Upgrade of the 15 T JUMBO Facility for Time Dependent High Resolution $U(I)$ -Measurements

The detailed knowledge of the voltage-current characteristics U(I) of a superconductor and therefore its critical current I _C and n-value is a prerequisite for the application of these materials. In the past, we focussed on the high resolution U(I)-determination under quasi steady-state conditions in order to avoid transient voltage contributions and to average out noise in U(I) . The drawback of this measuring technique is that possible additional effects occurring during the variation of the current such as flux flow instabilities are, in principle, not detected. Therefore, the facility JUMBO was upgraded to allow also continuous high resolution measurements of U(I) while ramping the current. In addition to the advancement of the measuring equipment, grounding and shielding of the whole facility was improved to reduce the influence of electromagnetic perturbations. In this paper, first measurement results with this new setup are presented and the impact of the current-ramping on the U(I)-measurements is discussed.