Chapter 3: Internal transport barrier studies in the FTU

E. Barbato, V. Pericoli-Ridolfini, C. Castaldo, B. Esposito, E. Giovannozzi, C. Gormezano, G. Granucci, M. Leigheb, M. Marinucci, F. Mirizzi, L. Panaccione, S. Podda, M. Romanelli, P. Smeulders, C. Sozzi

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Abstract

Strong electron internal transport barriers (ITBs) are obtained in the Frascati Tokamak Upgrade (FTU) with the combined injection of lower hybrid (LH) (up to 1.9 MW) and electron cyclotron (EC) (up to 0.8 MW) radio-frequency waves. ITBs occur during either the current plateau or the ramp-up phase, both in full and partial current drive (CD) regimes, up to ne0> 1.4 × 1020m-3, relevant to ITER operation. Central electron temperatures Te0> 8 keV, at ne0≈ 0.8 × 1020m-3, are sustained for up to 36 confinement times. The ITB extends over a region where a slightly reversed magnetic shear is established by off-axis LHCD and can be even larger than r/a = 0.5. EC power is used either to benefit from this improved confinement by heating inside the ITB or to enhance the peripheral LH power deposition and CD with off-axis resonance. Collisional ion heating is also observed, but thermal equilibrium with the electrons is not attained since the electron-ion equipartition time is always 4 to 5 times longer than the energy confinement time. An extensive transport modeling of these discharges, performed by means of the ASTRA code, is also presented. During the ITB phase, the ion diffusivity is close to the neoclassical value while the electron shear-dependent Bohm-gyro-Bohm model accounts quite well for Te(r, t), The Ray Tracing Fokker-Planck model, used to describe the LHCD physics, appears satisfactory to analyze and interpret the experimental results. It turns out that the barrier radius is mainly influenced by the LHCD deposition. In particular, a wider barrier is obtained the lower qais and the larger the plasma density is.
Original languageEnglish
Pages (from-to)323 - 338
Number of pages16
JournalFusion Science and Technology
Volume45
Issue number3
DOIs
Publication statusPublished - 2004
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Civil and Structural Engineering
  • Nuclear and High Energy Physics
  • Nuclear Energy and Engineering
  • Materials Science(all)
  • Mechanical Engineering

Cite this

Barbato, E., Pericoli-Ridolfini, V., Castaldo, C., Esposito, B., Giovannozzi, E., Gormezano, C., ... Sozzi, C. (2004). Chapter 3: Internal transport barrier studies in the FTU. Fusion Science and Technology, 45(3), 323 - 338. https://doi.org/10.13182/FST04-A517