Q-disease Investigations

In 1989 R. Roeth [1] observed at the University of Wuppertal a significant degradation of the Q-value of a 1500 MHz cavity made from high purity niobium after it had been kept at nitrogen temperature for several days after the initial test in superfluid helium. A temperature map indicated that these unexpected losses were distributed uniformly over the whole cavity surface. The initial hypothesis expressed in [1] of precipitation of the Nb-hydride phase was supported by a variety of subsequent experiments in various laboratories around the world.

Jlab contributed to the understanding and elimination of this phenomenon by e.g. investigating the dangerous temperature region, in which the losses occur, and by quantifying the length of time in this temperature region for the losses to take place [2]

[1] R.Roeth et al.; Proc. 2 nd European Part. Acc. Conf., Nice, France,Vol.2, p. 1097 (1990)