Analysis of the HAE activity in the TJ-II stellarator using a Landau closure model Articles uri icon

authors

  • ORTIZ LUENGO, JUAN
  • VARELA RODRIGUEZ, JACOBO
  • Herrera Quesada, L.
  • Pons Villalonga, P.
  • Cappa, A.
  • Losada, U.
  • Papoušek, F.
  • van Milligen, B. Ph
  • GARCIA GONZALO, LUIS
  • Spong, D. A.
  • Ghai, Y.
  • Ochando, M. A.
  • Hidalgo, C.

publication date

  • July 2025

issue

  • 7, 072506

volume

  • 32

International Standard Serial Number (ISSN)

  • 1070-664X

Electronic International Standard Serial Number (EISSN)

  • 1089-7674

abstract

  • The aim of this study is to analyze the stability of helical Alfvén eigenmodes (HAEs) in TJ-II discharges and the stabilizing effect of the energetic particles generated by the neutral beam injector (NBI) on pressure gradient-driven modes (PGDMs). HAE and PGDM stability is studied using the linear version of the gyro-fluid code FAR3d and the continuous structure by the STELLGAP code. First, Alfvén eigenmode (AE) and PGDM activity observed in the experiments is reproduced by the simulations, identifying unstable
    and
    HAEs triggered around
    showing a frequency of 209 and 204 kHz, respectively, as well as
    PGDM. Next, a parametric study is performed with respect to the thermal ion density and iota profile in the middle-outer plasma region to verify the robustness of the simulation results with respect to the uncertainty of experimental profiles. The analysis confirms that experimental uncertainty does not cause large deviations in the simulation results, showing the destabilization of the same HAEs for all the configurations tested. The simulations also indicate the decay of the
    PGDM growth rate as the energetic particle (EP) population in the plasma increases, consistent with the experiment. Stability analysis of the
    ⁠,
    ⁠,
    ⁠, and
    helical families is performed with respect to the NBI operational regime for different EP energies,
    as well as deposition profiles. The most unstable configuration is the radially localized on-axis NBI operation (stiff EP density profile gradients nearby the magnetic axis). Using the simulation model that reproduces the observed Alfvén activity, we extend the study to analyze NBI performance within a theoretical framework. It shows that increasing NBI voltage (which raises EP energy) leads to a degradation in NBI performance for a given power (related to EP
    and their density). To achieve better NBI operation, higher voltage must be balanced with lower injection power, ensuring stable AEs while keeping the same EP
    ⁠.

subjects

  • Physics

keywords

  • spectrograms; thomson scattering; plasma confinement; plasma diagnostics; plasma heating; plasma instabilities; plasma properties and parameters; plasma waves; stellarators; tokamaks.