An analysis of controlled detachment by seeding various impurity species in high performance scenarios on DIII-D and EAST

Eldon, D.; Wang, H.Q.; Wang, L.; Barr, J.L.; Ding, Siye; Garofalo, A. M.; Gong, Xianzu; Guo, H.Y.; Järvinen, A.; Li, K.D.; McClenaghan, Joseph; McLean, A.G.; Samuell, Cameron; Watkins, J. G.; Weisberg, David B.; Yuan, Q.P.

doi:10.1016/j.nme.2021.100963

Cited by 21 publications

(22 citation statements)

References 48 publications

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“…To protect the divertor target during long-pulse operation in EAST, the detachment feedback control modules of j s , T et , and so on have been developed successfully with impurity seeding [13,26,[39][40][41]. In shots #87657 and #93411, via a feedback control scheme, T et around the upper outer strike point (T et,UOSP ) both decreased from ∼40 eV to ∼5 eV with Ar or Ne seeding, as shown in figures 2 and 3.…”

Section: Detachment Behavior On the Upper Outer Divertormentioning

confidence: 99%

Comparison of divertor behavior and plasma confinement between argon and neon seeding in EAST

Yang

Wang

et al. 2021

Nucl. Fusion

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The exhaust of excessively high heat and particle fluxes on the divertor target is crucial for EAST long-pulse operation. In the recent EAST experiments, stable partial energy detachment around the upper outer strike point with H 98,y2 ∼ 1 was achieved with either Ne or Ar seeding from the upper outer divetor target in the upper single null configuration with ITER-like tungsten divertor. With either Ar or Ne seeding, the electron temperature around the upper outer strike point (T et,UOSP) was maintained at around 5 eV, the peak temperature of divertor target surface around the upper outer strike point (T div,UO) decreased significantly, and material sputtering was well suppressed. It was observed that there was less Ar seeding needed for partial energy detachment onset than Ne seeding, which shows that Ar is more efficient in the cooling of T et on the upper outer divertor than Ne. However, there was no detachment on the upper inner divertor with T et around strike point (T et,UISP) remaining >10 eV with either Ar or Ne seeding from the upper outer divertor. Accompanied with the disappearance of double peak phenomenon of ion flux density on the upper inner divertor target (j s,UI), the peak T div,UI around the strike point increased to around 300 °C. Although the heat flux on the upper inner divertor target (q t,UI) is still in the acceptable level, either Ar or Ne seeding only from the upper outer divertor target is not enough to protect the upper inner divertor target from sputtering under current EAST conditions. On the other hand, Ar seeding always causes confinement degradation in the partial energy detachment state. It was observed that there is a slight confinement improvement (∼10%) with Ne seeding, which may be due to density peaking, dilution effects and stabilization of the ion temperature gradient mode.

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Section: Detachment Behavior On the Upper Outer Divertormentioning

confidence: 99%

Comparison of divertor behavior and plasma confinement between argon and neon seeding in EAST

Yang

Wang

et al. 2021

Nucl. Fusion

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“…Therefore, the development of new detachment feedback controllers in high β P scenario is needed. In the DIII-D 2018 campaign, the feedback control of radiation was utilized and demonstrated in the high β P scenario [10,16], which accessed partial divertor detachment successfully in LSN configuration. In 2019, a more precise controller utilizing the divertor Langmuir probe measured particle flux (J sat ) to characterize the degree of detachment (DoD) was successfully developed and demonstrated in the high β P scenario, similar to the jointly developed J sat controller in the EAST tokamak [14] and JET [8].…”

Section: Detachment Feedback Controller Development In Diii-d High β ...mentioning

confidence: 99%

“…In EAST, actively feedback controlled H-mode detachment with simultaneous T et,div ∼ 5 eV and energy confinement enhanced factor H 98 > 1 was achieved using either divertor neon or argon seeding with the ITER-like tungsten divertor. In addition, different new detachment feedback controllers including divertor Langmuir probe measured T et,div [16,17], T et,div guided P rad,X-point [18], infra-red thermography measured target surface temperature [19] have all been developed and utilized successfully in EAST. In DIII-D, full detachment with T et,div 5 eV and very low particle flux across the entire target was achieved with H 98 ∼ 1.5, β N ∼3, β P > 2 and β T ∼ 2-2.5% by utilizing feedback controlled impurity seeding in the high β P scenario [20,21] I p is the normalized beta, where B is the total magnetic field, B T is the toroidal magnetic field, B p is the poloidal magnetic field, I p is the plasma current, a is the plasma minor radius, p is the plasma pressure.…”

Section: Introductionmentioning

confidence: 99%

Achievements of actively controlled divertor detachment compatible with sustained high confinement core in DIII-D and EAST

Wang

Eldon

et al. 2022

Nucl. Fusion

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The compatibility of efficient divertor detachment with high-performance core plasma is vital to the development of magnetically controlled fusion energy. The joint research on the EAST and DIII-D tokamaks demonstrates successful integration of divertor detachment with excellent core plasma confinement quality, a milestone towards solving the critical Plasma-wall-interaction (PWI) issue and core-edge integration for ITER and future reactors. In EAST, actively controlled partial detachment with Tet,div ~ 5 eV around the strike point and H98 > 1 in different H-mode scenarios including the high βP H-mode scenario have been achieved with ITER-like tungsten divertor, by optimizing the detachment access condition and performing detailed experiments for core-edge integration. For active long pulse detachment feedback control, a 30s H-mode operation with detachment-control duration being 25s has been successfully achieved in EAST. DIII-D has achieved actively controlled fully detached divertor with low plasma electron temperature (Tet,div ≤ 5 eV across the entire divertor target) and low particle flux (degree of detachment, DoD >3), simultaneously with very high core performance (βN ~3, βP >2 and H98~1.5) in the high βP scenario being developed for ITER and future reactors. The high-βP high confinement scenario is characterized by an internal transport barrier (ITB) at large radius and a weak edge transport barrier (ETB, or pedestal), which are synergistically self-organized. Both the high-βP scenario and impurity seeding facilitate divertor detachment. The detachment access leads to the reduction of ETB, which facilitates the development of an even stronger ITB at large radius in the high βP scenario. Thus, this strong large radius ITB enables the core confinement improvement during detachment. These significant joint DIII-D and EAST advances on the compatibility of high confinement core and detached divertor show a great potential for achieving a high-performance core plasma suitable for long pulse operation of fusion reactors with controllable steady-state PWIs.

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“…In addition, target T e and ion saturation current (J sat ) from floor probes, and the observed 30% reduction of the measured outer divertor strike point (OSP) heat flux, confirmed the OSP was at the onset of detachment during the time the high pedestal pressure was maintained [58]. Advanced control algorithms [61,62] were used to achieve these results including the use of feedback-controlled 3D fields for density control and feedback nitrogen gas puffing for divertor radiated power control. All of these results suggest that it may be desirable to look into SH-like pedestal pressure enhancements in ITER scenarios with detached radiative divertors.…”

Section: Scenarios Integrating High Performance Core and Boundarymentioning

confidence: 85%

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

et al. 2022

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DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

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An analysis of controlled detachment by seeding various impurity species in high performance scenarios on DIII-D and EAST

Cited by 21 publications

References 48 publications

Comparison of divertor behavior and plasma confinement between argon and neon seeding in EAST

Comparison of divertor behavior and plasma confinement between argon and neon seeding in EAST

Achievements of actively controlled divertor detachment compatible with sustained high confinement core in DIII-D and EAST

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

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