HIGH-FIELD MEASUREMENTS ON YBCO

We have performed resistance measurements on thin films of the high-te mperature superconductor YBa2Cu3O7 (YBCO) in applied magnetic fields t o above 200 T (2 MegaOersted) at temperatures as low as 2.5 K. The fie lds are produced by an explosively driven flux-compression system. We can see a particularly clear onset, without replotting the data, of th e ''hydrodynamic'' flow of vortices probably because of the very fast increasing field. The low temperature ''critical field'' for the field parallel to the c-axis of the sample is 135 T. Our data in the other direction are still preliminary. We discuss possible interpretation of our results.