Influence of Li conditioning on Lower Hybrid Current Drive efficiency in H-mode and L- mode plasmas on EAST

Goniche, M.; Li, Miaohui; Peysson, Y.; Chen, Yingjie; Ding, Bojiang; Liu, Haiqing; Liu, Yong; Qian, J.; Yang, Xiaodong; Zang, Qing; Zhang, Tao; Zhen, Sun; Zou, X. L.

doi:10.1051/epjconf/201715703018

Cited by 7 publications

(3 citation statements)

References 16 publications

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“…The results indicate that LHCD efficiency is enhanced with strong lithium wall conditioning, according to the comparison between different lithium coating levels. Good wall conditioning can reduce edge recycling, thus can increase the critical density for anomalous loss of CD efficiency [37]. This is consistent with PI modelling results [38] showing that strong lithiation can reduce the PI intensity, due to the higher temperature at the plasma edge with the strong lithiation.…”

Section: Lhcd Efficiency At Higher Densitysupporting

confidence: 85%

Progress of physics understanding for long pulse high-performance plasmas on EAST towards the steady-state operation of ITER and CFETR

Huang¹,

Gong²,

Garofalo³

et al. 2019

Plasma Phys. Control. Fusion

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Recently, the first ever 100 s long, steady-state H-mode discharge with good control of impurities, core and edge MHD stabilities, and heat exhaust was demonstrated in the Experimental Advanced Superconducting Tokamak (EAST) using the ITER-like (International Tokamak Experimental Reactor) tungsten upper divertor. Using both radio frequency (RF) power and neutral beam injection (NBI) heating, EAST has demonstrated fully non-inductive scenarios with an extension of fusion performance at high density and low rotation: β P ∼ 2.5, β N ∼ 2.0, H98,y2 ∼ 1.2, bootstrap current fraction fBS ∼50% at q95 ∼ 6.8. With pure RF power heating, plasmas have been maintained for up to 21 s (over 40 times the current relaxation time) with zero loop voltage and small edge localized modes (ELMs) at high density (ne/nGW ∼ 0.6–0.8), β P ∼ 2.0, β N ∼ 1.6, and ƒBS ∼47%. Experimental investigations show how plasma current profiles, turbulent transport and radiation properties self-consistently evolve toward fusion relevant steady state conditions. Modeling and physics experiments have confirmed the synergistic effects between electron cyclotron heating (ECH) and low hybrid wave (LHW), where ECH enhances the heating and current drive from LHW injection, enabling fully non-inductive operation at higher density. Small/no ELMs facilitate the RF power coupling in the H-mode phase and reduce divertor erosion. A low tungsten concentration was observed at high β P with a hollow profile in the core. Reduction of the peak divertor heat flux with f rad of up to 40% was compatible with the high β P scenario by using active radiation feedback control. With features such as dominant electron heating, zero/low NBI torque and an ITER-like tungsten divertor, fully non-inductive high-performance experiments on EAST offer unique contributions towards the succesful operation of ITER and CFETR (the Chinese Fusion Engineering Testing Reactor).

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Section: Lhcd Efficiency At Higher Densitysupporting

confidence: 85%

Progress of physics understanding for long pulse high-performance plasmas on EAST towards the steady-state operation of ITER and CFETR

Huang¹,

Gong²,

Garofalo³

et al. 2019

Plasma Phys. Control. Fusion

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“…The simulated results are summarized in table 2. It is found that the predicted CD efficiency of the FAM can match with the experiment when an empirical diffusion coefficient of the fast electrons D st = 1 m 2 s −1 is included in the calculation according to [48,49]. The LH current driven by the PAM alone with 1.6 MW power is predicted to be ∼154 kA, corresponding to a CD efficiency ∼0.66 × 10 19 AW −1 m −2 , which is very close to that estimated by the N || -weighted directivity (∼0.61 × 10 19 AW −1 m −2 ).…”

Section: Summary and Discussionmentioning

confidence: 83%

Design and analysis of a PAM launcher at 4.6 GHz for a new LHCD system on EAST

Li,

Liu,

Yang

et al. 2024

Nucl. Fusion

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To improve the current drive (CD) capability in long-pulse (up to ~ 1000 s) H-mode operation, it has been decided to develop a new lower hybrid current drive (LHCD) system at 4.6 GHz with an active cooling passive active multijunction (PAM) launcher on EAST. In this paper, both the RF and the physical properties of this PAM are studied numerically. The same nominal parallel refractive index (N|| = k||c/ω, where k|| is the parallel wavenumber, c the velocity of light, and ω the wave frequency) of 2.04 as the existing 4.6 GHz full active multijunction (FAM) is chosen. Ray-tracing calculations indicate that good accessibility could be achieved when the LH waves radiate with this nominal N|| in typical long-pulse H-mode plasmas. The coupling performance in terms of power reflection coefficient (RC), power spectrum, maximum electric field, power directivity (DP) and global CD capability is evaluated with the ALOHA code based on the linear coupling theory. Good coupling performance with averaged RC ≦ 1% and DP ~ 70% could be expected with the density (ne) in front of the PAM close to the cut-off value (ne_co). The simulated RC remains below 6.5% over a wide density range 0.5 ≦ ne/ne_co ≦ 10, which is similar to the plasma edge conditions produced by edge localized mode (ELM) activity. A detailed comparison with the existing 4.6 GHz FAM launcher is also performed.

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“…It is hypothesized that these four discharges in figure 2 have experienced a high level of parasitic SOL losses, perhaps due to inefficient wall conditioning. Wall conditioning is known to improve current drive efficiency on EAST [42,51,52]. This speculation is supported by a recent LHCD experiment under lithiation [53]: a near non-inductive 500 kA discharge is sustained by 1.5 MW, rather than ∼3 MW, of the 4.6 GHz power at the line-averaged density of 2 × 10 19 m −3 .…”

Section: Ray-tracing/fokker-planck Code: Genray/cql3dmentioning

confidence: 91%

A model investigation of the impact of lower hybrid wave scattering angle on current drive profile in EAST and Alcator C-Mod

Baek¹,

Biswas²,

Wallace³

et al. 2021

Nucl. Fusion

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Lower hybrid current drive (LHCD) is beneficial for developing a steady-state operation scenario in a tokamak. This paper conducts a modeling investigation to identify an optimum rotation angle of the initial lower hybrid perpendicular (to the background magnetic field B) wavevector for best matching the experimental RF current profile. It is hypothesized that central RF power deposition widely observed in the present-day LHCD experiments arises from wave scattering by turbulence. In a standard model without considering such interactions, the predicted power deposition profile is generally broad with off-axis peaking, not in agreement with experimental observations. A heuristic approach is adopted by introducing a spectral broadening mechanism by modifying the initial orientation of the perpendicular wavevector. The ray-tracing/Fokker-Planck solver GENRAY/CQL3D is utilized within the python-based π-scope framework. A focus is given to identify the perpendicular wavenumber orientation angle with respect to the magnetic surface normal vector at the initial ray location. Our modeling study shows that rotating the perpendicular wavevector in such a way as to increase the initial poloidal component is effective in reproducing the centrally peaked current profile observed in normal shear plasmas on both EAST and C-Mod. These waves can readily be absorbed to the central plasma, which reduces the sensitivity of the power deposition profile to a slight change of the plasma condition. The same approach is also found to help broaden the off-axis power deposition profile in a reverse-shear EAST plasma, leading to a better agreement with the experiment. The results presented here suggest that spectral modification arising from edge density fluctuations in a tokamak may need to be considered in understanding wave propagation and absorption. A further experimental and theoretical/modeling study is vital as a reverse approach is adopted in this study. Our work suggests that mitigation or control measures are critical for parasitic effects occurring on the first pass in a reactor regime.

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Influence of Li conditioning on Lower Hybrid Current Drive efficiency in H-mode and L- mode plasmas on EAST

Cited by 7 publications

References 16 publications

Progress of physics understanding for long pulse high-performance plasmas on EAST towards the steady-state operation of ITER and CFETR

Progress of physics understanding for long pulse high-performance plasmas on EAST towards the steady-state operation of ITER and CFETR

Design and analysis of a PAM launcher at 4.6 GHz for a new LHCD system on EAST

A model investigation of the impact of lower hybrid wave scattering angle on current drive profile in EAST and Alcator C-Mod

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