Behavior of Detachment Front in a Tokamak Divertor

Nakazawa, S.; Nakajima, N.; Okamoto, Masayuki; Ohyabu, N.

doi:10.1002/1521-3986(200006)40:3/4<491::aid-ctpp491>3.0.co;2-m

Cited by 3 publications

(5 citation statements)

References 3 publications

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“…Electron heat conduction is not always a complete description of parallel heat flow. There is evidence in prior and existing experiments that sometimes substantial heat flux passes through into the cold side of the radiation front [31,34,36,60]. Because electron thermal conduction is small at low temperature, convective heat transport by net particle flow along the field is suggested as the reason for the measured heat fluxes [60].…”

Section: Emission Localization Neutrals and Multidimensional Effectsmentioning

confidence: 94%

“…The detailed physics of divertors and detachment includes both complicated atomic physics and multi-dimensional transport effects. The effect of atomic physics on detachment has been considered in 2D models with full divertor geometry [31,32], simplified 2D slab models [33] and 1D models [34][35][36][37]. In all these models, charge exchange collisions and recombination are important to explain the pressure drop between the X-point and the divertor plates.…”

Section: Introductionmentioning

confidence: 99%

“…Even when impurity radiation dominates and is localized in a thin thermal front, theoretical arguments and numerical evidence suggest that 2D geometrical effects can be important to reproduce observations [38,39]. In 1D models, charge exchange collisions appear to be an energy dissipation mechanism comparable to radiation [34,36], although these models tend to overpredict the effect of charge exchange losses by assuming that all charge exchanged ions carry their entire energy and momentum directly to surrounding surfaces.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of detachment extent to magnetic configuration and external parameters

2016

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Divertor detachment may be essential to reduce heat loads to magnetic fusion tokamak reactor divertor surfaces. Yet in experiments it is difficult to control the extent of the detached, low pressure, plasma region. At maximum extent the front edge of the detached region reaches the X-point and can lead to degradation of core plasma properties. We define the ‘detachment window’ in a given position control variable C (for example, the upstream plasma density) as the range in C within which the front location can be stably held at any position from the target to the X-point; increased detachment window corresponds to better control. We extend a 1D analytic model [] to determine the detachment window for the following control variables: the upstream plasma density, the impurity concentration and the power entering the scrape-off layer (SOL). We find that variations in magnetic configuration can have strong effects; increasing the ratio of the total magnetic field at the X-point to that at the target, , (total flux expansion, as in the super-x divertor configuration) strongly increases the detachment window for all control variables studied, thus strongly improving detachment front control and the capability of the divertor plasma to passively accommodate transients while still staying detached. Increasing flux tube length and thus volume in the divertor, through poloidal flux expansion (as in the snowflake or x-divertor configurations) or length of the divertor, also increases the detachment window, but less than the total flux expansion does. The sensitivity of the detachment front location, zh, to each control variable, C, defined as , depends on the magnetic configuration. The size of the radiating volume and the total divertor radiation increase and , respectively, but not by increasing divertor poloidal flux expansion or field line length. We believe this model is applicable more generally to any thermal fronts in flux tubes with varying magnetic field, and similar sources and sinks, such as detachment fronts in stellarator divertors and solar prominences in coronal loops.

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Section: Emission Localization Neutrals and Multidimensional Effectsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sensitivity of detachment extent to magnetic configuration and external parameters

2016

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“…In the context of developing reduced fluid model for neutrals [20,24] we propose in this work a simple diffusive model to evaluate the neutral density n n . Despite its overall simplicity, this reduced model is appropriate for understanding the effect of the ionization source on the plasma flows on the divertor target [25]. It allows to get a rather realistic description of the plasma in front of the target and, thanks to the recycling process at the wall, it provides a self-consistent source of particle which is required to get a more reliable particles balance in the simulations.…”

Section: A Diffusive Model For Neutralsmentioning

confidence: 99%

Core-edge 2D fluid modeling of full tokamak discharge with varying magnetic equilibrium: from WEST start-up to ramp-down

et al. 2022

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In the present work we investigate for the ﬁrst time the 2D ﬂuid transport of the plasma in WEST during an entire discharge from the start-up to the ramp-down (shot #54487). The evolution of density proﬁle, electron and ion temperatures together with the experimental magnetic equilibrium, total current and gas-puﬀ rate is investigated. Comparisons with the interferometry diagnostic show a remarkable overall qualitative agreement during the discharge that can be quantitative at some locations in the plasma core. If at the onset of the X-points during the ramp-up the electron heat ﬂux is dominant at the target, present results show that the ion heat ﬂux becomes dominant during the stationary phase of the discharge. Using a simple model for erosion, present results assess the tungsten sputtering due to deuterium ions during the start-up and ramp-up phases of the discharge and conﬁrms the need to consider full discharge simulation to accurately treat the W source of contamination. This work also demonstrates the interest of developing magnetic equilibrium free solver including eﬃcient time integration to step toward predictive capabilities in the future for fusion operation.

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“…4͑b͒. 18,29,30 The size of the recycling zone can be represented by the distance between the plasma density peak and the divertor plate, and it amounts to a few centimeters for the illustrated cases in Fig. 4.…”

Section: -5mentioning

confidence: 99%

Fluid-particle hybrid simulation on the transports of plasma, recycling neutrals, and carbon impurities in the Korea Superconducting Tokamak Advanced Research divertor region

Kim

Hong

2005

Physics of Plasmas

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A two-dimensional simulation modeling that has been performed in a self-consistent way for analysis on the fully coupled transports of plasma, recycling neutrals, and intrinsic carbon impurities in the divertor domain of tokamaks is presented. The numerical model coupling the three major species transports in the tokamak edge is based on a fluid-particle hybrid approach where the plasma is described as a single magnetohydrodynamic fluid while the neutrals and impurities are treated as kinetic particles using the Monte Carlo technique. This simulation code is applied to the KSTAR ͑Korea Superconducting Tokamak Advanced Research͒ tokamak ͓G. S. Lee, J. Kim, S. M. Hwang et al., Nucl. Fusion 40, 575 ͑2000͔͒ to calculate the peak heat flux on the divertor plate and to explore the divertor plasma behavior depending on the upstream conditions in its base line operation mode for various values of input heating power and separatrix plasma density. The numerical modeling for the KSTAR tokamak shows that its full-powered operation is subject to the peak heat loads on the divertor plate exceeding an engineering limit, and reveals that the recycling zone is formed in front of the divertor by increasing plasma density and by reducing power flow into the scrape-off layer. Compared with other researchers' work, the present hybrid simulation more rigorously reproduces severe electron pressure losses along field lines by the presence of recycling zone accounting for the transitions between the sheath limited and the detached divertor regimes. The substantial profile changes in carbon impurity population and ionic composition also represent the key features of this divertor regime transition.

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Behavior of Detachment Front in a Tokamak Divertor

Cited by 3 publications

References 3 publications

Sensitivity of detachment extent to magnetic configuration and external parameters

Sensitivity of detachment extent to magnetic configuration and external parameters

Core-edge 2D fluid modeling of full tokamak discharge with varying magnetic equilibrium: from WEST start-up to ramp-down

Fluid-particle hybrid simulation on the transports of plasma, recycling neutrals, and carbon impurities in the Korea Superconducting Tokamak Advanced Research divertor region

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