An Analysis of the Nb3Sn Critical Current Data Obtained in Vamas Round Robins
Data sets obtained in VAMAS Round Robins of measurements on Nb3Sn conductors have been reduced to a form which can be handled analytically, by fitting them to the Kramer equation, expressed in the form: I.B = (A + K.B). The deviation of individual measurements from the equation, fitted to the set to which they belonged, was mostly around 0.5%, which was typically an order of magnitude better than the deviation between sets. A basic finding was that the standard deviation between sets increased with increasing magnetic field. During the Round Robin series, attempts were made to separate out possible sources of error by systematic control of experimental variables. Using the analysis at 11 Tesla: In the first series standard deviations of more than 16% were detected. In the last this was reduced to 3%, which still leaves an undesirable difference of nearly 10% between the highest and the lowest results. The differences are even larger at higher fields. The analysis has been used to indicate the level of accuracy required in current, magnetic field and voltage settings respectively and also the level of control required over the temperature and the strain to which the sample under test is subjected. Experimental factors related to possible errors are discussed and alternative procedures suggested, leading to proposals for future work.
KeywordsCritical Current Niobium Titanium Composite Superconductor Stainless Steel Holder Kramer Equation
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