On confinement characteristics of the newly developed sawtooth-free plasmas in KSTAR tokamak

Byun, Cheol-Sik; Na, Yong-Su; Kim, Hyeong‐Seog; Kim, S.-H.

doi:10.1016/j.cap.2013.10.014

Cited by 5 publications

(6 citation statements)

References 13 publications

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“…As shown, the 1st NB was injected during the current ramp-up phase and the 2nd and the 3rd NB were injected at the same time right after the current overshoot. The waveform of the plasma current such as the maximum plasma current value, plasma current ramp-down rate and main heating timing was designed to optimise the s/q profile based on a variety of ASTRA predictive simulations [32]. As shown in figure 5, the plasma performance began to increase during the plasma current overshoot at around 1.8 s. The performance was further increased after the main heating was applied, but degraded due to the n = 1 and or n = 2 mode.…”

Section: Plasma Current Overshoot Approachmentioning

confidence: 99%

On hybrid scenarios in KSTAR

Na¹,

Lee²,

Byun³

et al. 2020

Nucl. Fusion

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We report the status of hybrid scenario experiments in Korea Superconducting Tokamak Advanced Research (KSTAR). The hybrid scenario is defined as stationary discharges with β N ⩾ 2.4 and H 89 ⩾ 2.0 at q 95 < 6.5 without or with very mild sawtooth activities in KSTAR. It is being developed towards reactor-relevant conditions. High performance of β N ≲ 3.0, H 89 ≲ 2.4 and G-factor (≡ β N H 89 /q 2 95 ) ≲ 0.46 has been achieved and sustained for ≳ 40τ E at n e /n GW ~0.7 with heating power of ≲5 MW. Some KSTAR hybrid discharges exhibit a unique feature of a slow transition from conventional H-mode to hybrid mode after the third neutral beam injection. The reason for the confinement enhancement is extensively studied in this transition period of a representative discharge exhibiting a common feature of KSTAR hybrid scenarios. 0D performance analysis with magnetohydrodynamic activities, 1D kinetic profile dynamics, power balance analysis, linear gyro-kinetic analysis and edge pedestal stability analysis were conducted. The enhancement is thought to be from both the core and the pedestal. The improvement in the core region of the ion energy channel is observed from the linear gyro-kinetic analysis considering the electromagnetic, the fast ion, the Shafranov shift, ω E×B , and the magnetic shear effect. The electromagnetic finite β stabilisation plays a role in the inner core region at ρ tor ∼ 0.35 together with the fast ion effect. The alpha stabilisation effect is also found at ρ tor ∼ 0.5. ω E×B , which could reduce the linear growth of the ion temperature gradient mode in the outer core region at ρ tor ∼ 0.5 − 0.7 with the highest contribution from the toroidal rotation. Regarding the improvement in the pedestal, Shafranov shift broadens the stability boundary of the pedestal in support of the diamagnetic effect. The pedestal height and width could be reproduced by the EPED model, while a realistic current profile is used to calculate the internal inductance for Shafranov shift. Based on these findings, a comprehensive confinement enhancement mechanism has been proposed by considering the core-edge interplay.

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Section: Plasma Current Overshoot Approachmentioning

confidence: 99%

On hybrid scenarios in KSTAR

Na¹,

Lee²,

Byun³

et al. 2020

Nucl. Fusion

Self Cite

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“…To generate the Alfvénic activity easily with the sub-Alfvénic beamions, high q min (or high q 0 ) scenario was selected because the elevated central safety factor (q) profile with weak magnetic shear has less continuum damping. This scenario with q 0 over 1.5 (higher than 2.0 in the initial stage of discharge) has been achieved by the early shaping (diverting) recipe [31,72] and the off-axis ECCD so as to delay the plasma current diffusion.…”

Section: Experiments For the Tae Control Feasibility Using The Eccdmentioning

confidence: 99%

“…Maximum beam power and energy are about 5.0 MW and 100 keV, respectively. Since the nominal beam energy (60-100 keV) is sub-Alfvénic under the condition of the usual toroidal field strength (1.5-3.0 T) on KSTAR, destabilization of AEs occurs via the sideband resonances (v b ∼ v A /3) with the shear Alfvén waves [31,34]. v b and v A are the parallel speed of the beam ion and the Alfvén speed, respectively.…”

Section: Heating Current Drive and Diagnosticsmentioning

confidence: 99%

Suppression of toroidal Alfvén eigenmodes by the electron cyclotron current drive in KSTAR plasmas

et al. 2022

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Advanced operation scenarios such as high poloidal beta (βP) or high q min are promising concepts to achieve the steady-state high-performance fusion plasmas. However, those scenarios are prone to substantial Alfvénic activity, causing fast-ion transport and losses. Recent experiments with the advanced operation scenario on KSTAR tokamak have shown that the electron cyclotron current drive (ECCD) is able to mitigate and suppress the beam-ion driven toroidal Alfvén eigenmodes (TAEs) for over several tens of global energy confinement time. Co-current directional intermediate off-axis ECCD lowers the central safety factor slightly and tilts the central q-profile shape so that the continuum damping in the core region increases. Besides, the rise of central plasma pressure and increased thermal-ion Landau damping contribute to TAE stabilization. While the TAEs are suppressed, neutron emission rate and total stored energy increase by approximately 45% and 25%, respectively. Fast-ion transport estimated by TRANSP calculations approaches the classical level during the TAE suppression period. Substantial reduction in fast-ion loss and neutron deficit is also observed. Enhancement of fast-ion confinement by suppressing the TAEs leads to an increase of non-inductive current fraction and will benefit the sustainment of the long-pulse high-performance discharges.

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“…Korea Superconducting Tokamak Advanced Research (KSTAR) [13,14] is addressing the establishment of highperformance, steady-state operations with various advanced operation scenarios [15][16][17][18][19][20][21][22]. Among them, hybrid scenarios have been explored for years [23,24]. Hybrid scenarios have been attempted by utilizing three co-direction on-axis Neutral Beam Injection (NBI) sources providing up to 5 MW as the primary heating source [25].…”

Section: Introductionmentioning

confidence: 99%

Effect of coherent edge-localized mode on transition to high-performance hybrid scenarios in KSTAR

Lee,

Kim,

Kim

et al. 2023

Nucl. Fusion

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This paper deals with one of the origins and trigger mechanisms responsible for the observed performance enhancements in the hybrid scenario experiments conducted in Korea Superconducting Tokamak Advanced Research (KSTAR). The major contribution to the performance improvement comes from the broader and higher pedestal formation. The increase of fast ion pressure due to the plasma density decrease also contributes substantially to the global beta. Although the reduced core plasma volume resulting from the pedestal expansion has a negative effect on the core thermal energy, a considerable confinement improvement observed in the inner core region limits the degradation. The one significant characteristic of high-performance discharges is the presence of coherent edge-localized mode (CEM) activity. CEM is triggered during the pedestal recovery phase between typical ELM crashes and has been found to be related to the increase of particle and heat transport. It appears to underlie two commonly observed phenomena in high-performance hybrid scenario discharges in KSTAR: pedestal broadening and continuous density decrease. Despite the associated transport increase, CEM activities can induce performance enhancement. With the pedestal broadening, ELM crashes become delayed and weakened, which, in turn, allows for a higher pedestal. Moreover, the density decrease directly increases fast ion pressure by extending the beam-slowing-down time. The linear gyrokinetic analysis reveals that the increase of fast ions could initiate positive feedback loops, leading to the stabilization of ion temperature gradient mode (ITG) in the inner core region.

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On confinement characteristics of the newly developed sawtooth-free plasmas in KSTAR tokamak

Cited by 5 publications

References 13 publications

On hybrid scenarios in KSTAR

On hybrid scenarios in KSTAR

Suppression of toroidal Alfvén eigenmodes by the electron cyclotron current drive in KSTAR plasmas

Effect of coherent edge-localized mode on transition to high-performance hybrid scenarios in KSTAR

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