Studies of tritiated co-deposited layers in TFTR Page: 4 of 18
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plasma conditions before tritium injection and the isotopic ratio of T/D fueling was 3%. In TFTR
the average tritium retention fraction was 51% during normal plasma operations and 16% over the
long term including clean up periods[6,7]. Tritium was removed from the vessel by air ventilation
and glow discharge cleaning during two maintenance periods and after the termination of plasma
The analysis of plasma facing components from tokamaks that have been operated with tritium
plasmas is uniquely valuable in understanding the behavior of tritium in these devices. TFTR
operated with toroidal plasmas with a circular cross-section that were in contact with an inner
toroidal 'bumper' limiter. The total area of the bumper limiter was 22 m2 and it is divided into 20
bays (labeled A-T) each composed of 24 rows of tiles, 4 tiles wide. Each bay is curved in both
toroidal and poloidal directions and the midplane center extends out 4.6 mm from a true toroidal
surface. The midplane tiles are 125 mm wide and 81 mm high. High heat flux areas are covered
with Fiber Materials Inc. 4D coarse weave carbon fiber composite (CFC) tiles and Hercules 3-D
fine weave CFC tiles and the remainder Union Carbide AXF-5Q isotropic graphite. The outer
vacuum vessel is 304 stainless steel and is protected by several groups of graphite tiles arranged
poloidally. Tiles also protect high heat flux locations on the edge of RF antennas and outboard
surfaces in the line of sight of the neutral heating beams.
The plasma facing surfaces portray a rich and spatially complex imprint of many years of TFTR
plasma operations (Fig.1). The connection length of a field line launched from the limiter surface
varies strongly with spatial position and controls the balance between erosion and co-
deposition. In Fig. 1, co-deposition is visible in a diagonal band from the upper right to lower
left of bay K and on the left side of the poloidal limiter tile at the floor. Co-deposited layers on
graphite tiles began to flake after the termination of plasma operations[ 12,13]. Minor flaking can
now be observed on CFC tiles and of co-deposited layers on the stainless steel vessel floor. The
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Skinner, C.H.; Gentile, C.A.; Ascione, G.; Carpe, A.; Causey, R.A.; Hayashi, T. et al. Studies of tritiated co-deposited layers in TFTR, report, June 28, 2000; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc709360/m1/4/: accessed October 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.