Excitation of toroidal Alfvén eigenmodes with counter-current NBI in the TCV tokamak

Vallar, M.; Dreval, M.; García-Muñoz, M.; Sharapov, S. E.; Poley, Jesús; Karpushov, A.; Lauber, Philipp; Mazzi, S.; Porte, L.

doi:10.1088/1741-4326/acb644

Cited by 5 publications

(13 citation statements)

References 25 publications

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“…Lastly, at JET, NBI-driven modes were observed during injection of tritium beams into a tritium plasma and during the injection of deuterium beams into a deuterium plasma at a low toroidal magnetic field in dedicated experiments at a low magnetic field [25]. NBI-driven AEs were subsequently observed on many other tokamaks such as HL-2A [26], AUG [27], and more recently, on TCV [28]. On the other hand, numerical studies have evidenced that 1-MeV tangential beams in ITER can also destabilize AEs, particularly when beam deposition is dominantly off-axis to reduce the stabilizing influence of thermal plasma ions [29].…”

Section: Introductionmentioning

confidence: 94%

Predictive modeling of Alfvén eigenmode stability in inductive scenarios in JT-60SA

Coelho,

Vincenzi,

Vallar

et al. 2023

Front. Phys.

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The JT-60SA device offers unique conditions before ITER for the study of the interaction of energetic particles with plasma waves. With similar dimensions to JET, e.g., a major radius but with a slightly more elongated plasma volume, JT-60SA is used as a high-power device where additional heating power (including 10 MW of the 500 keV Neutral Beam Injection) of up to 41 MW and the potential for high non-inductive plasma current operation pave the path for numerous challenges in physics on MHD stability, in particular, when considering the effects of energetic particles. Several operational scenarios with ITER and DEMO-relevant plasma regimes, in terms of non-dimensional plasma parameters, are anticipated. In this work, the stability of Alfvén eigenmodes (AEs) in variants of two of the most relevant operational scenarios with single null is analyzed: a full Ip inductive scenario at high density (1.1 × 1020 m−3 on-axis electron density) and 5.48MA/2.05T toroidal plasma current and magnetic field, and an advanced (hybrid) scenario with an ion energy transport barrier (ITB) and 3.5MA/2.28T toroidal plasma current and magnetic field. The workflow included the CRONOS code to establish the scenario, the ASCOT code to calculate the slowing-down energetic particle distributions for a positive/negative ion source-based neutral beam, and the MISHKA/CASTOR-K suite to calculate the MHD spectra of AEs and the associated drive/damping contributions from the NBI energetic ions, as well as the thermal ion landau damping. The systematic analysis, over a large Fourier space of the toroidal mode number/mode frequency, provides evidence that although a significant fraction of supra-Alfvénic particles stemming from the negative ion source-based neutral beam (500 keV) can, in some cases, drive to AEs in both scenarios, it is not enough to overcome the thermal ion landau damping. In addition, the advanced scenario with ITB is shown to be stable against AEs localized in the vicinity of the barrier as well, offering good prospects of sustainability of the plasma performance and of ITB. Finally, some sensitivity scan results are shown on the influence of fast ion density and q-profile on the AE mode spectra and stability.

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Section: Introductionmentioning

confidence: 94%

Predictive modeling of Alfvén eigenmode stability in inductive scenarios in JT-60SA

Coelho,

Vincenzi,

Vallar

et al. 2023

Front. Phys.

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“…When only a single n = 1, 95 kHz TAE mode is observed, as in the case of #72101, the MHD spectroscopy approach is not applicable for f rot determination in this discharge. The maximum estimated velocity of toroidal rotation of −100 km s −1 [7] introduces the toroidal rotation frequency of f rot = −18 kHz.…”

Section: Mishka Calculation Of Tae Eigenfunctionsmentioning

confidence: 99%

“…Beam-driven TAEs and energeticparticle-induced geodesic acoustic modes were then observed during NBI heating on TCV [6]. In particular, a variety of high amplitude MHD modes in the frequency range up to 600 kHz were recently seen in TCV discharges with counter-current NBI [7]. The low frequency fraction of these modes is clearly seen by SXR cameras in addition to the magnetic diagnostics.…”

Section: Introductionmentioning

confidence: 97%

Determination of MHD mode structures using soft x-ray diagnostics in TCV

Dreval¹,

Sharapov²,

Vallar³

et al. 2023

Plasma Phys. Control. Fusion

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A forward modeling technique is developed for determining the characteristic features of observed MHD modes from the line-of-sight data of the soft X-ray (SXR) diagnostics with 64 vertical lines-of- sights in the TCV tokamak. This technique with the use of the diagnostics with excellent spatial resolution is shown to evaluate the poloidal mode numbers m, radial location and ballooning character of the MHD modes. At the first stage the poloidal mode structures have been modeled by the radially localized Gaussian-shaped emission regions rotating along the magnetic flux surfaces. At the second stage, the space structures of observed 95-100 kHz toroidal Alfvén eigenmodes (TAEs) are investigated numerically using HELENA, CSCAS and MISHKA codes. The calculated TAE eigenfunctions are used then in our forward modeling similarly to the approach of contrast imaging diagnostics [Edlund E M et al 2009 Phys. Rev. Lett. 102 165003] and SXR diagnostics [Piovesan P et al 2008 Nucl. Fusion 48 065001]. A ballooning structure of the observed n=1 TAE mode can be analyzed more easily due to the low poloidal mode number m in contrast to the high m modes analyzed by similar SXR technique in W7-X stellarator [M B Dreval et al 2021 Plasma Phys. Control. Fusion 63 065006].

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“…As mentioned previously, the developed scenario has been previously described in Ref. [21], but for the sake of clarity, the main characteristics of such a scenario are presented in the following.…”

Section: Description Of Experimental Setupmentioning

confidence: 99%

“…For these reasons, the Tokamak à Configuration Variable (TCV) [18] represents a suitable test-bed case for studying the impact of fast-ion-driven AEs on the turbulence properties and transport characteristics. Indeed, recent efforts through the efficient exploitation of the tangential neutral beam injectors (NBIs) [19] allowed the development of plasma scenarios with a rich variety of unstable AEs [20,21]. In particular, TAEs have been routinely observed in such scenarios, offering the possibility to compare with the studies at JET [11].…”

Section: Introductionmentioning

confidence: 99%

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

Mazzi,

Vallar,

Kumar

et al. 2023

Front. Phys.

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Following recent observations of unstable Toroidal Alfvén Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and performance is carried out. The study shows experimental evidence of non-degradation of ion thermal confinement despite the increasing of auxiliary power. During such an improved confinement period, Toroidal Alfvén Eigenmodes (TAEs) driven by fast ions generated through Neutral Beam Injection (NBI) are found unstable. Together with the TAEs, various instabilities associated with the injection of the fast neutrals are observed by multiple diagnostics, and a first characterization is given. Nonlinear wave-wave couplings are also detected through multi-mode analysis, revealing a complex picture of the stability dynamics of the TCV scenario at hand. The measurements provided by a short-pulse reflectometer corroborate the identification and radial localization of the instabilities. A preliminary, but not conclusive, analysis of the impact of TAEs on the amplitude of the electron density fluctuations is carried out. Local flux-tube gyrokinetic simulations show that the dominant underlying instabilities in the absence of fast ions are Trapped Electron Modes (TEM), and that these modes are effectively suppressed by zonal flows. Attempts to simulate the simultaneous presence of fast-ion driven TAEs and TEM turbulence show that elongated streamers develop up to the full radial extent of the flux-tube domain, thereby invalidating the local assumption and indicating that a global approach is mandatory in these TCV plasmas.

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Excitation of toroidal Alfvén eigenmodes with counter-current NBI in the TCV tokamak

Cited by 5 publications

References 25 publications

Predictive modeling of Alfvén eigenmode stability in inductive scenarios in JT-60SA

Predictive modeling of Alfvén eigenmode stability in inductive scenarios in JT-60SA

Determination of MHD mode structures using soft x-ray diagnostics in TCV

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

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