Abstract
This paper presents new measurements of the crossphase angle, , between longwavelength density, , and electron temperature,, fluctuations in the core of DIIID [J. L. Luxon, Nucl. Fusion42, 614 (2002)] tokamak plasmas. The coherency and crossphase angle between and are measured using coupled reflectometer and correlation electron cyclotron emission diagnostics that view the same plasma volume. In addition to the experimental results, two sets of local, nonlinear gyrokinetic turbulence simulations that are performed with the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys.186, 545 (2003)] are described. One set, called the preexperiment simulations, was performed prior to the experiment in order to predict a change in given experimentally realizable increases in the electron temperature,. In the experiment the crossphase angle was measured at three radial locations (, 0.65, and 0.75) in both a “Base” case and a “High ” case. The measured crossphase angle is in good qualitative agreement with the preexperiment simulations, which predicted that and would be out of phase. The preexperiment simulations also predicted a decrease in crossphase angle as is increased. Experimentally, this trend is observed at the inner two radial locations only. The second set of simulations, the postexperiment simulations, is carried out using local parameters taken from measured experimental profiles as input to GYRO. These postexperiment simulation results are in good quantitative agreement with the measured crossphase angle, despite disagreements with transport fluxes. Directions for future modeling and experimental work are discussed.
This research was supported by the U.S. Department of Energy under Grant Nos. DEAC0506OR23100, DEFG0308ER54984, DEFG0207ER54917, DEFG0395ER54309, and DEFC0204ER54698. The research of A.E.W. was performed under an appointment to a DOE ORISE FES postdoctoral fellowship. J.C.H. is supported by a DOE ORISE FES graduate fellowship. A.E.W. wishes to thank the tokamak operators for this experiment, J. R. Ferron and B. Hudson, and would like to acknowledge insightful input from D. Mikkelson and R. Prater. A.E.W. also thanks R. J. Groebner for CER analysis and C. Holcomb for MSE analysis. We thank the entire DIIID team for their support of these experiments. The GYRO simulations reported here were performed on FRANKLIN at NERSC.
I. INTRODUCTION
II. PREEXPERIMENT GYRO SIMULATIONS
III. COUPLED REFLECTOMETRY AND CECE DIAGNOSTICS
IV. EXPERIMENTAL RESULTS
V. INITIAL POSTEXPERIMENT GYRO SIMULATIONS
VI. SUMMARY OF RESULTS AND DIRECTIONS FOR FUTURE WORK
Key Topics
 Turbulent flows
 71.0
 Plasma diagnostics
 53.0
 Reflectometers
 51.0
 Turbulence measurement
 41.0
 Plasma turbulence
 28.0
Figures
The wave number spectrum of at calculated from nonlinear GYRO simulations shows the decrease in cross phase as is increased by 50%. Values of at plotted vs percent change in . Linear GYRO runs (blue circles) and nonlinear GYRO runs (red diamonds) show good agreement both for the magnitude of the crossphase angle and the trend with increasing .
The wave number spectrum of at calculated from nonlinear GYRO simulations shows the decrease in cross phase as is increased by 50%. Values of at plotted vs percent change in . Linear GYRO runs (blue circles) and nonlinear GYRO runs (red diamonds) show good agreement both for the magnitude of the crossphase angle and the trend with increasing .
Diagram of coupled CECE and reflectometer diagnostics at DIIID. The inset shows profiles of plasma frequencies with example values of and where CECE and reflectometer radial measurement locations will overlap.
Diagram of coupled CECE and reflectometer diagnostics at DIIID. The inset shows profiles of plasma frequencies with example values of and where CECE and reflectometer radial measurement locations will overlap.
Example of measured correlated long wavelength and in a plasma with only Ohmic heating and ECH (no beams) at DIIID (133 626, , ). (a) The power spectrum of density fluctuations measured with the scattered power signal from the reflectometer, (b) the power spectrum of electron temperature fluctuations measured with CECE using a twochannel correlation technique, (c) the coherency spectrum of density and electron temperature fluctuations, and (d) the crossphase angle spectrum between density and electron temperature fluctuations.
Example of measured correlated long wavelength and in a plasma with only Ohmic heating and ECH (no beams) at DIIID (133 626, , ). (a) The power spectrum of density fluctuations measured with the scattered power signal from the reflectometer, (b) the power spectrum of electron temperature fluctuations measured with CECE using a twochannel correlation technique, (c) the coherency spectrum of density and electron temperature fluctuations, and (d) the crossphase angle spectrum between density and electron temperature fluctuations.
Measured plasma profiles comparing reference shots with NBI only (black) and a shot with NBI and ECH (redgrey), corresponding to a “Base” case and “High ” case, respectively. Data from 138 038 (redgrey) and 138 040 (black), are shown.
Measured plasma profiles comparing reference shots with NBI only (black) and a shot with NBI and ECH (redgrey), corresponding to a “Base” case and “High ” case, respectively. Data from 138 038 (redgrey) and 138 040 (black), are shown.
Changes in linear stability of the ITG mode and TEM calculated using TGLF comparing reference shots 138 040 and 138 038 corresponding to a “Base” case (black) and “High ” case (redgrey), respectively. Results at in 138 038 (redgrey) and 138 040 (black) at are shown.
Changes in linear stability of the ITG mode and TEM calculated using TGLF comparing reference shots 138 040 and 138 038 corresponding to a “Base” case (black) and “High ” case (redgrey), respectively. Results at in 138 038 (redgrey) and 138 040 (black) at are shown.
Changes in transport as calculated using ONETWO comparing a “Base” case (black) and a “High ” case (redgrey). Experimental profiles from reference shots 138 038 and 138 040 at were used as input to ONETWO. Dashed lines indicate a onesigma standard deviation resulting from random uncertainties in the input profiles.
Changes in transport as calculated using ONETWO comparing a “Base” case (black) and a “High ” case (redgrey). Experimental profiles from reference shots 138 038 and 138 040 at were used as input to ONETWO. Dashed lines indicate a onesigma standard deviation resulting from random uncertainties in the input profiles.
The measured coherency, , and crossphase angle, , comparing “Base” cases (black) and “High ” cases (redgrey) are shown at three radial locations. At and 0.65 smaller crossphase angles are measured in the High Case. At there is no change in crossphase angle outside experimental error bars. Horizontal dashed lines on the coherency plot indicates a statistical noise limit, error bars on the crossphase angle are the onesigma standard deviations, and a horizontal line at is plotted for reference.
The measured coherency, , and crossphase angle, , comparing “Base” cases (black) and “High ” cases (redgrey) are shown at three radial locations. At and 0.65 smaller crossphase angles are measured in the High Case. At there is no change in crossphase angle outside experimental error bars. Horizontal dashed lines on the coherency plot indicates a statistical noise limit, error bars on the crossphase angle are the onesigma standard deviations, and a horizontal line at is plotted for reference.
The “Base” case (black) and the “High” case (redgrey) crossphase angles measured at three radial locations. The plotted values are the average crossphase angle in the frequency range , the errors bars are the onesigma standard deviation on the frequency averaged crossphase angle.
The “Base” case (black) and the “High” case (redgrey) crossphase angles measured at three radial locations. The plotted values are the average crossphase angle in the frequency range , the errors bars are the onesigma standard deviation on the frequency averaged crossphase angle.
The measured changes in long wavelength electron temperature and density fluctuation levels measured with CECE and BES, respectively. The electron temperature fluctuation level is obtained by integrating the CECE crosspower spectrum between and longwavelength density fluctuation level is obtained by integrating the BES crosspower spectrum between . Error bars represent the experimental uncertainty in the measurements.
The measured changes in long wavelength electron temperature and density fluctuation levels measured with CECE and BES, respectively. The electron temperature fluctuation level is obtained by integrating the CECE crosspower spectrum between and longwavelength density fluctuation level is obtained by integrating the BES crosspower spectrum between . Error bars represent the experimental uncertainty in the measurements.
Comparison of experimental results at to postexperimental simulation results using the local parameters from 138 038, as input. (a) The GYRO unfiltered (blacksolid), synthetic diagnostic (bluedashed), and experimental (redgrey) crosspower spectra have been normalized to compare the spectral shape. (b) The GYRO unfiltered (blacksolid), synthetic diagnostic (bluedashed), and experimental crossphase angles (redgrey) are compared. The onesigma standard deviations are plotted as error bars at each frequency in (a) and (b). Note that the experimental phase angle is meaningfully compared with the simulations only where it is resolved (frequencies where the coherency is high), between . Outside this frequency range the measured is in the noise.
Comparison of experimental results at to postexperimental simulation results using the local parameters from 138 038, as input. (a) The GYRO unfiltered (blacksolid), synthetic diagnostic (bluedashed), and experimental (redgrey) crosspower spectra have been normalized to compare the spectral shape. (b) The GYRO unfiltered (blacksolid), synthetic diagnostic (bluedashed), and experimental crossphase angles (redgrey) are compared. The onesigma standard deviations are plotted as error bars at each frequency in (a) and (b). Note that the experimental phase angle is meaningfully compared with the simulations only where it is resolved (frequencies where the coherency is high), between . Outside this frequency range the measured is in the noise.
The sample volumes for the synthetic CECE and reflectometer signals are separated by and the radial separation, , is scanned. The crossphase angle is shown in (a) and the coherency is shown (b).
The sample volumes for the synthetic CECE and reflectometer signals are separated by and the radial separation, , is scanned. The crossphase angle is shown in (a) and the coherency is shown (b).
The sample volumes for the synthetic CECE and reflectometer signals are separated by and the vertical separation, , is scanned. The crossphase angle is shown in (a) and the coherency is shown in (b).
The sample volumes for the synthetic CECE and reflectometer signals are separated by and the vertical separation, , is scanned. The crossphase angle is shown in (a) and the coherency is shown in (b).
Tables
Local parameters at midradius used in two preexperiment GYRO simulations. The “Base” case parameters are from DIIID discharge 128 913, , . For the “High ” case the input electron temperature to GYRO has been increased 50%.
Local parameters at midradius used in two preexperiment GYRO simulations. The “Base” case parameters are from DIIID discharge 128 913, , . For the “High ” case the input electron temperature to GYRO has been increased 50%.
Results from the preexperiment set of local, nonlinear GYRO simulations comparing transport and turbulence at for the “Base” and “High ” cases. Statistical errors are 1% for turbulence levels and 2%–3% for transport levels.
Results from the preexperiment set of local, nonlinear GYRO simulations comparing transport and turbulence at for the “Base” and “High ” cases. Statistical errors are 1% for turbulence levels and 2%–3% for transport levels.
Local parameters at from reference discharges 138 040 and 138 038 at , corresponding to an experimental “Base” case and “High ” case, respectively. These are used as inputs for the postexperiment GYRO simulations.
Local parameters at from reference discharges 138 040 and 138 038 at , corresponding to an experimental “Base” case and “High ” case, respectively. These are used as inputs for the postexperiment GYRO simulations.
Postexperiment GYRO simulations from 138 038, , . Turbulence amplitudes and cross phase are compared with synthetic diagnostic results.
Postexperiment GYRO simulations from 138 038, , . Turbulence amplitudes and cross phase are compared with synthetic diagnostic results.
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