Non quadratic RF losses in niobium sputter coated accelerating structures

Low field Q-values of more than 10/sup 10/ and maximum accelerating gradients E/sub a/ between 10 and 15 MV/m have been obtained in superconducting mono-cell and multi-cell accelerating cavities between 350 and 1500 MHz. The superconductor is niobium, which is magnetron-sputtered as a thin film (/spl sim/1-2 /spl mu/m) on a cavity made from copper sheet. The dependence of the slope of Q vs. E/sub a/ on temperature and frequency can be explained by RF magnetic flux trapped within intrinsic defects.<<ETX>>

[1]  W. Weingarten,et al.  Comparative measurements of niobium sheet and sputter coated cavities , 1987 .

[2]  J. Halbritter.  Surface Impedance and Granularity in Superconducting Cuprates , 1990 .

[3]  J. Clem.  Granular and superconducting-glass properties of the high-temperature superconductors , 1988 .

[4]  J. Halbritter.  On extrinsic effects in the surface impedance of cuprate superconductors by weak links , 1992 .

[5]  Daniel E. Oates,et al.  Measurements and modeling of linear and nonlinear effects in striplines , 1992 .

[6]  M. Tinkham,et al.  Physical Properties of the New Superconductors , 1989 .

[7]  J. Halbritter,et al.  rf Residual losses, surface impedance, and granularity in superconducting cuprates. , 1990 .

[8]  D. W. Cooke,et al.  Superconducting stripline model of intergranular flux penetration , 1992 .

[9]  Nathan Newman,et al.  High-temperature superconducting microwave devices: Fundamental issues in materials, physics, and engineering , 1993 .

[10]  C. Benvenuti,et al.  Superconducting 500 MHz accelerating copper cavities sputter-coated with niobium films , 1985 .

[11]  J. Halbritter,et al.  On oxygen enrichments in Nb surface layers and their apparent conductivity as observed by the superconducting penetration depth Δλ (T,f,Bac) , 1977 .

[12]  Vaglio,et al.  Residual surface resistance of polycrystalline superconductors. , 1991, Physical review. B, Condensed matter.

[13]  Oates,et al.  Nonlinear surface impedance for YBa2Cu3O7-x thin films: Measurements and a coupled-grain model. , 1993, Physical review. B, Condensed matter.

[14]  C. T. Roche,et al.  Power and magnetic field‐induced microwave absorption in Tl‐based high Tc superconducting films , 1991 .

[15]  M. Cardona,et al.  EVIDENCE FOR NORMAL REGIONS AT LOW TEMPERATURES IN THE SUPERCONDUCTING MIXED STATE , 1964 .

[16]  Cristoforo Benvenuti,et al.  Niobium films for superconducting accelerating cavities , 1984 .

[17]  J. Halbritter.  On intrinsic and extrinsic effects in the surface impedance of cuprate superconductors , 1992 .

[18]  H. Safa,et al.  Power dissipation at high fields in granular RF superconductivity , 1991 .

[19]  A. M. Portis,et al.  Microwave power-induced flux penetration and loss in high-temperature superconductors , 1992 .

[20]  Alan M. Portis,et al.  Electrodynamics Of High Temperature Superconductors , 1993 .

[21]  P. Kneisel,et al.  Investigations of Additional Losses in Superconducting Niobium Cavities Due to Frozen-In Flux , 1973 .