INVESTIGATION OF TRANSPORT PROCESSES CLOSE TO LIMITER SURFACES IN TEXTOR-94

WESCHENFELDER F WINTER J KOGLER U ESSER HG PHILIPPS V POSPIESZCZYK A SCHWEER B VONSEGGERN J TOKAR MZ WIENHOLD P

F. Weschenfelder et al., INVESTIGATION OF TRANSPORT PROCESSES CLOSE TO LIMITER SURFACES IN TEXTOR-94, Plasma physics and controlled fusion, 38(12A), 1996, pp. 311-323

13

INGLESE

Article

Phsycs, Fluid & Plasmas

Plasma physics and controlled fusion → ACNP

0741-3335

38

12A

1996

311 - 323

ISI

0741-3335(1996)38:12A<311:IOTPCT>2.0.ZU;2-T

Silane gas (SiD4) has been injected through a hole in the surface of t est limiters during ohmically heated tokamak discharges in TEXTOR-94. The gas injection led to the deposition of a thin layer around the inj ection hole which was close to the area of the highest heat load. The layer was eroded in discharges without silane injection and spectrosco pic measurements prove that the erosion of limiter material is reduced in areas where the layer is deposited. Surface analyses reveal that t he layer was formed not only by the injected silicon but also by a lar ge amount of carbon which must originate from other plasma-facing comp onents. The preferential direction (symmetry line) of the deposition p attern is tilted by congruent to 25 degrees relative to the magnetic f ield lines. Calculations with the Monte Carlo code ERO-TEXTOR were use d to interpret the data. The shape of the Si-deposition pattern can be recovered quantitatively by including an E x B drift in a radial elec tric field originating from the gradient in the electron temperature p rofile above the limiter surface. The deposition pattern allows the 'i maging' of the complex plasma Bow close to the surface. To obtain agre ement between calculated and experimentally observed deposition effici encies a sticking coefficient much smaller than I and the influence of an electric field parallel to B have to be considered.