Formation and detection of internal transport barriers in low-current tokamaks

T. Kurki-Suonio, S. Lashkul, Jukka Heikkinen

Research output: Contribution to journalArticleScientificpeer-review

15 Citations (Scopus)

Abstract

In low-current tokamaks, in the absence of radial electric fields (Er), the widths of the drift orbits are large and the direct orbit losses can extend deep into the plasma. Furthermore, in such a plasma even a modest Er can produce rotation with a poloidal Mach number (Mp) that exceeds unity. Using the Monte Carlo code ASCOT, which follows charged particle orbits in the five-dimensional phase space, the formation of an internal transport barrier (ITB) in such a tokamak is investigated. Carrying out the simulations for the geometry corresponding to the FT-2 tokamak, it is shown that if, under these conditions, a steep density gradient is created in the plasma, the plasma responds by generating a strong (much stronger than needed to compensate the diamagnetic drift) Er in the region of the strong gradient. The generation appears to be a pure neoclassical effect, but a global solution over the entire plasma cross section is required to fully identify it. As a result, an ITB-like situation with a strongly sheared E*B flow is obtained inside the plasma. In these circumstances Mp>1, and thus the orbits of the majority of ions become strongly squeezed. The neutral fluxes observed by neutral particle analysers are also simulated to find out if the neutral spectra can be utilized to estimate the Er values across the plasma cross section in the FT-2 tokamak.
Original languageEnglish
Pages (from-to)301-323
JournalPlasma Physics and Controlled Fusion
Volume44
Issue number3
DOIs
Publication statusPublished - 2002
MoE publication typeA1 Journal article-refereed

Fingerprint

low currents
Plasmas
Orbits
orbits
gradients
cross sections
neutral particles
Charged particles
Mach number
unity
charged particles
Electric fields
Fluxes
Geometry
electric fields
Ions
estimates
geometry
ions
simulation

Keywords

  • plasma
  • fusion energy
  • fusion reactors
  • tokamak
  • internal transport barriers
  • cross sections

Cite this

Kurki-Suonio, T. ; Lashkul, S. ; Heikkinen, Jukka. / Formation and detection of internal transport barriers in low-current tokamaks. In: Plasma Physics and Controlled Fusion. 2002 ; Vol. 44, No. 3. pp. 301-323.
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Formation and detection of internal transport barriers in low-current tokamaks. / Kurki-Suonio, T.; Lashkul, S.; Heikkinen, Jukka.

In: Plasma Physics and Controlled Fusion, Vol. 44, No. 3, 2002, p. 301-323.

Research output: Contribution to journalArticleScientificpeer-review

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AU - Heikkinen, Jukka

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N2 - In low-current tokamaks, in the absence of radial electric fields (Er), the widths of the drift orbits are large and the direct orbit losses can extend deep into the plasma. Furthermore, in such a plasma even a modest Er can produce rotation with a poloidal Mach number (Mp) that exceeds unity. Using the Monte Carlo code ASCOT, which follows charged particle orbits in the five-dimensional phase space, the formation of an internal transport barrier (ITB) in such a tokamak is investigated. Carrying out the simulations for the geometry corresponding to the FT-2 tokamak, it is shown that if, under these conditions, a steep density gradient is created in the plasma, the plasma responds by generating a strong (much stronger than needed to compensate the diamagnetic drift) Er in the region of the strong gradient. The generation appears to be a pure neoclassical effect, but a global solution over the entire plasma cross section is required to fully identify it. As a result, an ITB-like situation with a strongly sheared E*B flow is obtained inside the plasma. In these circumstances Mp>1, and thus the orbits of the majority of ions become strongly squeezed. The neutral fluxes observed by neutral particle analysers are also simulated to find out if the neutral spectra can be utilized to estimate the Er values across the plasma cross section in the FT-2 tokamak.

AB - In low-current tokamaks, in the absence of radial electric fields (Er), the widths of the drift orbits are large and the direct orbit losses can extend deep into the plasma. Furthermore, in such a plasma even a modest Er can produce rotation with a poloidal Mach number (Mp) that exceeds unity. Using the Monte Carlo code ASCOT, which follows charged particle orbits in the five-dimensional phase space, the formation of an internal transport barrier (ITB) in such a tokamak is investigated. Carrying out the simulations for the geometry corresponding to the FT-2 tokamak, it is shown that if, under these conditions, a steep density gradient is created in the plasma, the plasma responds by generating a strong (much stronger than needed to compensate the diamagnetic drift) Er in the region of the strong gradient. The generation appears to be a pure neoclassical effect, but a global solution over the entire plasma cross section is required to fully identify it. As a result, an ITB-like situation with a strongly sheared E*B flow is obtained inside the plasma. In these circumstances Mp>1, and thus the orbits of the majority of ions become strongly squeezed. The neutral fluxes observed by neutral particle analysers are also simulated to find out if the neutral spectra can be utilized to estimate the Er values across the plasma cross section in the FT-2 tokamak.

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