Compatibility of detached divertor operation with robust edge pedestal performance

Leonard, A.W.; Makowski, M. A.; McLean, A.G.; Osborne, T.H.; Snyder, P. B.

doi:10.1016/j.jnucmat.2014.11.007

Cited by 20 publications

(19 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Strong gas puffing tends to degrade the pedestal performance in the DIII-D tokamak [13,14] as also reported on other tokamaks [6,7]. As shown in figure 2, with both closed and open divertors and for both 5 MW and 3 MW cases, increasing the pedestal density by increasing gas-puffing rate reduces both the pedestal temperature and pressure, especially when approaching detachment.…”

Section: Pedestal Heightsupporting

confidence: 70%

“…However, such a displacement is greatly enhanced in the detached plasma when operating in closed divertor but reduced when operating in open divertor. As shown in figure 7, high gas puffing moves the density pedestal radially outward or closer to the separatrix, and cools the plasma near the separatrix, which has also been confirmed in many machines [6,7,13]. The temperature pedestal also moves towards the separatrix in the open divertor and the displacement remains small.…”

Section: Pedestal Displacementsupporting

confidence: 57%

“…But it is still not clear how the boundary plasma conditions quantitatively affect the pedestal structure and thus the plasma confinement. In particular, when the plasma approaches divertor detachment, which is essential for the high heat flux operation of future reactor-relevant devices [12][13][14], more neutrals are ionized near/inside the pedestal, which may greatly affect the pedestal fueling and height. In addition, some experimental results have shown that, although the pedestal width is highly consistent with the EPED model based on the kinetic-ballooning-mode constraint [15][16][17], the position of density pedestal top relative to the separatrix (determined from the temperature profiles, see section 2) is consistent with the neutral penetration model, suggesting the important role of neutrals on the pedestal width…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effects of divertor geometry on H-mode pedestal structure in attached and detached plasmas in the DIII-D tokamak

et al. 2018

Self Cite

View full text Add to dashboard Cite

Dedicated experiments have been performed in the DIII-D tokamak to assess the influence of divertor geometry on the H-mode pedestal structure. It has been found that in both attached and detached plasmas, compared to the open divertor, the more closed divertor results in lower density at the pedestal top. Higher pedestal performance can be achieved with the closed divertor in detached plasmas, as manifested by a higher pedestal temperature at the same pedestal density, by about a factor of two, than the open divertor. In addition, approaching divertor detachment by increasing the gas-puffing rate, for different divertor geometries, the pedestal width exhibits different trends. In the attached plasma, the pedestal width agrees well with the theoretical and empirical pedestal-poloidal-beta scaling. However, during divertor detachment, in the open divertor the pedestal width is significantly reduced. In contrast, for detached plasmas with the more closed divertor, the pedestal is significantly wider, by up to 50%, compared to the theoretical scaling. Moreover, near divertor detachment, the open diverted plasma exhibits a more aligned density and temperature pedestal profile, while in the closed divertor the detachment results in a relative shift (up to 50% of the pedestal width) between the density and temperature pedestal profiles.

show abstract

Section: Pedestal Heightsupporting

confidence: 70%

Section: Pedestal Displacementsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of divertor geometry on H-mode pedestal structure in attached and detached plasmas in the DIII-D tokamak

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…The blue and red curves correspond closely to the pre-puff and gas puffing cases discussed in figures 3 and 4; the green curves correspond to a time slice a few hundred milli-seconds following ECH cut-off in the high power case. Although the pedestal density and the density gradient in both power cases increased with gas puffing, the density width in the pedestal w n decreased as density increased in the moderate power case (figure 5(a)), as is typical in lower power DIII-D discharges [14], but was essentially unchanged in the high power case, as shown in figure 5(b). One notes that there was little density fall-off between the primary and secondary separatrices, and in fact the density appears to increase toward the secondary separatrix.…”

Section: Comparison Of High Performance Plasmas At Moderate and High ...mentioning

confidence: 73%

Improved confinement in highly powered high performance scenarios on DIII-D

et al. 2017

View full text Add to dashboard Cite

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95 = 6, P IN up to 15 MW, H 98 = 1.4-1.8, and β N = 2.5-4.0. The ion B × ∇B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g. ⩽11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g. ⩾14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both τ E and β N in the high power cases (⩾14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peelingballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher τ E and β N than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. We find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.

show abstract

“…Scientists developed particle (either fueling or impurity) injection technique to achieve a so-called 'detachment' state, which enables low temperature (below a few eV) and low particle flux on divertor plates (Stangeby 2000). In most present experiments, it is commonly found that divertor detachment significantly reduces the plasma performance, as the detachment front cools the core plasma through a degrading of the H-mode pedestal (Asakura et al 2009;Kallenbach et al 2015;Leonard et al 2015). An experimental approach for a promising edge solution and with high-core performance compatibility is highly desired.…”

Section: Edge Solution: Detached Divertor and Small/no Elmsmentioning

confidence: 99%

Progress in the development and understanding of a high poloidal-beta tokamak operating scenario for an attractive fusion pilot plant

Ding

Garofalo

2022

Rev. Mod. Plasma Phys.

View full text Add to dashboard Cite

The high poloidal-beta ($$\beta _{\textrm{P}}$$ β P ) regime was first proposed as a high bootstrap current scenario for a steady-state fusion pilot plant (FPP) in the 1990s (Kikuchi in Nucl Fusion 30:265, 1990). Since then, there have been many theoretical, modeling, and experimental research activities on this topic. A joint DIII-D/EAST research team began exploring the high-$$\beta _{\textrm{P}}$$ β P regime in 2013, focusing on addressing the needs of attractive FPP design by taking advantage of the extensive diagnostic set and sophisticated plasma control system on DIII-D and the well-developed integrated modeling capability at General Atomics. The ultimate goal is to demonstrate such a scenario on EAST with truly long pulse and metal wall compatibility. This paper summarizes the highlights of the research results on DIII-D by the joint team in the past decade. Experimental evidence and modeling analysis show the high-$$\beta _{\textrm{P}}$$ β P scenario has great advantages in addressing key needs for an attractive FPP design, such as high-energy confinement quality at low rotation, excellent core-edge integration, high line-averaged density above the Greenwald limit, low disruption risk, and high bootstrap current fraction for steady-state operation. This provides a relatively safe and economical option to base an FPP design on that will lead to commercial fusion energy.

show abstract

Compatibility of detached divertor operation with robust edge pedestal performance

Cited by 20 publications

References 19 publications

Effects of divertor geometry on H-mode pedestal structure in attached and detached plasmas in the DIII-D tokamak

Effects of divertor geometry on H-mode pedestal structure in attached and detached plasmas in the DIII-D tokamak

Improved confinement in highly powered high performance scenarios on DIII-D

Progress in the development and understanding of a high poloidal-beta tokamak operating scenario for an attractive fusion pilot plant

Contact Info

Product

Resources

About