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The stellarator Wendelstein W7-X, a fusion plasma experiment, is almost ready to be set into plasma operation. Seventy superconducting coils produce the magnetic field that is required to confine the plasma. The coils are arranged in a cryostat vacuum vessel in shape of a torus. The superconductors are cooled by supercritical helium down to the nominal operating temperature between 3 K and 4 K. Before operation, vacuum leak search was performed on the machine, both the cryostat and the plasma vessel. Most of the leaks could be fixed; however not all. But the residual helium leak rate is too small to hamper the successful coil operation. A refined leak search is pending for the future, in order to localize and fix all the remaining leaks. This paper describes a numerical regression analysis, performed to localize these remaining leaks. The regression analysis could gain information on the size and position of the leak, and, at least in principle, on the hydraulic helium flow behavior inside the leak channel. It could be a helpful complement to the standard leak search techniques that had been used before. [ABSTRACT FROM AUTHOR]

A new plasma fusion experiment, the Wendelstein 7-X (W7-X) has been built in the Max-Planck Institute for Plasma Physics in Greifswald, Germany. A cryostat vacuum tank, shaped like a torus, hosts 70 superconducting magnetic coils to produce a toroidal magnetic field that will confine a fusion relevant plasma. The cryostat tank has a volume of about 420 m 3 and is equipped with several hundreds of vacuum ports, feed-throughs and service openings. Nested inside the cryostat is the plasma vessel with a volume of about 80 m 3 , also shaped like a torus. This plasma vessel is connected to the outside by 254 ports that traverse the cryostat. These ports are needed as access for plasma diagnostics, plasma heating and the supply of cooling media. We report in this paper on the vacuum leak search on the W7-X cryostat, both for the internal piping as well as the integral leak search of the entire vessel against air. This is the initial leak search prior to the first cool-down of W7-X. Emphasis is put on the description of the methods, rather than on the results. The technical commissioning of the cryostat vacuum system within a limited time was the primary task; the emphasis was therefore much more on achieving practical results (the leak-tightness) rather than answering fundamental questions. [ABSTRACT FROM AUTHOR]

Abstract: For the stellarator Wendelstein 7-X, a plasma fusion experiment, the performance of the superconducting coils is tested in a cryogenic test facility. Focus is on the quench behaviour of these coils. Some key data of the coils are given here. The coil quench data, obtained during the tests, are compared to GANDALF code calculations. GANDALF is a one-dimensional finite elements code for the simulation of the quench properties of superconducting CICC cables. Good consistency between measurement and calculation is found for the development of the resistive voltage and temperature increase during the quench. [Copyright &y& Elsevier]