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Title: Second harmonic electron cyclotron pre-ionization in the DIII-D tokamak

Authors:
; ; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1170894
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Fusion; Journal Volume: 47; Journal Issue: 4
Country of Publication:
United States
Language:
English

Citation Formats

G.L,Jackson, J.S,deGrassie, C.P,Moeller, and R,Prater. Second harmonic electron cyclotron pre-ionization in the DIII-D tokamak. United States: N. p., 2007. Web. doi:10.1088/0029-5515/47/4/003.
G.L,Jackson, J.S,deGrassie, C.P,Moeller, & R,Prater. Second harmonic electron cyclotron pre-ionization in the DIII-D tokamak. United States. doi:10.1088/0029-5515/47/4/003.
G.L,Jackson, J.S,deGrassie, C.P,Moeller, and R,Prater. Sun . "Second harmonic electron cyclotron pre-ionization in the DIII-D tokamak". United States. doi:10.1088/0029-5515/47/4/003.
@article{osti_1170894,
title = {Second harmonic electron cyclotron pre-ionization in the DIII-D tokamak},
author = {G.L,Jackson and J.S,deGrassie and C.P,Moeller and R,Prater},
abstractNote = {},
doi = {10.1088/0029-5515/47/4/003},
journal = {Nuclear Fusion},
number = 4,
volume = 47,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}
  • In many high-performance discharges in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. {bold 8}, 441 (1985)] high electron density prevents determining the electron temperature from the second harmonic electron cyclotron emission (ECE). A technique for obtaining central electron temperatures from optically gray third harmonic ECE is presented that does not require knowledge of the reflective properties of the vessel wall. The temperature values derived from ECE spectra measured with an absolutely calibrated Michelson interferometer agree with independent measurements by Thomson scattering. As part of this work, a method of determining the optical depth of thirdmore » harmonic frequencies in a low aspect ratio tokamak is also demonstrated. The optical depth measurements are in agreement with calculations correct to first order in the Larmor radius. {copyright} {ital 1996 American Institute of Physics.}« less
  • Cutoff of microwave emission at the second harmonic of the electron cyclotron frequency has been used to infer the local electron density profile in the DIII-D tokamak. Modeling the density profile during the uncontrolled density increase associated with the transition to H-mode operation permits the profile shape factor and line average to be estimated. In special cases, the density fluctuations associated with sawteeth can also be inferred. Independent corroboration of the standard density diagnostics has been performed with this technique.
  • Experiments simulating the ITER Baseline Scenario on the DIII-D tokamak show that torque-free pure electron heating, when coupled to plasmas subject to a net co-current beam torque, affects density fluctuations at electron scales on a sub-confinement time scale, whereas fluctuations at ion scales change only after profiles have evolved to a new stationary state. Modifications to the density fluctuations measured by the Phase Contrast Imaging diagnostic (PCI) are assessed by analyzing the time evolution following the switch-off of Electron Cyclotron Heating (ECH), thus going from mixed beam/ECH to pure neutral beam heating at fixed β N . Within 20 msmore » after turning off ECH, the intensity of fluctuations is observed to increase at frequencies higher than 200 kHz; in contrast, fluctuations at lower frequency are seen to decrease in intensity on a longer time scale, after other equilibrium quantities have evolved. Non-linear gyro-kinetic modeling at ion and electron scales scales suggest that, while the low frequency response of the diagnostic is consistent with the dominant ITG modes being weakened by the slow-time increase in flow shear, the high frequency response is due to prompt changes to the electron temperature profile that enhance electron modes and generate a larger heat flux and an inward particle pinch. Furthermore, these results suggest that electron heated regimes in ITER will feature multi-scale fluctuations that might affect fusion performance via modifications to profiles.« less
    Cited by 1
  • Experiments simulating the ITER Baseline Scenario on the DIII-D tokamak show that torque-free pure electron heating, when coupled to plasmas subject to a net co-current beam torque, affects density fluctuations at electron scales on a sub confinement time scale, whereas fluctuations at ion scales change only after profiles have evolved to a new stationary state. Modifications to the density fluctuations measured by the Phase Contrast Imaging diagnostic (PCI) are assessed by analyzing the time evolution following the switch-off of Electron Cyclotron Heating (ECH), thus going from mixed beam/ECH to pure neutral beam heating at fixed βN. Within 20ms after turningmore » off ECH, the intensity of fluctuations is observed to increase at frequencies higher than 200 kHz; in contrast, fluctuations at lower frequency are seen to decrease in intensity on a longer time scale, after other equilibrium quantities have evolved. Non-linear gyro-kinetic modeling at ion and electron scales scales suggest that, while the low frequency response of the diagnostic is consistent with the dominant ITG modes being weakened by the slow-time increase in flow shear, the high frequency response is due to prompt changes to the electron temperature profile that enhance electron modes and generate a larger heat flux and an inward particle pinch. These results suggest that electron heated regimes in ITER will feature multi-scale fluctuations that might affect fusion performance via modifications to profiles.« less
    Cited by 1