Modeling of localized impulsive injection of neutrals and plasma response

Tokar, M. Z.

doi:10.1088/1361-6587/aa6219

Cited by 4 publications

(5 citation statements)

References 25 publications

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“…However, for T e_pl above 3-4 eV the W sputtering yield by Ne together with that by Be and by W self-sputtering provide a simulated W flux, which is comparable to that experimentally observed for the most common JET ELMy H-mode situations, once the data are averaged over times τ A >>1/f ELM [6]. Indeed, in JET ELMy-H mode the experimental Γ W is found to be in the range 3-9x10 19 /s [20,21], as in COREDIV simulations. In particular, for this series of pulses the intensity of the WI emission line at 401 nm, measured at the outer divertor, shows a slight increase with increasing Γ Ne , in qualitative agreement with the calculated COREDIV total W fluxes, which increase, in total, from about 6 to 9.5 x 10 19 /s, Fig.5.…”

Section: Discussionsupporting

confidence: 67%

“…The reduction of T e (X-point) leads to a shift in the ionization and recombination front [18], with possible related change of the neutral compression in the divertor. Another possibility is related to the fact that while in COREDIV the sedeed neon enters directly the plasma, in the experiment neon is puffed in the private region: increasing the divertor density with increasing Γ Ne (exp), the Ne penetration depth may decrease, resulting in the reduction of the effective Ne seeding rate [19].…”

Section: Discussionmentioning

confidence: 99%

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Simulation of JET ITER-Like Wall pulses at high neon seeding rate

et al. 2017

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A series of neon seeded JET ELMy H-mode pulses is considered from the modeling as well as from the experimental point of view. For two different Ne seeding rates and two different D puffing gas levels the heating power, P heat , is in the range 22-29.5 MW. The main focus is on the numerical reconstruction of the total radiated power (which mostly depends on the W concentration) and its distribution between core and divertor and of Z eff (which mostly depends on the Ne concentration). To model with the self-consistent code COREDIV the core and the SOL two input parameters had to be adjusted case by case: the SOL diffusivity, D SOL , and the core impurity inward pinch, v pinch . D SOL had to be increased with increasing Γ Ne and the level of v pinch had to be increased with decreasing the ELM frequency, f ELM . Since for any given gas puffing level f ELM decreases with the Ne seeding rate, this might lead to a limitation in the viability of reducing the target heat load by Ne seeding at moderate Γ D , while keeping acceptably low Z eff . In the considered range of temperatures and densities of the SOL, the numerical results suggest the balance between friction and thermal forces to be in favor of the frictional drag for tungsten, thus providing a W screening effect.

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Section: Discussionsupporting

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Simulation of JET ITER-Like Wall pulses at high neon seeding rate

et al. 2017

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“…Here we do not describe the whole spectrum of the x and ρ velocity components but characterize their values by the averaged ones V x = V bs,m and V ρ = ±V bs,m , by taking into account particles moving both outwards, the sign +, and towards, the sign −, the opening axis. A comparison of calculations done under this approximation [10] and by using a broad distribution of velocity components [11] shows that they provide close enough results. The present simplified approach diminishes, however, the calculation time significantly.…”

Section: Recycling Molecules and Atomsmentioning

confidence: 64%

“…The question to what extent the local plasma parameters may be changed by the outflow of the gas from the duct has to be investigated in the future, e.g. on the basis of the model in [10]. This research demonstrated that the ionization of the gas, penetrating into the SOL, may lead to dramatic growth of the local density and cooling of the plasma to a temperature of 1 eV.…”

Section: Resultsmentioning

confidence: 99%

Assessment for erosion of and impurity deposition on first mirrors in a fusion reactor

Tokar

2018

Nucl. Fusion

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Hot atoms with chaotically directed velocities are generated by charge-exchange with plasma ions of neutrals recycling from the vessel wall of a fusion reactor. Some of them flee into openings in the vessel made for ducts guiding to diagnostic installations; in particular, to first mirrors for optical observations. On the one hand, hot atoms, hitting the mirror directly, can erode its surface. On the other hand, impurity species, released from the walls of the vessel and of the diagnostic duct, migrate to the mirror and can be deposited there. Both the erosion of and impurity deposition on the mirror decline its reflection properties. Models elaborated to describe processes above are outlined, including a 2D kinetic description for neutral species in the vicinity of the duct opening, an assessment for the erosion of the duct walls and mirror surface by hot atoms, estimates for influxes of the wall material into the duct and a consideration of the migration of impurity atoms along the duct. Calculations are done for the conditions predicted for a fusion reactor like DEMO. The rates for erosion of and impurity deposition on first mirrors of Mo are assessed versus input parameters such as the duct radius, the distance from the opening to the mirror, the density ng of the working gas in the duct, the probabilities for impurity sticking to the duct wall and mirror surface. It is demonstrated that, by ng exceeding a level of m−3, the mirror sputtering can be reduced to the target level of 1 nm per full power year. Moreover, for long enough ducts the erosion rate of impurities deposited onto the mirror exceeds their deposition one and no formation of impurity precipitations on the mirror surface has to be expected.

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“…One can see that the enhancement of n g above a level of 2 Á 10 19 m À3 should lead to the reduction of h sp below the target level of 1nm=pfy. The question, to what extent the local plasma parameters may be changed by the outflow of the gas from the duct, has to be investigated in the future on the basis of approaches developed in [16]. There, it has been demonstrated that the ionization of the gas outflowing into the SOL can lead to dramatic growth of the local density and cooling of the plasma to a temperature of 1 eV.…”

Section: Results Of Calculationsmentioning

confidence: 99%

Noise-Free Rapid Approach to Solve Kinetic Equations for Hot Atoms in Fusion Plasmas

Tokar¹

2019

Plasma Science and Technology - Basic Fundamentals and Modern Applications

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At the first wall of a fusion reactor, charged plasma particles are recombined into neutral molecules and atoms recycling back into the plasma volume where charge exchange (cx) with ions. As a result hot atoms with chaotically directed velocities are generated which can strike and erode the wall. An approach to solve the kinetic equation in integral form for cx atoms, being alternative to statistical Monte Carlo methods, has been speeded up by a factor of 50, by applying an approximate pass method to evaluate integrals, involving the ion velocity distribution function. It is applied to two-dimensional transfer of cx atoms near the entrance of a duct, guiding to the first mirror for optical observations. The energy spectrum of hot cx atoms, escaping into the duct, is calculated and the mirror erosion rate is assessed. Computations are done for a molybdenum first mirror under plasma conditions expected in the fusion reactor DEMO. Kinetic modeling results are compared with those found with a diffusion approximation valid in very cold and dense plasmas. For ducts at the torus outboard a more rigorous kinetic consideration predicts an erosion rate by a factor up to 2 larger than the diffusion approximation.

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Modeling of localized impulsive injection of neutrals and plasma response

Cited by 4 publications

References 25 publications

Simulation of JET ITER-Like Wall pulses at high neon seeding rate

Simulation of JET ITER-Like Wall pulses at high neon seeding rate

Assessment for erosion of and impurity deposition on first mirrors in a fusion reactor

Noise-Free Rapid Approach to Solve Kinetic Equations for Hot Atoms in Fusion Plasmas

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