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

Results of MSE and CXRS imaging in KSTAR John Howard, Clive Michael, Alex Thorman, Peter Urlings (ANU) Jinil Chung (NFRI) 1

Overview of talk • 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 2

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 p s p Doppler shift J. Ko, J. Chung, A.G.G. Lange and M.F.M. de Bock, 2013 JINST 8 C10022 Injected beam atoms feel Induced electric field in frame of the beam E = v x B  Splitting of H a and Doppler shift  p and s components are orthogonally polarized. s is parallel to ( v x B) so orientation gives pitch angle of B  Wideband filter and interferometer allows imaging polarimetry of B z (r,z) 4

IMSE observes the full multiplet For the p multiplet components the interferometer output is: S p = I p [1+ z p cos( f p + 2 q )] For the orthogonal s components ( q+p/2, slightly different wavelength): S s = I s [1- z s cos( f s + 2 q )] (note sign change) For MSE triplet, add the interferograms and choose optical delay t to maximize the contrast difference z p – z s Left : model MSE spectrum showing the orthogonally polarized central s and outer p components Righ t: The associated interferometric fringe contrast versus optical delay for s, p and nett. 5

IMSE view is 9 o above midplane KSTAR Image: M. F. M. De Bock etal, Review of Scientific Instruments 83, 10D524 (2012) 6

The KSTAR Optical system is inserted into the port cassette Optical cell Switching hybrid system Sensicam CCD camera (lead box Optical rail not shown) 400 mm achromatic lens Retractable F-mount lens telescope (300mm x 135mm) reference polarizer Front lens (-80 mm) and dielectric mirror 7

Hybrid system has high radial resolution Combined spatial and temporal modulation • Frame 1 q q q • No beam, radiation unpolarized  no interference fringes S = I [1+ z cos(ky+ f+ 2 q )] • Frame 2 Difference phase 4 q S = I [1+ z cos(ky+ f- 2 q )]

Measured and modelled Doppler phase Measurement Model • The fixed phase f depends on the energy-dependent Doppler shift of the multiplet: S = I [1+ z cos(ky+ f+ 2 q )] • 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

Imaging MSE application to equilibrium estimation IMSE reveals internal current profile details Vertical field Bz (EFIT) Vertical field Bz (IMSE) MSE uses EFIT Y (r,z) EFIT (Contours) LCFS as Axis position (EFIT) boundary condition Presently IMSE equilibria are valid only under Axis position (IMSE) single beam based on dBz/dz = 0 injection Y (r,z) IMSE (Colour fill) conditions

Study of type I ELM #9033 Imaging MSE reveals edge pedestal dynamics Radius (m) Edge pedestal current Before ELM Beam modulations Halpha Radius (m) During ELM Combine Imaging MSE and Imaging Inferred Bz maps. Note: potential CXRS  possibly help distinguish Er and contribution from Er Bz in edge

#9033 Bz and dBz/dr (~jTor) profiles Bz image Bz profile During ELM Bz EFIT Uncertainty here (2 beams overlap) Pre-ELM During ELM Averaging window dBz/dr image “Current density” During ELM Pre-ELM During ELM

ECCD modulation experiments • 170GHz 2 nd 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 Using bottom 170GHz launcher YS Bae et al Fus Sci Tech, 59, 640 (2010) 13

ECCD current drive experiments IMSE measurements Polarization angle evolution Stored energy Axis position (EFIT) IMSE EFIT Axis position (IMSE) based Agree about total current but on dBz/dz = 0 differ about profile details No Shafranov shift

EFIT q profile and ECE temperature measurements and general observations IMSE q-profile ECE Bz perturbation During ECCD: • q profile broadens (based on IMSE central slice EFIT), • Sawteeth suppressed during ECCD pulse • Little or no Shafranov shift Fractional change in beam emission intensity also shows electron heating. ( D-alpha emission coefficient decreases with increasing % beam intensity perturbation electron temperature. Anderson et al , Plasma Phys. Control. Fusion 42 (2000) 781 – 806 ) 15

ECCD modulation experiments Measured current density spatio-temporal response (10 cycle average) Axis Bz small here – possible systematic error 16

ECCD perturbation evolution: Bz (top) and its radial derivative (below) Possible artifact (low Bz) ECCD Current shifts to inside Edge skin current 17

ECCD modulation experiments Edge skin current ECCD pulse Time constant ~ 50 ms Pulse-length-averaged deposition profile FWHM ~ 4cm Current moves inside – induction effect? 18

The multiple beam problem 19

Multiple beams  complex spectra J. Ko, J. Chung, A.G.G. Lange and M.F.M. de Bock, 2013 JINST 8 C10022 20

How to manage? Conventional polarimetric system: Use just a single polarized component of 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) Spectroscopic approach: fit the spectrum. Difficult, time consuming, uncertainties J. Ko, J. Chung, A.G.G. Lange and M.F.M. de Bock, 2013 JINST 8 C10022 21

What about the imaging system? The image is: S = I [1+ z cos(kx + f +/- 2 q )] For a single beam, the polarization angle is proportional to the vertical field: q ~ g B z The interferometric phase f depends on beam Doppler shift When superimposing beams we must add the Stokes vectors  2 q = ( I 1 q 1 + I 2 q 2 )/( I 1 +I 2 ) The net interferometric phase f gives the relative beam intensities  I 1 / I 2 Camera pixel B z (R 1 ,Z 1 ) B z (R 2 ,Z 2 ) Assume toroidal symmetry B z (R,Z, f) = B z (R,Z). Solve matrix equation for B z In the case of 3 beams, we can use the fringe contrast z as an additional constraint 22

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, or use of half/third energy components • Develop real time IMSE for AT and long pulse control 23

Overview of talk • 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 24

CXRS imaging considerations for KSTAR #7266 Time=5.355 sec Radius=2250 m 16000 Measured Intensity 14000 BG CX 12000 Filter*Gaussian 10000 Total spectrum Intensity [a.u.] 8000 Active CXRS 6000 Passive emission 4000 Background 2000 0 Figure courtesy Dr Ko and Mr Lee -2000 527 527.5 528 528.5 529 529.5 530 530.5 Wavelength [nm] Fourier transform 7 unknowns: A 4-carrier coherence imaging system Background gives 9 pieces of information – Passive: brightness, width and offset sufficient to reconstruct the CVI Active: brightness, width and offset 529nm CXRS spectrum. 25

Use multiple simultaneous spatial heterodyne carriers to encode coherence at multiple delays k x- -k y k x +k y k x k y + + + = Plasma image Fourier transform showing carriers Reflections 26

Example images – not yet analysed #7320 - Ohmic phase start-up #7320 – Beams on Note fringe distortion and Sharp fringes  loss of contrast  hot! cold Use start-up fringes to Plasma LCFS estimate instrument function

Example KSTAR CXRS imaging data CXRS system views both beams simultaneously. Expect carrier phases and contrasts to be inconsistent. H mode transition at 4s Inferred “flows” at 4 independent delays Need to be processed to obtain true Doppler shifts for active component. 28

“Flow” and “ion temperature” images Uncalibrated, unregistered and uninverted data at a single delay 3.90s 3.96s 4.02s 4.08s 4.14s Transient edge Ti ridge ? Ion temperature color scale max ~3keV L-H transition 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) SNR needs to be improved … Camera exposures 29

2014: 4 quadrant imaging CXRS 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 30