Physical Review Special Topics-Accelerators and Beams
In the last few years superconducting radio-frequency (rf) cavities made of high-purity ( residual resistivity ratio > 200) niobium achieved accelerating gradients close to the theoretical limits. An obstacle towards achieving reproducibly higher fields is represented by "anomalous'' losses causing a sharp degradation of the cavity quality factor when the peak surface magnetic field (Bp) is above about 90 mT, in the absence of field emission. This effect, called "Q drop'' has been measured in many laboratories with single- and multicell cavities mainly in the gigahertz range. In addition, a low-temperature (100 - 140 °C) "in situ'' baking of the cavity was found to be beneficial in reducing the Q drop. In order to gain some understanding of the nature of these losses, a single- cell cavity has been tested in the TM010 and TE011 modes at 2 K. The feature of the TE011 mode is to have zero electric field on the cavity surface, so that electric field effects can be excluded as a source for the Q drop. This article will present some of the experimental results for different cavity treatments and will compare them with existing models.
Original Publication Citation
Ciovati, G., & Kneisel, P. (2006). Measurement of the high-field q drop in the tm010 and te011 modes in a niobium cavity. Physical Review Special Topics-Accelerators and Beams, 9(4), 042001. doi: 10.1103/PhysRevSTAB.9.042001
Ciovati, Gianluigi and Kneisel, Peter, "Measurement of the High-Field Q Drop in the TM010 and TE011 Modes in a Niobium Cavity" (2006). Physics Faculty Publications. 44.