Parametric analyses of divertor plasmas

Parbhakar, K.; Post, D.

doi:10.1016/0022-3115(87)90461-2

Cited by 6 publications

(6 citation statements)

References 4 publications

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“…In fluid models of SOL transport it is commonly assumed that the ion flow is sonic at the entrance to the collector sheath region (i.e. the Bohm sheath criterion is satisfied), even when ionization and NUCLEAR FUSION, Vol.30, No.M (1990) collision events occur in the vicinity of the plate [22,[24][25][26]. This assumption appears to be valid on the basis of the results presented by Andrews and Stangeby [27].…”

Section: Ion Flow Energymentioning

confidence: 62%

“…6 of Ref. [25]), and then increases rapidly to its maximum value at the sheath boundary. A similar behaviour was observed in the v' = 0 .…”

Section: Ion Flow Energymentioning

confidence: 84%

“…5 of Ref. [25]). The flow velocity increases from zero at the midplane, exhibits a moderate dip near the location of the peak ionization rate (as shown in Fig.…”

Section: Ion Flow Energymentioning

confidence: 88%

“…This difference may be the reason for the diametrically opposite conclusions regarding the applicability of the Bohm criterion for such a system. Parbhakar and Post [25] have studied the dependence of neutral particle recycling from the divertor plate on the ion flow velocity at the plasma-sheath interface. Their one-dimensional SOL model couples a single-fluid description of plasma transport with a neutral particle transport package.…”

Section: Ion Flow Energymentioning

confidence: 99%

“…Their one-dimensional SOL model couples a single-fluid description of plasma transport with a neutral particle transport package. They report that high recycling equilibria are only possible when 3TI < 0.7, where 3H is the Mach number at the sheath boundary [25]. For low values of 3H, the system always produced a large amount of recycled neutral gas.…”

Section: Ion Flow Energymentioning

confidence: 99%

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Particle simulations of collisional transport in a high recycling, diverted tokamak scrape-off layer

1990

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The transport of particles and energy through a high recycling divertor scrape-off layer (SOL) in a tokamak is studied via a kinetic transport model. This model combines particle-in-cell (PIC) methods with Monte Carlo algorithms which simulate Coulomb collisions and charged/neutral interactions (charge exchange and electron impact ionization). The resulting transport code provides a fully kinetic description of transport and potential formation in a single spatial dimension (along the open field lines of the SOL) and two velocity components (parallel and perpendicular to those field lines). Plasma transport in the SOL system is modelled as a function of neutral particle recycling. The level of neutral recycling is varied by changing the average ionization frequency 〈νion〉 relative to the average Coulomb collision frequency 〈νc〉 over the range 0 ≤ ν′ ≤ 0.25, with ν′ ≡ 〈νion〉/〈νc〉. This study indicates that the plasma flow velocity, temperature and total kinetic energy flux decrease as the level of neutral particle recycling is increased. The variation of other transport quantities with neutral recycling intensity is presented, and the results are compared with those from other SOL transport models.

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Section: Ion Flow Energymentioning

confidence: 62%

“…6 of Ref. [25]), and then increases rapidly to its maximum value at the sheath boundary. A similar behaviour was observed in the v' = 0 .…”

Section: Ion Flow Energymentioning

confidence: 84%

“…5 of Ref. [25]). The flow velocity increases from zero at the midplane, exhibits a moderate dip near the location of the peak ionization rate (as shown in Fig.…”

Section: Ion Flow Energymentioning

confidence: 88%

Section: Ion Flow Energymentioning

confidence: 99%

Section: Ion Flow Energymentioning

confidence: 99%

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Particle simulations of collisional transport in a high recycling, diverted tokamak scrape-off layer

1990

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Divertor Plasma Analysis with Collisions

Dimoff

Parbhakar

1988

Contrib. Plasma Phys.

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The high recycling mode of divertor operation is found to depend on the spatial temperature gradient along the divertor length falling within limits set by the ratio of collision frequency with respect t o ionization rate. An analytlc expression for the neutral particle density necessary to sustain this mode is at least an order of magnitude greater at the divertor throat than previously assumed. PHYSICAL MODEL

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Properties of a Biased Divertor Scrape‐off Layer Plasma

Parbhakar

Lewandowski

1992

Contrib. Plasma Phys.

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The effect of biasing the divertor neutralization plates on the characteristic DroDerties of the scraoeroff layer (SOL) plasma is ikmtigated using a I-D fluih code along the magnetic fieid lines. The biasing effect is assumed to influence the e-folding density scale length ke which is then considered as a free parameter. The model includes radiative cooling in the divertor chamber, neutral reflux from the target plate and removal of neutral particles by ionization and pumping. Since pumping can only be done from the plenum region, we compute the escape probabilities to the plenum as a function of and then assume that a fixed fraction of the plenum neutrals is always pumped. We find that the average escape probability decreases with ke. The plasma density and velocity distribution near the plate are considerably modified, however the influence on the temperature is modest. The flux multiplication factor can increase by as much as 50% for the range of ke considered. An increase in neutral pressure is possible for negative biasing. I.ODUCTION E g the divertor neutralizing plates with respect to the chamber walls['' offers an interesting method to control dynamically the scrape-off la er (SOL) characteristics. Experimentally a change in the e-folding density scale length kc is observed['! which increases (decreases) for positively (negatively) biased plates as compared to the unbiased case. The change in Ac can strongly influence the recycling of neutral particles and hence the plasma density, temperature and the velocity distributions in the diverted SOL. Since impurity screening and the handling of plasma exhaust are strongly dependent on SOL parameters, it is important to estimate the effect of biasing on these parameters.Divertor modelling has seen rapid progress during the past decade[". Be inning with simple analyac models13', there has been evolution to two dimensional computer codes f45femploying realistic geometries. Most of these models use fluid equations, with given transport coefficients in combination with neutral particle transport models of varying sophistication. When the SOL is biased, non-ambipolar currents are generated and none of these codes are equipped to handle these currents. Some attempt in this direction was made in ref.[6], where the flow is considered to be non-ambipolar locally; however, global ambipolarity (is. the total current to the vessel walls is zero) was still maintained. The major difficulty in treating global non-ambipolarity lies in determining the two dimensional plasma potential distributions and the corresponding current densities for an arbitrary bias voltage. This problem has btcn cleverly dealt with in the case of toroidal limiter g~ometql'.~~, where the drift motions and electric currents were self consistently computed under biasing conditions. Lacking a detailed and accurate treatment of nonambipolar flow in a divertor SOL, it becomes imperative to study somewhat simpler but realistic problems where the effect of biasing can be included indirectly. We present...

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Parametric analyses of divertor plasmas

Cited by 6 publications

References 4 publications

Particle simulations of collisional transport in a high recycling, diverted tokamak scrape-off layer

Particle simulations of collisional transport in a high recycling, diverted tokamak scrape-off layer

Divertor Plasma Analysis with Collisions

Properties of a Biased Divertor Scrape‐off Layer Plasma

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