Apparatus for vortex dynamics studies in high T-c samples using close cycle refrigerator and rf oscillators

The design, fabrication, and performance of an apparatus for measurements o f rf penetration depth in superconducting samples are described. The instru ment makes use of a close-cycle helium refrigerator and is capable of measu ring vortex dynamics in superconducting sample of volume as small as 1x10(- 3) cm(3) with a signal-to-noise ratio of 1400. The system has been tested f or a tunnel diode oscillator and an IC 74LS04 oscillator in the 3-5 MHz fre quency range. Both magnetic field magnitude and angular variations to the r esolution of 1 G and 0.05 degrees, respectively, are possible with the appa ratus. The system performance is evaluated by measuring the dynamical behav ior of vortices in platelet samples of Bi2Sr2CaCu2O8 and (Bi-Pb)(2)Sr2Ca2Cu 3O10 superconductors. (C) 1999 American Institute of Physics. [S0034-6748(9 9)04602-X].