Lower hybrid wave absorption study to improve the calculation of energy confinement time in EAST

Gu, Xiaojing; Shen, Biao; Li, Miaohui; Qian, Jinping; Moreau, D.; Ding, Siye; Sun, Yuan; Ding, Baoqing; Chen, Shaohua

doi:10.1063/1.5047226

“…Here, P heat is the sum of Ohmic and auxiliary heating powers after subtracting the unabsorbed parts of the injected powers, and W is the plasma stored energy which is calculated in the usual way from the magnetic equilibrium (W MHD ). The calculation of the absorbed auxiliary heating power for different heating methods (LHW, ECCD, NBI) in EAST can be seen in references [16,21,22]. The scaling of the L-H transition power threshold P scale is evaluated according to the latest version of threshold scaling for deuterium plasmas [23] as,…”

Section: Reduced P L-h By LI Wall Conditioningmentioning

confidence: 99%

On the role of the hydrogen concentration in the L-H transition power threshold in EAST

Shao

¹

,

Xu

²

,

Yu

³

et al. 2020

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A decrease in the L-H transition power threshold P L-H under the lithium wall conditioning has been observed since 2010 in EAST. The physical mechanism responsible for the reduced P L-H is found to be related to three phases of wall recycling as determined by the accumulation of lithium in the vessel. In phase I (a few rounds of wall conditioning) the wall recycling is low, while no clear variation of L-H transition power threshold is observed. In phase II (after another few rounds of wall conditioning) a clear increase in the wall recycling is observed, leading to decreased L-H transition power threshold. In phase III the wall recycling is higher and the hydrogen concentration n H / ( n H + n D ) is lower compared to phases I and II. In this third phase the L-H transition power threshold is mainly reduced by the decreased n H / ( n H + n D ) . During phase III of the wall recycling, the quantitative relationship between the hydrogen content and normalized L-H transition power threshold P L-H / P s c a l e is studied for campaigns in 2010, 2012, 2015 and 2016. Data scaling reveals that P L − H / P s c a l e = ( − 1.513 ± 0.135 ) × e ( − 6.989 ± 0.362 ) × n H / ( n H + n D ) + ( 1.698 ± 0.050 ) in the hydrogen concentration range of 3–45%, i.e. P L-H / P s c a l e increases significantly for 3 % < n H / ( n H + n D ) < 20 % , while it increases mildly for 20 % < n H / ( n H + n D ) < 45 % .

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“…The absorption efficiency and current drive efficiency of 2.45 GHz waves become much worse than that of 4.6 GHz waves at high density (roughly n e > 2.4 × 10 19 cm −3 ) [67,68], and therefore the applied power of 2.45 GHz waves in practice for the β p scenario is very small. Replacing LH waves at 2.45 GHz by additional LH waves at 4.6 GHz has been proposed as an upgrade option in the years to come to improve effective RF heating and current drive for steady-state high-performance plasmas on EAST.…”

Section: Predictive Modeling Of East Steady-state High-performance Pl...mentioning

confidence: 99%

Validation of theory-based integrated modeling and new insights for a high-performance steady-state scenario with only RF heating on EAST

Zhai¹,

Chen²,

Xiang³

et al. 2022

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Theory-based integrated modeling is validated against high-performance steady-state core plasmas on EAST in high poloidal beta (β_p) regime with only RF heating. Reasonably good agreement between the modeling results and experimental measurements is obtained not only for the temperature profiles but also for the 11-chord line-integrated densities and Faraday angles for the first time. This validation effort demonstrates that the safety factor profiles can be non-reversed in high β_p experiments on EAST. The inaccessibility for LH waves observed in conventional ray-tracing simulations for some high β_p experiments is effectively mitigated by including the modeling of wave propagation in scrape-off layer. The observed confinement improvement with density increasing (Gong X, Garofalo A M, Huang J, et al. Nuclear Fusion 2019 59 086030) can be attributed to the reduction of turbulent transport by the collisional stabilization on trapped electron modes rather than by the Shafranov shift stabilization effect which was proposed to be the major cause of confinement enhancement in previous literatures. Based on the successful validation and newly gained physical insights, predictive modeling is performed for core plasma with the upgraded capacity of LH wave system in the upcoming few years and it is shown that the high-performance steady-state H-mode scenario on EAST can be extended to the regime with q95 to be ITER relevant.

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“…Compared with the previous H-mode with LH alone reported in [31], these H-mode discharges show higher confinement. This is because the LH heating effects will become poor at high density, as observed in [40]. With the increase in available ECRH power, the dependence of global confinement on the plasma current, heating power, and plasma density will be investigated in depth in the future.…”

Section: H-mode Characterizationmentioning

confidence: 99%

Plasma heating by electron cyclotron wave and the temperature effects on lower hybrid current drive on EAST

Li

¹

,

Xu²,

Wang³

et al. 2023

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This paper presents the progress in the long - pulse operation of the electron cyclotron (EC) system and the achievements in high - electron temperature plasmas by the combined EC and lower hybrid (LH) waves heating since the EC system was built in 2015. An electron temperature of up to 12 keV with a duration over 100 s was realized by the simultaneous heating of EC and LH waves at the line-averaged density n ̅_e ~ 1.8 *10^19/m^3. The plasma heating effect strongly depends on the location of EC power deposition. H-mode plasmas with solely EC wave auxiliary heating have been obtained on EAST for the first time. These H-mode discharges show an enhanced confinement factor H98(y,2) around 1.0, which is higher than the previous H-mode using LH power alone [G.S. Xu et al Nucl. Fusion 51 (2011) 072001]. The total heating power is very close to the threshold value for L-H transition according to the international tokamak scaling. In addition to the temperature effects inside the separatrix, higher electron temperature produced by EC wave is found to reduce the LH power loss in the scrape-off layer (SOL) due to collisional absorption, which is beneficial to further increase the lower hybrid current drive (LHCD) efficiency. Ray-tracing/Fokker-Planck modeling results indicate that higher electron temperature can shorten the LH wave propagation on EAST in a multiple-pass regime, thus decreasing the collisional dissipation.

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Lower hybrid wave absorption study to improve the calculation of energy confinement time in EAST

Cited by 17 publications

References 24 publications

On the role of the hydrogen concentration in the L-H transition power threshold in EAST

On the role of the hydrogen concentration in the L-H transition power threshold in EAST

Validation of theory-based integrated modeling and new insights for a high-performance steady-state scenario with only RF heating on EAST

Plasma heating by electron cyclotron wave and the temperature effects on lower hybrid current drive on EAST

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