SRF2017 - List of Keywords (feedback)

Paper	Title	Other Keywords	Page
TUYBA02	Thermal Boundary Resistance Model and Defect Statistical Distribution in Nb/Cu Cavities	ion, cavity, interface, ISOL	374
	R. Vaglio UniNa, Napoli, Italy V. Palmieri INFN/LNL, Legnaro (PD), Italy
	The ‘Q-slope' problem strongly limits the application of niobium thin film sputtered cavities in high field accelerators. Here we consider the hypothesis that the Q-slope is related to local enhanced of the thermal boundary resistance at the Nb/Cu interface, due to poor thermal contact between film and substrate. We introduce a simple model that directly connects the Q versus Eacc curves to the distribution function f(RNb/Cu) of RNb/Cu thermal contact at the Nb/Cu interface over the cavity surface. Starting from the experimental curves, using inverse problem methods, we deduce the distribution functions generating those curves. The technique has been applied to cavities by different groups, including LNL/INFN and ISOLDE/CERN. In all cases to explain the data it is sufficient to assume that only a small fraction of the film over the cavity surface is in poor thermal contact with the substrate. The distribution functions typically follow a simple power-law statistical distribution and are temperature independent. The full analysis supports the hypothesis that the main origin of the Q-slope in thin film cavities is indeed related to bad adhesion at the Nb/Cu interface.
	Slides TUYBA02 [0.988 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYBA02
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPB079	Simulations of RF Field-induced Thermal Feedback in Niobium and Nb3Sn Cavities	ion, cavity, niobium, simulation	920
	J. Ding, D.L. Hall Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Liepe Cornell University, Ithaca, New York, USA
	Thermal feedback is a known limitation for SRF cavities made of low-purity niobium, as the increased losses at higher temperature described by BCS theory create a feedback mechanism that can eventually result in a runaway effect and associated cavity quench. In a similar manner, niobium cavities coated with Nb3Sn may also be subject to increased losses from thermal feedback, as Nb3Sn is possessed of a much lower thermal conductivity than niobium, although this effect will be mitigated by the thin film nature of the coating. In order to better understand the degree to which thermal feedback plays a role in the performance of Nb3Sn cavities, it is necessary to understand how the various components of the problem play a role in the outcome. In this paper, we present the first results from simulations performed at Cornell University that model RF induced thermal feedback in both conventional niobium cavities and niobium cavities coated with a thin film of Nb3Sn. The impacts of layer thickness, niobium substrate thermal conductivity, and trapped flux on the performance of the cavity are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB079
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FRXBA02	High Precision RF Control for SRF Cavities in LCLS-II	ion, cavity, controls, LLRF	944
	L.R. Doolittle, K.S. Campbell, Q. Du, G. Huang, J.A. Jones, C. Serrano, V.K. Vytla LBNL, Berkeley, California, USA S. Babel, A.L. Benwell, M. Boyes, G.W. Brown, D. Cha, J.H. De Long, J.A. Diaz Cruz, D.B. Greg, B. Hong, R.S. Kelly, A. McCollough, A. Ratti, C.H. Rivetta SLAC, Menlo Park, California, USA R. Bachimanchi, C. Hovater, D.J. Seidman JLab, Newport News, Virginia, USA B.E. Chase, E. Cullerton, J. Einstein, D.W. Klepec Fermilab, Batavia, Illinois, USA
	Funding: This work supported under DOE Contract DE-AC02-76SF00515 The unique properties of SRF cavities enable a new generation of X-ray light sources in XFEL and LCLS-II. The LCLS-II design calls for 280 L-band cavities to be operated in CW mode with a Q_L of 4x10⁷, using Single-Source Single-Cavity control. The target RF field stability is 0.01% and 0.01 degree for the band above 1 Hz. Hardware and software implementing a digital LLRF system has been constructed by a four-lab collaboration to minimize known contributors to cavity RF field fluctuation. Efforts include careful attachment to the phase reference line, and minimizing the effects of RF crosstalk by placing forward and reverse signals in chassis separate from the cavity measurement. A low-noise receiver/digitizer section will allow feedback to operate with high proportional gain without excessive noise being sent to the drive amplifier. Test results will show behavior on prototype cryomodules at FNAL and JLab, ahead of the 2018 final accelerator installation.
	Slides FRXBA02 [3.425 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-FRXBA02
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Other Keywords

Page

TUYBA02

Thermal Boundary Resistance Model and Defect Statistical Distribution in Nb/Cu Cavities

ion, cavity, interface, ISOL

374

R. Vaglio
UniNa, Napoli, Italy
V. Palmieri
INFN/LNL, Legnaro (PD), Italy

The ‘Q-slope' problem strongly limits the application of niobium thin film sputtered cavities in high field accelerators. Here we consider the hypothesis that the Q-slope is related to local enhanced of the thermal boundary resistance at the Nb/Cu interface, due to poor thermal contact between film and substrate. We introduce a simple model that directly connects the Q versus Eacc curves to the distribution function f(RNb/Cu) of RNb/Cu thermal contact at the Nb/Cu interface over the cavity surface. Starting from the experimental curves, using inverse problem methods, we deduce the distribution functions generating those curves. The technique has been applied to cavities by different groups, including LNL/INFN and ISOLDE/CERN. In all cases to explain the data it is sufficient to assume that only a small fraction of the film over the cavity surface is in poor thermal contact with the substrate. The distribution functions typically follow a simple power-law statistical distribution and are temperature independent. The full analysis supports the hypothesis that the main origin of the Q-slope in thin film cavities is indeed related to bad adhesion at the Nb/Cu interface.

Slides TUYBA02 [0.988 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYBA02

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPB079

Simulations of RF Field-induced Thermal Feedback in Niobium and Nb3Sn Cavities

ion, cavity, niobium, simulation

920

J. Ding, D.L. Hall
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Liepe
Cornell University, Ithaca, New York, USA

Thermal feedback is a known limitation for SRF cavities made of low-purity niobium, as the increased losses at higher temperature described by BCS theory create a feedback mechanism that can eventually result in a runaway effect and associated cavity quench. In a similar manner, niobium cavities coated with Nb3Sn may also be subject to increased losses from thermal feedback, as Nb3Sn is possessed of a much lower thermal conductivity than niobium, although this effect will be mitigated by the thin film nature of the coating. In order to better understand the degree to which thermal feedback plays a role in the performance of Nb3Sn cavities, it is necessary to understand how the various components of the problem play a role in the outcome. In this paper, we present the first results from simulations performed at Cornell University that model RF induced thermal feedback in both conventional niobium cavities and niobium cavities coated with a thin film of Nb3Sn. The impacts of layer thickness, niobium substrate thermal conductivity, and trapped flux on the performance of the cavity are discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB079

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FRXBA02

High Precision RF Control for SRF Cavities in LCLS-II

ion, cavity, controls, LLRF

944

L.R. Doolittle, K.S. Campbell, Q. Du, G. Huang, J.A. Jones, C. Serrano, V.K. Vytla
LBNL, Berkeley, California, USA
S. Babel, A.L. Benwell, M. Boyes, G.W. Brown, D. Cha, J.H. De Long, J.A. Diaz Cruz, D.B. Greg, B. Hong, R.S. Kelly, A. McCollough, A. Ratti, C.H. Rivetta
SLAC, Menlo Park, California, USA
R. Bachimanchi, C. Hovater, D.J. Seidman
JLab, Newport News, Virginia, USA
B.E. Chase, E. Cullerton, J. Einstein, D.W. Klepec
Fermilab, Batavia, Illinois, USA

Funding: This work supported under DOE Contract DE-AC02-76SF00515
The unique properties of SRF cavities enable a new generation of X-ray light sources in XFEL and LCLS-II. The LCLS-II design calls for 280 L-band cavities to be operated in CW mode with a Q_L of 4x10⁷, using Single-Source Single-Cavity control. The target RF field stability is 0.01% and 0.01 degree for the band above 1 Hz. Hardware and software implementing a digital LLRF system has been constructed by a four-lab collaboration to minimize known contributors to cavity RF field fluctuation. Efforts include careful attachment to the phase reference line, and minimizing the effects of RF crosstalk by placing forward and reverse signals in chassis separate from the cavity measurement. A low-noise receiver/digitizer section will allow feedback to operate with high proportional gain without excessive noise being sent to the drive amplifier. Test results will show behavior on prototype cryomodules at FNAL and JLab, ahead of the 2018 final accelerator installation.

Slides FRXBA02 [3.425 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-FRXBA02

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)