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Title: Experimental and modeling uncertainties in the validation of lower hybrid current drive

Abstract

Our work discusses sources of uncertainty in the validation of lower hybrid wave current drive simulations against experiments, by evolving self-consistently the magnetic equilibrium and the heating and current drive profiles, calculated with a combined toroidal ray tracing code and 3D Fokker–Planck solver. The simulations indicate a complex interplay of elements, where uncertainties in the input plasma parameters, in the models and in the transport solver combine and compensate each other, at times. It is concluded that ray-tracing calculations should include a realistic representation of the density and temperature in the region between the confined plasma and the wall, which is especially important in regimes where the LH waves are weakly damped and undergo multiple reflections from the plasma boundary. Uncertainties introduced in the processing of diagnostic data as well as uncertainties introduced by model approximations are assessed. We show that, by comparing the evolution of the plasma parameters in self-consistent simulations with available data, inconsistencies can be identified and limitations in the models or in the experimental data assessed.

Authors:
 [1];  [2];  [2];  [2];  [2];  [2];  [1];  [1];  [1];  [1];  [3];  [3];  [4];  [2];  [2];  [2];  [2]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
  3. CompX, Del Mar, CA (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1338617
Grant/Contract Number:
AC02-CH0911466; FC02-99ER54512
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 9; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; lower hybrid waves; tokamak; validation; hard x-rays; integrated modeling

Citation Formats

Poli, F. M., Bonoli, P. T., Chilenski, M., Mumgaard, R., Shiraiwa, S., Wallace, G. M., Andre, R., Delgado-Aparicio, L., Scott, S., Wilson, J. R., Harvey, R. W., Petrov, Yu V., Reinke, M., Faust, I., Granetz, R., Hughes, J., and Rice, J. Experimental and modeling uncertainties in the validation of lower hybrid current drive. United States: N. p., 2016. Web. doi:10.1088/0741-3335/58/9/095001.
Poli, F. M., Bonoli, P. T., Chilenski, M., Mumgaard, R., Shiraiwa, S., Wallace, G. M., Andre, R., Delgado-Aparicio, L., Scott, S., Wilson, J. R., Harvey, R. W., Petrov, Yu V., Reinke, M., Faust, I., Granetz, R., Hughes, J., & Rice, J. Experimental and modeling uncertainties in the validation of lower hybrid current drive. United States. doi:10.1088/0741-3335/58/9/095001.
Poli, F. M., Bonoli, P. T., Chilenski, M., Mumgaard, R., Shiraiwa, S., Wallace, G. M., Andre, R., Delgado-Aparicio, L., Scott, S., Wilson, J. R., Harvey, R. W., Petrov, Yu V., Reinke, M., Faust, I., Granetz, R., Hughes, J., and Rice, J. 2016. "Experimental and modeling uncertainties in the validation of lower hybrid current drive". United States. doi:10.1088/0741-3335/58/9/095001. https://www.osti.gov/servlets/purl/1338617.
@article{osti_1338617,
title = {Experimental and modeling uncertainties in the validation of lower hybrid current drive},
author = {Poli, F. M. and Bonoli, P. T. and Chilenski, M. and Mumgaard, R. and Shiraiwa, S. and Wallace, G. M. and Andre, R. and Delgado-Aparicio, L. and Scott, S. and Wilson, J. R. and Harvey, R. W. and Petrov, Yu V. and Reinke, M. and Faust, I. and Granetz, R. and Hughes, J. and Rice, J.},
abstractNote = {Our work discusses sources of uncertainty in the validation of lower hybrid wave current drive simulations against experiments, by evolving self-consistently the magnetic equilibrium and the heating and current drive profiles, calculated with a combined toroidal ray tracing code and 3D Fokker–Planck solver. The simulations indicate a complex interplay of elements, where uncertainties in the input plasma parameters, in the models and in the transport solver combine and compensate each other, at times. It is concluded that ray-tracing calculations should include a realistic representation of the density and temperature in the region between the confined plasma and the wall, which is especially important in regimes where the LH waves are weakly damped and undergo multiple reflections from the plasma boundary. Uncertainties introduced in the processing of diagnostic data as well as uncertainties introduced by model approximations are assessed. We show that, by comparing the evolution of the plasma parameters in self-consistent simulations with available data, inconsistencies can be identified and limitations in the models or in the experimental data assessed.},
doi = {10.1088/0741-3335/58/9/095001},
journal = {Plasma Physics and Controlled Fusion},
number = 9,
volume = 58,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
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  • The generation of currents in toroidal plasma by application of waves in the lower hybrid frequency range involves the interplay of several physical phenomena which include: wave propagation in toroidal geometry, absorption via wave-particle resonances, the quasilinear generation of strongly nonequilibrium electron and ion distribution functions, and the self-consistent evolution of the current density in such a nonequilibrium plasma. We describe a code, LHMOD, which we have developed to treat these aspects of current drive and heating in tokamaks. We present results obtained by applying the code to a computation of current ramp-up and to an investigation of the possiblemore » importance of minority hydrogen absorption in a deuterium plasma as the ''density limit'' to current drive is approached. copyright 1987 Academic Press, Inc.« less
  • Using ray tracing, a detailed investigation of the lower-hybrid (LH) wave propagation in presence of toroidal magnetic field ripple is presented. The local ray behavior is first depicted for a cylindrical equilibrium periodically modulated along the axial direction. Variations along ray trajectories in the component of the wave vector parallel to the equilibrium magnetic field are observed, with a maximum relative amplitude that is locally of the order of the ripple level. For the full rippled toroidal equilibrium, a similar local behavior is found when the ray trajectory crosses a high ripple region. Despite the modest amplitude of the localmore » ray perturbation, its global influence on ray trajectories may be strong, as a consequence of the combined effects of toroidal and poloidal inhomogeneities. By coupling ray tracing with a one-dimensional relativistic Fokker-Planck code, simulations of LH experiments have been performed for the TORE SUPRA tokamak [Equipe TORE SUPRA, in {ital Proceedings of the 15{sup th} Conference on Plasma Physics and Controlled Nuclear Fusion Research}, Seville (International Atomic Energy Agency, Vienna, 1995), Vol. 1, p. 105, Paper IAEA-CN-60/A1-5]. It is shown that magnetic ripple may induce significant modifications in the LH power deposition profiles, mainly in the {open_quote}{open_quote}few passes{close_quote}{close_quote} regime when the wave makes some, but not many, passes inside the plasma before being absorbed. The effect of magnetic ripple leads then to a broadening of the power deposition profile and a shift towards the center of the plasma, and a better coupling with high energy electrons. This behavior may be explained by an increase in the overall ray stochasticity. Taking into account magnetic ripple in LH simulations, a better agreement is found between numerical predictions and experimental observations. {copyright} {ital 1996 American Institute of Physics.}« less
  • A detailed investigation is presented on the ability of combined ray-tracing and Fokker--Planck calculations to predict the hard x-ray (HXR) emission during lower-hybrid (LH) current drive in tokamaks when toroidally induced ray stochasticity is important. A large number of rays is used and the electron distribution function is obtained by self-consistently iterating the appropriate power deposition and Fokker--Planck calculations. It is shown that effects due to radial diffusion of suprathermal electrons and to radiation scattering by the inner wall can be significant. The experimentally observed features of the HXR emission are fairly well predicted, thus confirming that combined ray-tracing andmore » Fokker--Planck codes are capable of correctly modeling the physics of LH current drive in tokamaks.« less
  • The Lower Hybrid current drive (LHCD) modeling is revisited in the light of the recently proposed scheme involving only few rays [l]. Besides the strong reduction of the computational effort, this approach allows to recover a physical meaning for the spectral width associated with each ray, while the quasilinear selfconsistency may be fully achieved. Three examples are presented for ITER, C-MOD and Tore Supra tokamaks to illustrate the effectiveness of the method, which cover most of the LHCD regimes found in this type of machines.