1. Microwave Imaging and Visualization Diagnostics Developments for the Study of MHD and Microturbulence N.C. Luhmann, Jr. University of California at Davis Work performed in collaboration with I.G.J. Classen, C.W. Domier, A.J.H. Donné, R. Jaspers, X. Kong, T. Liang, A. Mase, T. Munsat, H.K. Park, Z. Shen, B.J. Tobias, M.J. van de Pol The First International Workshop on “Frontiers In Space and Fusion Energy Sciences (FISFES)", National Cheng Kung University (NCKU), Tainan, Taiwan, November 6-8, 2008 TEC

2. Energy Transport in High Temperature Toroidal Plasmas  Dynamics of high temperature plasmas in toroidal devices is complex –Transport physics –Empirical scaling –Magnetic islands, reconnection, transport barriers, turbulence, zonal flows, etc.  Need first principles based physics to successfully develop fusion energy –Advances in theoretical and computational understanding –Eliminate empirical scaling –Advanced diagnostics to connect the theoretical models to reliable scale-up ITER

3. Need to Measure Turbulent Fluctuations with Good Spatial and Temporal Resolution Important turbulence parameters for measurement - correlation length c - correlation time  c - density, potential, temperature fluctuation levels - velocity fluctuations (self regulation) Simple Random Walk Estimate: Diffusivity Outstanding questions in fusion science Is there a correlation between eddy size, fluctuation level and confinement? What controls the turbulent scale length in fusion plasmas? Small eddies Low transport Large eddies High transport c

4. Classical Fluids-Von Karmen Vortices

5. Electron Cyclotron Emission Imaging Microwave Imaging Reflectometry Collective Scattering Interferometry and Polarimetry Supporting MMW and THz Technology Areas UC Davis Millimeter Wave Plasma Diagnostics Program

6. Electron Cyclotron Emission (ECE) Electron gyromotion results in Electron Cyclotron Emission (ECE) at a series of discrete harmonic frequencies: ω n =nω ce In an optically thick plasma, the ECE radiation intensity is the black body intensity (Rayleigh-Jeans Region): In tokamak plasmas, there is a one to one mapping between frequency and radial position due to 1/R dependence of magnetic field B. ω ce  B  1/R ECE has become a standard technique to measure T e profiles and fluctuations in magnetic fusion plasmas B R ECE ω ce

7. In conventional 1-D ECE radiometry, a single antenna receives all frequencies. In ECEI, a vertically aligned antenna/ mixer array is employed as the receiver. Advantages: high spatial and temporal resolution, 2-D correlation. Real time 2-D imaging using wideband IF electronics and single sideband detection (16×8=128 channel system installed on TEXTOR; Two 24×48=1152 channel systems toroidally separated envisaged for KSTAR). Real time fluctuations can be studied down to ~1% level. 2-D ECE Imaging (ECEI)

8. Measures the electron temperature in 2D 2 nd harmonic X-mode ECE radiation intensity First 2D ECE Imaging diagnostic on TEXTOR very successful –8 x 16 observation volumes –High spatiotemporal resolution –Tuneable Detailed measurements of the 2D structure of instabilities ECE Imaging

9. Experimental TEXTOR setup for magnetic island heat transport study (left), and measured T e profile in this study as determined by Thomson scattering (right).

10. ECEI Applications Islands and NTMs ELMs Sawtooth crash H.K. Park et al. G.W. Spakman et al.

11. T e fluctuations Spatial resolution 1.5 cm in all directions; fluctuations must be larger Fluctuation amplitude generally much smaller than thermal noise level: 200 kHz sampling: 1.7% 1 MHz sampling: 3.7% 2 MHz sampling: 5.3% So: Correlation needed: only time averaged behavior survives The smaller the amplitude, the longer the needed integration time. 1s integration at 1MHz: noise level 0.1% Cross correlation between different ECEI channels in poloidal and radial directions.

12. Double Downconversion Approach (1) A characteristic frequency plot for the TEXTOR tokamak (B T =2.1 T) is shown left, showing 2nd and 3rd harmonic X-mode ECE spanning 94 GHz to >160 GHz Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1

13. Double Downconversion Approach (2) Quasi-optical notch filter prevents transmission of a narrow band of frequencies to protect against stray 140 GHz ECRH Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1

14. Double Downconversion Approach (3) Dichroic plate ensures single sideband operation: effect of f cutoff = 110 GHz plate shown left Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1

15. Double Downconversion Approach (4) Antennas receive broadband ECE, downconvert by f LO (at or near f cutoff ), and amplified by low noise amplifiers: example shows case of f LO =110 GHz combined with 2-20 GHz amplifiers Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1

16. Double Downconversion Approach (5) Downconverted 2-20 GHz signals are split into n bands and downconverted a second time by frequencies f LO1 through f LOn in the 2-8.4 GHz range: shown left are two such channels Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 f (GHz) 2.48.0

17. Double Downconversion Approach (6) Final step is to lowpass filter the n band signals, reducing the radial spot size and providing sharp band edges suitable for cross correlation studies Mixers Detectors Antennas Mixers LP Filters LO LO n Notch Filter ADCs Plasma Optics Dichroic Plate LO 1 f (GHz) 2.4 8.0

18. TEXTOR Study of “Sawtooth Oscillation” ECEI allows direct comparison between simulation and experimental data Time evolution of the island and m=1 mode based on the “full reconnection model” (Kadomtsev) agrees well with the measurement except the crash time H.K. Park et al., Physical Review Letters 96, 195003 (2006). H.K. Park et al., Physical Review Letters 96, 195004 (2006). H.K. Park et al., Physics of Plasmas 13, 055907 (2006). Everything.wmv

19. TEXTOR Study of “Sawtooth Oscillation” ECEI demonstrated “random 3-D reconnection zone,” in which the reconnection zone has been observed to occur everywhere (including high field side, see video left)

20. Magnetic Island Evolution under ECRH High power ECRH employed to suppress m/n = 2/1 tearing modes –Tearing modes induced by 1 kHz dynamic ergodic divertor (DED) –Modes suppressed by depositing 400 kW, 140 GHz ECRH on the same minor radius as tearing mode Tearing mode evolution observed by ECEI –Known DED frequency enables reconstruction –Time history mapped poloidally –Represents Low Field Side geometry One frame every rotation period (2 ms) Total movie length = 200 ms Classen, et al. “Effect of Heating in the Suppression of Tearing Modes in Tokamaks,” Physical Review Letters, 98, 2007.

21. Ongoing Advances: Next Generation ECEI Miniaturized substrate lens or mini-lens Front-side LO illumination New antennas with increased sensitivity and bandwidth New notch filters with enhanced ECRH rejection Vertical zoom capability Horizontal zoom capability

22. Filters Upper side bandLower side band LO 02.48-2.4-8 F [GHz] Different filter for each LO frequency: Remote controlled filter changer Dichroic plates for lower side band rejection Notch filter for 140 GHz ECRH protection -30 -25 -20 -15 -10 -5 0 110115120125130135140145 Transmission (dB) Frequency (GHz)

23. New Antennas and Array (air side) Measured LO Field Intensity Compared to the Mini-Lens Array ECEI Array Beamsplitter Notch Filters (3) New Tandem Notch Filters Next Generation ECEI

24. ECEI Array LO Source Zoom Control Lenses Focal Plane Translation Lens Beamsplitter New Mini-Lens ECEI System Optics Notch Filters (3)

25. Independent Vertical Zoom Experimental Verification Narrow Zoom Configuration is obtained providing minimum spot sizes and approximately 20 cm of total plasma coverage in the focal plane. In the Wide Zoom Configuration, coverage is increased to 33 cm. Spot sizes (2*w 0 ) in either transverse plane scale with plasma coverage, or image height (I). Depth of field (z R ) scales with the square of plasma coverage. Choice of focal plane position is independent of the zoom configuration! Vertical position relative to Tokamak Mid-Plane (mm) Tokamak Minor Radius (mm)

26. 50 cm Translation of Focal Position Demonstrated at 120 GHz in Wide Vertical Zoom Configuration Tokamak Minor Radius (mm)Vertical Position relative Tokamak Mid-Plane (mm)

27. New horizontal zoom capability via upgraded RF boards –RF spacing control, selectable between 500 and 900 MHz on a module-by-module basis –500 MHz spacing: 3.6–8.0 GHz coverage –900 MHz spacing: 2.0–9.2 GHz coverage New Horizontal Zoom Capability

28. TEXTOR: High and Low Field Composites

29. Demonstration of New “Zoom” Capability

30. The Future of ECEI is Bright! ECEI systems are installed and operating on TEXTOR, HT7, and LHD ECEI systems are envisaged for ASDEX-UG, DIII-D, KSTAR, EAST and HL-2M, with design and fabrication underway for many of these devices Capabilities of ECEI continue to grow in terms of both resolution and plasma coverage

31. ASDEX-UG TEXTOR system to transfer to ASDEX-UG in Jan. 2009 Initially employ TEXTOR array and electronics, to be replaced later with new horizontal zoom electronics

32. DIII-D System design and development have commenced Employ both horizontal and vertical zoom control with full remote capability Two array system –High field side, 100-130 GHz, 16×8 expandable to 16×24 –Low field side, 82-104 GHz, 16×8 expandable to 16×24 First results on DIII-D anticipated in Fall 2009

33. ECEI NOVA calculated T e perturbation for n=3 RSAE (left), and n=3 TAE (right) modes for DIII-D discharge 122117 [from M.A. Van Zeeland et al., PRL 97, 135001 (2006)]. Envisioned ECEI coverage is shown in yellow. T e perturbation amplitude (in eV) shown to right of each figure. Interference with 3rd harmonic ECE may limit viewing here DIII-D Coverage

34. Steady State Devices: KSTAR KSTAR system design under US-KSTAR collaboration program Initial 2 T operation: Two toroidally separated ECEI systems. Both with dual array configuration for simultaneous low and high field measurement capability –4x 1152 channels (3.0-3.5 T) operation: In-vacuum mirrors to minimize window area and heat load, and maximize coverage –Simultaneous ECEI and MIR ECEI (beams shown in red) employs 4 in-vacuum mirrors, with additional optics positioned outside the window

35. ECEI on KSTAR: Plasma Coverage Narrow zoom coverage Wide zoom coverage KSTAR Cassette Window

36. ECEI on KSTAR: Plasma Coverage Narrow zoom coverage Wide zoom coverage KSTAR Cassette Window Zoom control optics Translation stages

37. KSTAR ECEI: Top View Plasma Focal lenses Vacuum window Zoom lenses Beam splitter H plane lenses Cassette Low field array High field array Mirror

38. ECEI on ITER ?? Suggestion by Alan Costley at EC-15 to examine the possibility of employing the KSTAR mirror approach on ITER ECRH steering mirrors envisaged for ITER have sizes of 230 × 196 mm ECEI using similar sized mirrors may be possible

39. Need for Microwave Imaging Reflectometry (MIR)

40. 1-D fluctuations: straightforward interpretation 2-D fluctuations: Interference when observing beyond the diffraction distance Imaging can restore phase front! What is Microwave Imaging Reflectometry? Microwave reflectometry is a radar technique similar to ionospheric sounding, employed here for density fluctuation detection when

41. Effect of Fluctuations on 1-D Reflectometry Reflectometer signals (here TFTR) corrupted by interference from reflected wave components Power spectrum and amplitude distribution verify randomized interference pattern TFTR microwave signal phase plots E. Mazzucato, et al., Phys. Rev. Lett. 77, 15 (1996) Weak turbulence (clean signal) Strong turbulence burst (distorted signal) Spectral information lost for strong turbulence case

42. Microwave Imaging Reflectometry (MIR)  Probing beam illuminates extended region of cutoff layer  Curvature of the illuminating beam matched to that of the cutoff surface (toroidal and poloidal) for optical robustness  Cutoff layer imaged onto detector array (3 example points shown), eliminating the interference effects of multiple reflections  Detection system shares the same plasma-facing optics

43. Millimeter Wave Imaging Combined ECEI/MIR MIR System Configuration Combined ECEI/MIR System  The frequencies for ECEI and MIR systems are close but separable.  ECEI and MIR share same optics and window  They are separated by a dichroic plate TEXTOR Combined ECEI/MIR System ECEI and MIR share two front-end optics and window Mesh beamsplitter separates the ECEI and MIR signals Dual dipole antenna arrays are used for both ECEI and MIR ECEI/MIR optics are designed to minimize image spot size

44. Video Amps IF Amp I-Q Mixer Antenna Mixer Filters LO DACs Plasma Optics Beam Splitter Toroidal Mirror Window MIR Array LO Source Illumination Source Plasma Poloidal Mirror MIR Electronics MIR - System Overview

45. Characterization of MIR system Known corrugated reflectors used to characterize complete MIR system response to range of k  and  n/n, and to compare performance of 1-D and imaging techniques Surface corrugation precisely measured with Leica “Laser Tracker” visible interferometer, used as reference for measurements

46. Test results of MIR system (laboratory) Blue curve is measured reference k  = 1.25 cm -1   2  ( ñ/n  0.3%) 1-D System d=10 cm 1-D System d=30 cm Imaging System d at image focus 1-D system correlation near unity for d<20 cm, decorrelated as d~30 cm MIR system near unity in focal range, falls off beyond ‘depth of field’ Amplitude modulation suppressed near focus in both systems

47. Analytic model (1-D system) precisely duplicates data

48. into focus back out of focus TEXTOR Quadrature (I-Q) Signals unfocused spectrum focused spectrum Complex field amplitude from the prototype TEXTOR MIR system as the cutoff layer is swept through the focal plane of the imaging optics. out of focus Initial TEXTOR MIR Results

49. Multichannel TEXTOR MIR Data

50. Further lab tests of MIR system for robust operation MIR system has been applied to the plasma measurement –Curvature matching condition from plasma cut-off layer is not as sharp as expected from infinite conductivity assumption of modeling –Correlation length based on phase information is not consistent with that based on amplitude of reflected waves (inherent conventional reflectometry problem) MIR system sent to POSTECH to understand the issues that we learned from plasma application –Fundamental difference between plasma cut-off and perfect reflector: dielectric multi-layer reflector versus metal surface. –Doppler reflectometry shares the same fundamental problem of the conventional reflectometry. Extensive laboratory tests will be conducted with simulation study –1.5D and/or 3D EM simulation (PPPL) will be compared with laboratory test to clarify the outstanding issues.

51. Multi-frequency Illumination for 2-D turbulence A simultaneous “comb” of illumination frequencies can probe multiple cutoff layers, as each distinct frequency reflects from a distinct cutoff layer Measurement of multi-layer turbulence flow such as “zonal flow” in the core of tokamak plasma

52. Schematic illustration of the principles governing Doppler reflectometry

53. 2-D simulations of microwaves reflected from a circular plasma, with an illumination beam curvature-matched to the plasma applicable to MIR and synthetic imaging

54. Zonal flow 2-D reflectometer (57-61 GHz) simulations of a circular plasma with imposed poloidal flow velocity marked by solid lines.

55. Thank You for Your Attention