Measurements of 2D poloidal plasma profiles and fluctuations in ECRH plasmas using the heavy ion beam probe system in the TJ-II stellarator

Sharma, R.; Khabanov, P.O.; Melnikov, A. V.; Hidalgo, C.; Cappa, Á.; Chmyga, A. A.; Eliseev, L.G.; Estrada, T.; Kharchev, Ν. K.; Kozachek, A.S.; Krupnik, L. I.; Malaquias, A.; Molinero, A.; Pablos, J.L. de; Pastor, I.; Zenin, V.N.

doi:10.1063/1.5142996

Cited by 11 publications

(10 citation statements)

References 35 publications

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“…Another important factor contributing to the particle transport is the density gradient localization, which is closely connected to the fuelling mechanisms in next step devices. Plasma simulations have investigated the level of inward turbulent particle transport in inverted density gradient regions [4] but validation studies are still at preliminary level [5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…In TJ-II, the first attempt to measure 2D spatial profiles of potential and fluctuations in electron cyclotron resonance heating (ECRH) scenarios was published in [5]. The present paper reports the characterization of 2D poloidal structures of plasma profiles and fluctuations in the enlarged spatial area and extended operational domain of ECRH and neutral beam injection (NBI) scenarios.…”

Section: Introductionmentioning

confidence: 99%

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2D distributions of potential and density mean-values and oscillations in the ECRH and NBI plasmas at the TJ-II stellarator

Melnikov¹,

Eliseev²,

Barcala³

et al. 2022

Plasma Phys. Control. Fusion

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2D plasma potential φ distribution was measured in the electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) plasmas of the TJ-II stellarator with the heavy ion beam probe (HIBP) for the whole radial range and wide area of the poloidal angle, and supported by Langmuir probe data at the edge. The whole operation domain for the on-axis ECRH was explored (n e = 0.45–0.8×1019 m-3, P EC=220–470 kW), ), in addition, NBI plasmas with n e = 0.9–1.3×1019 m-3 and P NBI = 510 kW were studied. In ECRH plasmas the density ramp-up is accompanied by evolution of the potential from the bell-like to Mexican hat profile, while the density profiles were flat or slightly hollow. The potential has the central positive peak, and LFS-HFS (low field - high field sides) and up-down symmetry. Equipotential lines are consistent with vacuum magnetic flux surfaces. In the high-density NBI scenario, the φ profile was fully negative with a minimum up to -300 V at the centre, while at low-density ECRH plasma, φ has a maximum up to +1 kV at the centre. Fluctuations of potential and density are stronger in low-density scenarios and not poloidally symmetric. At the mid-radius (area of the maximum density), RMS of fluctuations were up to φ~15 V at LFS vs ~ 20 V at HFS; RMS ne~2% at LFS vs ~3% at HFS. In the NBI plasmas with the density raise, the asymmetry is decreasing and finally vanishing at n e = 1.2×1019 m-3. 2D distribution of the NBI-induced Alfvén eigenmodes (AEs) shows asymmetric ballooning structure: contrary to broadband turbulence, AE-associated potential perturbation dominates in the LFS with a factor up to 1.7 respect to the HFS. The electrostatic mode, excited in ECRH plasmas by suprathermel electrons also shows an asymmetric structures: density perturbation dominates in the top-bottom direction compared to LFS-HFS direction.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

2D distributions of potential and density mean-values and oscillations in the ECRH and NBI plasmas at the TJ-II stellarator

Melnikov¹,

Eliseev²,

Barcala³

et al. 2022

Plasma Phys. Control. Fusion

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“…The stellarator TJ-II is well suited to investigate the influence of such positive and negative density gradients on plasma fluctuations and transport due to its unique capabilities to control plasma scenarios and magnetic configuration. Results show that plasma density fluctuations appear in both positive and negative density gradient regions in TJ-II plasmas, with normalized levels of density fluctuations that are higher in the negative density gradient region [19].…”

Section: Plasma Fuelling and Impuritiesmentioning

confidence: 93%

Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

Hidalgo¹,

Ascasíbar²,

Alegre³

et al. 2022

Nucl. Fusion

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TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.

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“…Fluid and gyrokinetic simulations have been used to investigate the level of inward turbulent particle transport in the inverted density gradient region [34,35] but comparison of simulations with experimental fluctuation levels and fluxes is still missing. First 2D poloidal contour plots of plasma potential and density fluctuations have been measured with the TJ-II HIBP diagnostic [36], which have allowed to characterise turbulence in positive and negative gradient regions: density fluctuations appear both Damping rate (γ) versus oscillation frequency (Ω) for the experimental oscillations detected in [28]. Data are shown for the specified TJ-II discharges and for numerical simulations, both with a single (grey triangles) and with multiple kinetic species, namely hydrogen ions + electrons + C 4+ impurity ions (circles, squares and pentagrams) [29].The same color is used for experimental points (showing error bars) and for multi-species simulated discharges (without error bars).…”

Section: First Measurements Of Density Fluctuations In Both Positive ...mentioning

confidence: 99%

Overview of recent TJ-II stellarator results

et al. 2019

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The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components. As regards impurity transport research, a number of working lines exploring several recently discovered effects have been developed: the effect of tangential drifts on stellarator neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces and attempts of experimental validation with Doppler reflectometry of the variation of the radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation activities have been performed, the comparison with measurements of zonal flow relaxation in pellet-induced fast transients and the comparison with experimental poloidal variation of fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe array. Another remarkable piece of work has been the investigation of the radial propagation of small temperature perturbations using transfer entropy. Research on the physics and modelling of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced also relevant results. Neutral beam injection driven Alfvénic activity and its possible control by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results on alternative plasma facing components based on liquid metals are also presented.

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Measurements of 2D poloidal plasma profiles and fluctuations in ECRH plasmas using the heavy ion beam probe system in the TJ-II stellarator

Cited by 11 publications

References 35 publications

2D distributions of potential and density mean-values and oscillations in the ECRH and NBI plasmas at the TJ-II stellarator

2D distributions of potential and density mean-values and oscillations in the ECRH and NBI plasmas at the TJ-II stellarator

Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

Overview of recent TJ-II stellarator results

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