Effect of scrape-off on tokamak radial transport

A kinetic code for simulation of collisionless magnetized plasma flow along expanding magnetic field lines to a neutralizer plate is developed and presented. A Monte Carlo description for the ion dynamics coupled with Boltzmann electrons is used to develop an iterative scheme for solution of the Vlasov equation and quasineutrality. The code has been used to simulate plasma flow in the edge region of stellarators with expanding magnetic field lines and neutral gas recycling at the neutralizer plate. The results show that the presence of a divergent magnetic field increases the pre-sheath potential drop above that obtained with a uniform field calculation. The increased potential drop generates an electrostatic barrier retarding the flow of high-Z impurity ions from the target plate towards the confined plasma. Neutral gas recycling increases the ion density and hence decreases the potential drop, amplifies the particle and energy fluxes to the wall, and reduces the average energy carried by each particle to the neutralizer plate.

Section: Effect Of Neutral Gas Recyclingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Simulation of plasma flow and potential formation in the non-uniform divertor magnetic field of a stellarator

Hussein¹,

Emmert²

1989

“…There are several theoretical papers devoted to the hydrogen ion transport in the scrape-off layer plasma under various physical conditions [3][4][5][6]. The results are, however, too complex to be useful for our calculations.…”

Section: Plasma Background and Impurity Sourcementioning

confidence: 99%

“…Thus, plasma transport and impurity sources at the walls become de-coupled from impurity transport. Although attempts have been made to solve the plasma transport problem in the scrape-off layer on the basis of the usual drift-kinetic equations [3][4][5][6] -there are papers, NUCLEAR FUSION, Vol.21, No. 5 (1981) which explicitly take account of high mass velocities in the drift-kinetic equations [7,8] -a self-consistent solution for the scrape-off layer plasma is still missing.…”

Section: Introductionmentioning

confidence: 99%

Impurity transport calculations for the limiter shadow region of a tokamak

Claaßen

Repp

1981

Impurity transport calculations are presented for the scrape-off layer of a tokamak with a poloidal ring limiter. The theory is based on the drift-kinetic equations for the impurity ions in their different ionization states. It is developed in the limit of low impurity concentrations under due consideration of electron impact ionization, Coulomb collisions with hydrogen ions streaming onto a neutralizing surface, a convection along the magnetic field, and a radial drift. The background plasma and the impurity sources at the walls enter the theory as input parameters. Numerical results are given for the radial profiles of density, temperature, particle flux, and energy flux of wall-released impurity ions as well as for the screening efficiency of the scrapeoff layer neglecting impurity re-emission from the limiter

“…Plasma flow in the divertor scrape-off zone has been treated theoretically from the neoclassical transport point of view by Hazeltine and Hinton [8], Daybelge [9], and El-Nadi [10]. The problem has also been treated by Boozer [11] using the Braginskii two-fluid equations, and by Mense 112] and Meade [13] using a more phenomenological approach, where loss terms representing the diverto.…”

Section: Introductionmentioning

confidence: 99%

Non-ambipolar transport in a magnetic divertor

Strawitch

Emmert

1981

Plasma transport is studied in a simulated magnetic divertor in the Wisconsin single-ring DC machine. The transport perpendicular and parallel to the magnetic field is shown to be non-ambipolar by a variety of measurements. The degree of the non-ambipolarity can be reduced by an appropriately designed divertor target plate, but not eliminated altogether. The density and temperature profiles in the scrape-off zone agree with the solutions of one-dimensional transport equations that assume classical cross-field diffusion due to ion-neutral collisions, classical cross-field conductivity due to electron-neutral collisions, and plasma flow parallel to the field at the local ion acoustic velocity.