Bridging the spectral gap in lower hybrid current drive by parametric instability

R. Cesario, C. Castaldo, A. Cardinali, F. Paoletti

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Abstract

A broadening of the radiofrequency (RF) power spectrum coupled to tokamak plasma is necessary to occur in order to explain the existing experiments of lower hybrid current drive (LHCD). The presented modeling shows that the parametric instability (PI) driven by ion sound quasi-modes produces in the scrape-off-plasma an important contribution to such spectral broadening. As effect of the quasi-linear interaction of the resulting LH spectrum penetrating in the bulk, the LH power fraction deposited in the plasma at the first pass results enhanced. Consequently, well defined LH deposition profiles are obtained when the ray propagation in toroidal geometry is taken into account. Considering the parameters of LHCD experiments of JET (Joint European Torus), and other machines as well, the PI growth rate is high enough for compensating the convective losses and broadening a fraction (≈10%) of the launched power spectrum. The LH spectral broadening is intrinsic to coupling RF power in LHCD experiments, and increases operating with higher plasma densities. As principal implication of such spectral broadening, experiments able evidencing the effects of a well-defined LH deposition profile, as those characterized by high electron temperature in the core and broad profile, are successfully interpreted. Useful experiments are the LHCD-sustained internal transport barriers of JET. The design of scenarios relevant to the modern fusion research program, which require the control of the plasma current profile in the outer half of plasma, can be properly achieved by considering the physics of the plasma edge for modeling the LH deposition profile and the q-profile evolution. © 2005 American Institute of Physics.
Original languageEnglish
DOIs
Publication statusPublished - 26 Sep 2005
Externally publishedYes
EventRADIO FREQUENCY POWER IN PLASMAS: 16th Topical Conference on Radio Frequency Power in Plasmas - , United States
Duration: 26 Sep 2005 → …

Conference

ConferenceRADIO FREQUENCY POWER IN PLASMAS: 16th Topical Conference on Radio Frequency Power in Plasmas
CountryUnited States
Period26/9/05 → …

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All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

Cesario, R., Castaldo, C., Cardinali, A., & Paoletti, F. (2005). Bridging the spectral gap in lower hybrid current drive by parametric instability. Paper presented at RADIO FREQUENCY POWER IN PLASMAS: 16th Topical Conference on Radio Frequency Power in Plasmas, United States. https://doi.org/10.1063/1.2098243