Results of MSE and CXRS imaging in KSTAR John Howard, Clive Michael, - - PowerPoint PPT Presentation

John Howard, Clive Michael, Alex Thorman, Peter Urlings (ANU) Jinil Chung (NFRI)

Results of MSE and CXRS imaging in KSTAR

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Overview of talk

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• Imaging MSE systems for current tomography

and Er

• IMSE capabilities for estimating equilibrium
• Pedestal studies
• ECCD modulation
• Future challenges, new capabilities and 2014 plans
• Passive Doppler Coherence Imaging Systems
• MAST Divertor imaging
• KSTAR CXRS imaging
• 2014 plans

Why do MSE and Doppler imaging ?

• At least two orders of magnitude more measurements

(pixels)

• Imaging with fast cameras gives temporal and spatial

resolution ~5ms and ~1 cm

• Suitable for studying plasma asymmetries, structures and

for current profile control

– Divertors – RMP perturbations, – sawteeth and MHD – ECCD, LHCD, NBCD etc.

Analyzing MSE spectra

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Injected beam atoms feel Induced electric field in frame of the beam E = v x B Splitting of Ha and Doppler shift  p and s components are orthogonally polarized. s is parallel to (v x B) so

• rientation gives pitch angle of B

Wideband filter and interferometer allows imaging polarimetry of Bz(r,z) p p s Doppler shift

• J. Ko, J. Chung, A.G.G. Lange and M.F.M. de Bock, 2013 JINST 8 C10022

IMSE observes the full multiplet

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For the p multiplet components the interferometer output is: Sp = Ip [1+zp cos(fp+2q)] For the orthogonal s components (q+p/2, slightly different wavelength): Ss = Is [1-zs cos(fs+2q)] (note sign change) For MSE triplet, add the interferograms and choose optical delay t to maximize the contrast difference zp – zs

Left: model MSE spectrum showing the

• rthogonally polarized

central s and outer p components Right: The associated interferometric fringe contrast versus optical delay for s, p and nett.

IMSE view is 9o above midplane

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KSTAR Image: M. F. M. De Bock etal, Review of Scientific Instruments 83, 10D524 (2012)

The KSTAR Optical system is inserted into the port cassette

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Front lens (-80 mm) and dielectric mirror 400 mm achromatic lens F-mount lens telescope (300mm x 135mm) Optical cell Sensicam CCD camera (lead box not shown) Optical rail Retractable reference polarizer Switching hybrid system

Hybrid system has high radial resolution

Frame 1 Frame 2

• q

q q

• Combined spatial and temporal modulation

S = I [1+z cos(ky+f+2q)] S = I [1+z cos(ky+f-2q)]

No beam, radiation unpolarized  no interference fringes

Difference phase 4q

Measured and modelled Doppler phase

• The fixed phase f depends on the energy-dependent Doppler

shift of the multiplet: S = I [1+z cos(ky+f+2q)]

• IMSE system tolerant to a wide range of beam energies
• The nett Doppler phase image can be used to obtain the

relative beam emission intensities in dual beam injection case  Should allow recovery of poloidal field

Measurement Model

Imaging MSE application to equilibrium estimation

Axis position (IMSE) based on dBz/dz = 0 Axis position (EFIT)

Y(r,z) IMSE (Colour fill) Y(r,z) EFIT (Contours) Vertical field Bz (EFIT) Vertical field Bz (IMSE)

MSE uses EFIT LCFS as boundary condition Presently IMSE equilibria are valid only under single beam injection conditions

IMSE reveals internal current profile details

Study of type I ELM #9033 Imaging MSE reveals edge pedestal dynamics

Edge pedestal current Beam modulations Halpha

Before ELM During ELM

Inferred Bz maps. Note: potential contribution from Er Combine Imaging MSE and Imaging CXRS  possibly help distinguish Er and Bz in edge Radius (m) Radius (m)

#9033 Bz and dBz/dr (~jTor) profiles

Bz EFIT

“Current density”

During ELM During ELM

Bz profile

Averaging window

Uncertainty here (2 beams overlap)

Bz image

During ELM

dBz/dr image

During ELM Pre-ELM Pre-ELM

ECCD modulation experiments

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• 170GHz 2nd harmonic injection at 20 deg toroidal
• ECCD modulation commences at start of Ip flat top
• 2Hz modulation, 10 cycles
• Camera acquires 20 frames per cycle
• The final 8 cycles are averaged
• “Zero”-ECCD frame is subtracted from sequence

YS Bae et al Fus Sci Tech, 59, 640 (2010)

Using bottom 170GHz launcher

ECCD current drive experiments IMSE measurements

Stored energy Polarization angle evolution Axis position (IMSE) based

• n dBz/dz = 0

Axis position (EFIT)

EFIT IMSE

Agree about total current but differ about profile details

No Shafranov shift

EFIT q profile and ECE temperature measurements and general observations

15 During ECCD:

• q profile broadens (based on IMSE central slice EFIT),
• Sawteeth suppressed during ECCD pulse
• Little or no Shafranov shift

IMSE q-profile

Fractional change in beam emission intensity also shows electron heating. (D-alpha emission coefficient decreases with increasing

electron temperature. Anderson et al, Plasma Phys.

• Control. Fusion 42 (2000) 781–806 )

ECE Bz perturbation

% beam intensity perturbation

Measured current density spatio-temporal response (10 cycle average) Axis

ECCD modulation experiments

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Bz small here – possible systematic error

ECCD perturbation evolution: Bz (top) and its radial derivative (below)

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ECCD Possible artifact (low Bz) Current shifts to inside Edge skin current

ECCD modulation experiments

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Time constant ~ 50 ms Pulse-length-averaged deposition profile FWHM ~ 4cm

Edge skin current ECCD pulse Current moves inside – induction effect?

The multiple beam problem

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Multiple beams  complex spectra

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• J. Ko, J. Chung, A.G.G. Lange and M.F.M. de Bock, 2013 JINST 8 C10022

How to manage?

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Conventional polarimetric system: Use just a single polarized component

• f the light. Very
• challenging. Low light
• M. F. M. De Bock, D. Aussems, R. Huijgen, M. Scheffer and J. Chung, Review of Scientific Instruments 83, 10D524 (2012)
• J. Ko, J. Chung, A.G.G. Lange and M.F.M. de Bock, 2013 JINST 8 C10022

Spectroscopic approach: fit the

• spectrum. Difficult,

time consuming, uncertainties

What about the imaging system?

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The image is: S = I [1+z cos(kx + f +/- 2q)] For a single beam, the polarization angle is proportional to the vertical field: q ~ g Bz The interferometric phase f depends on beam Doppler shift When superimposing beams we must add the Stokes vectors  2q = (I1q1 + I2q2 )/(I1+I2 ) The net interferometric phase f gives the relative beam intensities  I1 / I2 Camera pixel

Bz(R1,Z1) Bz(R2,Z2)

Assume toroidal symmetry Bz(R,Z,f) = Bz(R,Z). Solve matrix equation for Bz In the case of 3 beams, we can use the fringe contrast z as an additional constraint

Next steps

• Demonstrate operation in presence of dual

beams

• Confirm quantum mechanical modeling of Stark-

Zeeman polarization (ellipticity)

• Estimation of Er using combined Li/MSE beams,
• r use of half/third energy components
• Develop real time IMSE for AT and long pulse

control

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Overview of talk

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• Imaging MSE systems for current tomography and Er
• IMSE capabilities for estimating equilibrium
• Pedestal studies
• ECCD modulation
• Future challenges, new capabilities and 2014 plans
• Passive Doppler Coherence Imaging Systems
• MAST Divertor imaging
• KSTAR CXRS imaging
• 2014 plans

CXRS imaging considerations for KSTAR

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527 527.5 528 528.5 529 529.5 530 530.5

• 2000

2000 4000 6000 8000 10000 12000 14000 16000 #7266 Time=5.355 sec Radius=2250 m Wavelength [nm] Intensity [a.u.] Measured Intensity BG CX Filter*Gaussian

Total spectrum Active CXRS Passive emission Background

Figure courtesy Dr Ko and Mr Lee

7 unknowns: Background Passive: brightness, width and offset Active: brightness, width and offset

A 4-carrier coherence imaging system gives 9 pieces of information – sufficient to reconstruct the CVI 529nm CXRS spectrum.

Fourier transform

Use multiple simultaneous spatial heterodyne carriers to encode coherence at multiple delays

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ky

+ + +

kx kx--ky kx+ky

Plasma image

=

Fourier transform showing carriers Reflections

Example images – not yet analysed

#7320 - Ohmic phase start-up #7320 – Beams on

Note fringe distortion and loss of contrast  hot! Plasma LCFS Sharp fringes  cold

Use start-up fringes to estimate instrument function

Example KSTAR CXRS imaging data

28 H mode transition at 4s

CXRS system views both beams

• simultaneously. Expect carrier phases and

contrasts to be inconsistent. Inferred “flows” at 4 independent delays Need to be processed to obtain true Doppler shifts for active component.

“Flow” and “ion temperature” images

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Uncalibrated, unregistered and uninverted data at a single delay 3.96s 4.02s 4.08s 4.14s 3.90s Transient edge Ti ridge ?

Ion temperature color scale max ~3keV Ion flow color scale max ~150 km/s Apparent radial displacement of ion flow and Ti peaks during H phase (but data not unfolded yet)

Camera exposures L-H transition

SNR needs to be improved …

2014: 4 quadrant imaging CXRS

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4 quadrant image of test target With carrier fringes superimposed

Crossed Wollaston prisms produce 4 identical images Horizontal fringe pattern ensures maximum radial resolution Image plane “quad delay plate” gives 4 different samples of the interferogram

Quad delay plate

Conclusion and outlook

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 Imaging spectro-polarimeters utilizing spatial heterodyne encoding can encode both Doppler and full Stokes information  IMSE significantly increases the information available to directly infer or constrain the current profile.  Next step: simultaneous high radial resolution imaging CXRS and MSE (KSTAR 2014)

• Dual beam MSE operations
• Resolving contribution of Er
• Synchronous imaging of MHD and ELMs
• Systematic study of effects of RMP pedestal control
• Loop voltage imaging for AT current profile control

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Doppler spatial heterodyne imaging

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Angle-dependent path difference  Generates carrier fringe pattern in focal plane when E an O waves interfere through a polarizer

Polarizer

A birefringent displacer separates the E and O rays

Interferogram: S = I [1+z cos(Kxx + f)]

A carrier wave Kx on the image can encode Doppler phase f (related to plasma flow)

Phase = center wavelength  plasma flow Contrast = line width temperature With correct cut angle, a single plate can suffice. A section of the interferogram is then imaged

• nto the CCD camera

Motivation for SOL and divertor imaging: Complex physics requiring sophisticated modeling

SOL/Divertor used to exhaust helium ash, impurities, manage waste heat load. Flow patterns are not well understood: multiple sources and sinks

• B-independent sources: In-out diffusion asymmetry,

plasma detachment

• B-dependent sources: Grad B drifts, ExB, grad p
• Divertor sink: retention, recycling, radiative cooling etc

Experimental validation of modeling is required. Present edge flow measurement diagnostics include:

• Doppler spectroscopy - small number of chords, poor

spatial resolution

• Mach probe - Intrusive and of limited spatial reach or

coverage

Asakura etal, J. Nucl. Mat. (2007)

First validation of edge codes on DIII-D

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40 Km/s 20 1.1 1.2 1.3 1.4 R (m) 1.5 1.6 1.7 –20 –0.8 Z (m) –0.9 –1.0 –1.1 –1.2 –1.3 –40 40 Km/s 20 1.1 1.2 1.3 1.4 R (m) 1.5 1.6 1.7 –20 –0.8 Z (m) –0.9 –1.0 –1.1 –1.2 –1.3 –40

UEDGE Calculation

Shot 142613, 4500ms

Divertor flow reconstructions obtained on DIIID in 2010. Good comparison with edge modeling codes. Upgraded systems coming online:

• Upper and lower divertor and midplane views (wider angles, higher throughput,

time resolution to ~1ms)

• Passively thermally stabilized optics – potentially requiring a once off calibration

CIII 465nm Measurement

First CIII 465nm Doppler SOL flow imaging on MAST

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• Counter-propagating

flows at early times

• Up/down asymmetry

at later times

82 ms 202 ms 250 ms 290 ms

Still from wide angle viewing system Scott Silburn & MAST team

CIII Divertor flow tomography

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L mode H mode Reconstructions of C2+ flow Scott Silburn & MAST team

• Simulations of eps, psi using equilibrium field and Bz
• Exptl Doppler results with beam overlap
• Next steps – double/triple beam
• Half/third energies?
• Synchronous imaging
• Real time IMSE
• Li beam?
• Use beam into gas shots 9328,9329 to compare different

beams

• Calibration analysis

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Notes/ to do Total driven current (internal) Loop voltage images

For discussion

• Optical fiber (imaging)
• New camera coffin
• New viewing window
• Internal blackening
• Fiducials for I port
• What is integrated current density in
• ECCD. Cf loop voltage

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Why do imaging MSE?

• Technical advantages:

– Simple inexpensive instrument - Wideband filter, no tuning issues or incidence angle sensitivities – Higher light efficiency – Multiple heterodyne options, temporal or spatial, single channel or imaging

• Insensitive to broadband polarized background
• Can self-consistently measure beam velocity vector distribution (Doppler

shifts)

• Tolerant of beam energy changes / beam tilt
• Seems insensitive to Stark-Zeeman coupling
• Image context shows problem areas (reflections etc)
• Self-calibrating (image points are connected)
• Possibility to use Zeeman Halpha for optics polarization response

(captured within FoV)

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Solving diffusion equation

Non-inductive Current drive

=   

2

/ 1 . r f B E

• Current diffusion equation is solved:
• Only perturbed part is considered here, and temperature is kept constant (change in

temperature lowers total loop voltage on timescale of electron heating).

• A “back-reaction current” flows in direction opposite to driven current to keep total

current constant. The 1D perturbed current flux diffusion equation is solved subject to constant current boundary condition and shows time/spatial evolution of current inside and outside driven layer:

Non-inductive current Source region Back-current flows adjacent to current layer Clive Michael

Image processing

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Thresh = 200 Thresh = 100

ToDo

• Iterative solution of MSE equation
• Improve estimation of flux surfaces
• Loop voltage imaging

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q=0 q0 Hybrid spatio-temporal heterodyne systems  Single carrier fringe pattern for y or e Phase difference between consecutive frames gives q Better radial resolution but requires two frames

f+2y

• f+2y

2e

q=45o q=22.5o Spatial heterodyne systems  Multiple carrier fringe patterns encode angles

Multiple spectro-polarimetric approaches

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ECCD “current” perturbation evolution

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ECCD off ECCD starts time Possible artifact

Next KSTAR campaign: Synchronous imaging of MHD

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4/3 4/3 5/4 5/4 6/5 7/6 6/5 5/4

Configuration parameter kh

Rotational transform scan Projections of synchronously imaged Alfven activity in the H-1 heliac Phase flip about the resonance