Abstract
Cryogenic pellet injection will be the prime candidate to fuel future fusion power plants. In order to harvest optimum fueling performance, it is essential to inject pellets from the magnetic high field side of the tokamak. The pellet launching system of the tokamak ASDEX Upgrade injects cryogenic hydrogen pellets with a speed of up to 1000 m/s from the magnetic high field side via curved guiding tubes. Pellets passing the guiding tube are sliding on a gas cushion, generated by the Leidenfrost effect. The actual track has a rectangular cross section and is composed of a series of ellipses in order to generate the required 270° looping type turn; the path length is 17 m. The last part of this track is marked by strong geometrical constraints from the vacuum vessel port. The previous design was composed of a sequence of three sections of ellipses too, tangentially constant but discontinuous with regard to the curvature. It had been in operation for almost 20 years. Its steps in the curvature are supposed to limit the system performance. A novel and advanced geometry concept, adopting a method well-known from civil engineering (e.g., for the railroad track design), has been applied to develop an improved design. It relies on clothoid shape sections keeping the track curvatures continuous and, thus, provides a smooth transition between all the elements. The new design presented improves the pellet launching system performance on ASDEX Upgrade and provides knowledge for an advanced design of pellet guiding tubes in future fusion devices.
Highlights
The ASDEX Upgrade centrifuge pellet launching system has been in operation for more than 25 years.[1]
The previous design was composed of a sequence of three sections of ellipses too, tangentially constant but discontinuous with regard to the curvature
A novel and advanced geometry concept, adopting a method well-known from civil engineering, has been applied to develop an improved design
Summary
The ASDEX Upgrade centrifuge pellet launching system has been in operation for more than 25 years.[1] After some years of operation, the need to inject pellets from the magnetic high field side of the tokamak was identified.[2,3] the looping shaped guiding tube was established and has been in operation since (Fig. 1).[4] Many experiments for plasma fueling and for edge-localized mode (ELM). Thorough investigations have been performed in view of ITER6,7 in combination with the experience on ASDEX upgrade as a basis for the preparation of the EU-DEMO fueling system (Demonstration Fusion Power Reactor to follow ITER).[8]
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