velocity V g ( ) p y g corresponds to the poloidal rotation velocity. V g =+21km/s when NBI on and V g = -12km/s after NBI turned off