Long-term erosion and deposition studies of the main graphite limiter in TEXTOR

Abstract

Erosion and deposition behaviour of the TEXTOR main toroidal belt limiter ALT-II has been studied for two generations of limiter tiles with different surface shapes. Two specially prepared tiles with marker holes were subsequently exposed during experimental campaigns with a total plasma duration of > 7000 s and a surface averaged background ion fluence exceeding 2⋅10 25 m -2 . The tile surface relief was measured by optical profilometry and SIMS before and after the exposure. The highest surface erosion of > 10 μm on both tiles was observed in regions with an angle of incidence of the magnetic field α of > ~ 1°, whereas in the regions with α ~ 0.1° both net-erosion and net-deposition were observed depending on the tile shaping. The marker holes were always deposition dominated. Modelling by the ERO code explains qualitatively the surface erosion and deposition behaviour in terms of background flux dilution for shallow angles of incidence.

Long-term carbon transport and fuel retention in gaps of the main toroidal limiter in TEXTOR

“…The carbon deposition rates at the gap entrance of up to 3 nm/s are similar to the maximum values found on the top surface of the ALT-II limiter [14][15][16]. However, the rates decay with a characteristic length of about 0.7 mm towards the bottom.…”

“…The deeper penetration of the magnetic field lines in the toroidal than in poloidal gaps is probably the main reason for this effect. The rooflike geometry of the ALT-II limiter leads to the step-wise transport of carbon towards the limiter tip, the position of the toroidal gap [14][15][16]. This can intensify to the deposition in the toroidal gap.…”

“…Toroidally the tiles are shaped according to the toroidal curvature of the LCFS. The tile shaping leads to the net-deposition of carbon in the central poloidal part of the limiter (about one third of the limiter area), where the angle of incidence of the magnetic field is shallower [14][15][16]. To the edges, the limiter surface is typically erosion dominated.…”

Multi machine scaling of fuel retention in 4 carbon dominated tokamaks

“…The particle flux on the limiter is estimated to be in the range 3×10 21 D/s 10 22 D/s [12]. The upper value of 10 22 D/s is taken here.…”

Dimple optimization for XPS characterization of TEXTOR tile depositions

“…These concerns have been highlighted by the detailed studies of plasma facing components (PFC) after each operational campaign of the JET tokamak [1][2][3][4][5][6][7][8]. In the same way, erosion/deposition studies have been carried out in the TEXTOR tokamak (FZJ, Germany) [9].…”